Weather

DESCRIBE the conditions associated with occluded fronts

properties of warm/cold, combination of cloud types, combination of turbulence, purple Occluded fronts form when a faster moving cold front overtakes a slower moving warm front. There are two types of occluded fronts, cold and warm. The type of occlusion that forms depends on which front remains in contact with the ground. For example, if the cold front remains in contact with the ground, then it is named a cold front occlusion. The wind shift across either type of occlusion will be a 180° shift, as there are actually two fronts in the same location. Therefore, ahead of the occlusion, the winds will be the same as those ahead of the warm front, and behind the occlusion, the wind will be from the same direction as behind the cold front: the wind shift is SE to NW. Because the occluded front is the result of the meeting of both a cold front and a warm front, the weather associated with the occlusion will be a combination of both types of frontal weather.

DESCRIBE the flight conditions associated with the troposphere

> As Altitude increases, air density decreases > Within the troposphere, the temperature normally decreases with increasing altitude. Large amounts of moisture and condensation nuclei are found in the troposphere because of its closeness to the Earth's surface, and nearly all weather occurs here. Winds are generally light near the Earth's surface and increase with altitude. Wind speeds over 200 knots may occur near the top of the troposphere.

DESCRIBE the flight conditions associated with the tropopause

> Temperature in this layer is constant with altitude. > The strongest winds, those of the jet stream, occur just below the tropopause. Moderate to severe turbulence is sometimes associated with the wind shear caused by the jet stream.

DEFINE the term front

A front is an area of discontinuity that forms between two contrasting air masses when they are adjacent to each other. A front can be thought of as a border, boundary, or line between the air masses. These air masses must have sufficiently different temperature and moisture properties- the defining characteristics of an air mass-otherwise there would be little reason to distinguish between them. Since air masses cover many thousands of square miles, the boundary between them can be hundreds of miles long. As air masses are three-dimensional, fronts are, as well. The point where a front comes in contact with the ground is called the surface front. The surface front is the line that is plotted on surface analysis charts with different colors and shapes representing each type of front, as pictured in Table 3-1.

DEFINE dew point depression

Degree difference between air temperature and TD If there is a difference between the air temperature and the dew point temperature, this is known as the dew point depression, or dew point spread, and the dew point will always be the lower of the two. The dew point can never be higher than the air temperature: only equal to or less than. This spread provides a good indication of how close the atmosphere is to the point of saturation. When the dew point depression reaches about 4° F, the air is holding close to the maximum amount of water vapor possible. If this spread continues to decrease, moisture will begin to condense from the vapor state to the liquid (or solid) state, and become visible. This visible moisture can form dew or frost on exposed surfaces, fog near the ground, or clouds higher in the atmosphere.

DESCRIBE how temperature inversions are examples of wind shear turbulence

Differences in how winds behave at low altitude Extreme wind shear turbulence may be formed when strong inversion exists near ground. Stable conditions near ground If strong winds exist in upper warmer air Wind shear produced at layer boundary Sudden change in wind direction/velocity causes loss of airspeed, lift. Can be catastrophic if not compensated. Closer inversion to ground, less time to react. Can be unexpected in clear air. Compensate with added airspeed. Anticipate higher descent rates.

DESCRIBE the types of precipitation

Drizzle - liquid and freezing Rain - liquid and freezing Frozen - hail, ice pellets, snow and snow grains

STATE the temperature range most conducive to structural icing

0° to -20°C

DESCRIBE the characteristics of a squall line

A squall line is a line of violent thunderstorms. They are indicated on surface charts by a dashed, double-dotted red line. They develop 50 to 300 miles ahead of the cold front and roughly parallel to it. They form when cold air downdrafts flowing ahead of a cold front lift additional warm, unstable air. The uplifted air develops its own updrafts and downdrafts and starts the thunderstorm development cycle (Figure 3-11). Sometimes, however, squall lines can be located nowhere near a cold front, possibly from the convergence of air flows at one location. Squall lines are usually the most intense during the late afternoon and early evening hours, just after maximum daytime heating. It is often impossible to fly through squall lines, even with radar, since the storms are extremely close to one another. Similar to cold fronts, Squall lines will also have a 90° wind shift from the SW to the NW.

DESCRIBE the use of In-Flight Weather Advisories

AIRMETs and SIGMETs are available on the ADDS website and provide information on potentially hazardous weather phenomena. The reports may be displayed in either graphic or textual formats. SIGMETs (WS) advise of SIGnificant METeorological information other than convective activity that is potentially hazardous to all aircraft. WSs are issued for the conterminous US by NAWAU and are valid for up to 4 hours when any of the following weather phenomena occur or are forecast over an area of at least 3000 square miles: Severe or extreme non-convective turbulence, or CAT not associated with thunderstorms Severe icing not associated with thunderstorms Widespread dust storms or sandstorms lowering surface and/or flight visibilities to less than 3 miles Volcanic eruption and ash clouds Convective Sigmet- Appended to each WST is an outlook valid for up to 4 hours beyond the end of the WST. They are not scheduled, but rather issued as needed, when any of the following occurs and/or is forecast to occur for more than 30 minutes of the valid period regardless of the size of the area affected: Tornadoes Lines of thunderstorms (squall line 60miles long over 40% of it) Embedded thunderstorms Thunderstorm areas greater than or equal to thunderstorm intensity (VIP level) of four or greater with an area of coverage of 40% or more Hail greater than or equal to 3/4 inch in diameter or greater and/or wind gusts to 50 knots or greater AIRMETs (WA) also advise of significant weather phenomena other than convective activity but indicate conditions at intensities lower than those that trigger SIGMETs. Both are intended for dissemination to all pilots in the enroute phase of flight to enhance safety, and are available for preflight planning, as well. - still indicate intense weather but not high enough for other types

IDENTIFY the hazards of aircraft icing

Aerodynamic Effects Most hazardous aspect of structural icing. Alters shape of airfoil changing the stall angle of attack. Performance Effects Decreases Lift Thrust Range Increases Drag Weight Fuel consumption Stall speed Effects on stall speed can be fatal if not predicted. All others provide time to take appropriate action (except lift, during takeoff). Other Effects Pitot-static system - faulty instrument indications Inhibits control surface movement and antenna transmission.

DEFINE the term air mass

An air mass is a large body of air that has essentially uniform temperature and moisture conditions in a horizontal plane, meaning that there are no abrupt temperature or dew point changes within the air mass at a given altitude. It may vary in size from several hundred to more than several thousand square miles (Figure 3-1).

DESCRIBE the use of METARs in flight planning

Aviation Routine Weather Reports (METARs) Provide rapid and efficient means of transmitting latest observed weather to meteorologists and aircrews Can determine weather at a primary or alternate destination Can determine whether an airfield is under IFR or VFR operation Can help determine trends in weather, to see if weather is developing as forecast

DESCRIBE the use of Severe Weather Watch messages

Aviation Severe Weather Watch Bulletins are issued for two types of expected severe weather conditions: Funnel clouds or tornadoes Severe thunderstorms, defined by frequent lightning and one or more of the following: 50 knots of wind or greater 3/4 inch diameter hail or larger

LIST the types of icing used in Pilot Reports (PIREPs)

Clear Icing Found at temperatures between 0° and -10° C. Large water droplets freeze slowly, spreading out and assuming shape of airfoil. Found in cumulus clouds; unstable conditions. Rime Icing Found at temperatures between -10° and -20° C. Small water droplets freeze instantaneously, retaining shape. Air bubbles do not escape, causing opaque (milky white) color and brittleness. Found in stratiform clouds; stable conditions. Mixed Icing Combination of clear and rime. Most common type. Found at temperatures between -8° and -15° C. Lumpy (like rime) but hard and dense (like clear).

DESCRIBE the conditions associated with an inactive front

Clouds and precipitation do not accompany inactive fronts. Sometimes the warm air mass is too dry for clouds to form even after the air is lifted and cooled. Inactive fronts may also be referred to as dry fronts. The reason for showing an inactive front on the weather chart is to indicate the boundary of the opposing air masses. Additionally, it displays the location of potentially unfavorable flying weather. The warm air mass may gradually become moister and lead to the formation of clouds and precipitation in the frontal zone. In many cases the inactive front only has a shift in the wind direction and a change in the temperature and pressure.

DESCRIBE the parameters that define fog

Fog Definition Visible layer of condensed moisture. Base at or within 50 feet of surface. Greater than 20 feet thick. Reduces visibility to less than ⅝ mile. Must meet all three conditions to be fog. Two types of fog Radiation Advection

DEFINE the standard atmosphere

For a standard reference, a concept called a standard day is used. In aviation, everything is related to standard day conditions at sea level, which are 29.92 in-Hg (1013.2 mb) and 15° C (59° F). In the lower atmosphere, and thus for most aviation applications, a 1000 foot increase in altitude will result in a pressure decrease of approximately 1 in-Hg and a temperature decrease of 2° C. These values are the standard day pressure and temperature lapse rates.

DESCRIBE the use of Low Level Significant Weather Prognostic Charts

Forecast charts depict predicted positions of fronts and pressure centers, as well as forecast weather across the country.

DESCRIBE how frontal lifting creates turbulence

Frontal Turbulence Caused by warm air lifted by cold front. Most severe in fast-moving front. No turbulence in warm front due to little or no lifting.

DESCRIBE the flight conditions associated with an unstable atmosphere

Fronts - Cold Airmass - Cold Turbulence - Rough Visibility - Good Icing - Clear Precipitation - Showery Winds - Gusty Cloud types - Cumulus Unstable - Thunderstorms Towering cumulus clouds Heavy showers Dust devils Rapidly decreasing temperature while climbing

DESCRIBE the flight conditions associated with a stable atmosphere

Fronts - Warm Airmass - Warm Turbulence - Smooth Visibility - Poor Icing - Rime Precipitation - Steady Winds - Steady Cloud types - Stratus Clues to Flight Conditions Stable Temperature inversions Wide spread fog or low clouds Rising or slightly decreasing temperatures while climbing

DESCRIBE the flight conditions associated with the stratosphere

Generally smooth with excellent visibility. The general lack of weather in this layer makes for outstanding flying.

DESCRIBE ground icing hazards

Ground Icing Hazards Frost usually found first thing in morning. Remove prior to flight. De-icing fluids highly corrosive. Should not be sprayed down intakes or other openings. Other Ground Hazards Taxiing through mud, slush, or water. Splashed on aircraft surfaces. Can freeze later at higher altitudes and colder temperatures. Runway braking conditions Hazardous to control during braking of aircraft

DESCRIBE the aviation hazards of ash clouds

Hazards Multiple engine malfunctions Flameout All engines affected on multi-engine aircraft. Pitted windscreens Affecting cockpit visibility Sandblasting of external surfaces

DESCRIBE the use of Pilot Weather Reports (PIREPs)

IWRUM - IFR differs - Wind Shear - Requested - Unusual Conditions - Missed Approach Pilot Weather Reports (PIREPs) are a valuable source of information used to supplement ground station weather observations Air traffic facilities are required to solicit PIREPs whenever the following conditions are reported or forecasted: ceilings at or below 5000 feet, visibility at or below 5 miles, thunderstorms and related phenomena, icing of a light degree or greater, turbulence of moderate degree or greater, and wind shear. All pilots are urged to cooperate and promptly volunteer reports on these conditions, and any other conditions pertinent to aviation, such as: cloud bases, tops, and layers; flight visibility; precipitation; visibility restrictions; winds at altitude; and temperatures aloft. Pilots are required to submit a PIREP under the following conditions: In-flight when requested When unusual or unforecast weather conditions are encountered When weather conditions on an IFR approach differ from the latest observation When a missed approach is executed due to weather When a wind shear is encountered on departure or arrivaldi

DESCRIBE the effects of temperature deviations from the standard lapse rate on aircraft altimeters

If the air is colder than the standard atmosphere, the aircraft will be lower than the altimeter indicates. If the air is warmer than standard, the aircraft will be higher than the altimeter indicates.

DESCRIBE displayed data METARs

METARs, found on the METARs tab on the ADDS website, are scheduled observations taken between 55-59 minutes past the hour and used in flight planning to determine areas of IFR/VFR and to determine the minimum ceilings en route. METARs are available in both graphic and textual form. To view the graphic presentation, you would click on the desired region on the U.S. map. Reporting stations are depicted on the chart using station models discussed in earlier lessons.

DESCRIBE the effects of pressure changes on aircraft altimeters

If the altimeter is not adjusted and your flight path takes you into an area of lower MSL pressure the aircraft will be lower than the altimeter indicates. Conversely, if your flight path takes you into an area of higher MSL pressure, the aircraft will be higher than the altimeter indicates. When flying from one locale to another a change in pressure of 1.0 in-Hg will change the altimeter reading 1000 feet. Rule: High to Low, Look Out Below The aircraft is lower than indicated, thus the indicated altitude is higher than the aircraft. > Higher Pressure to Lower Pressure MSL = Assigned Altitude (-) Altitude Error AGL = MSL (-) Field Elevation Indicated Altitude on Deck = Field Elevation (+) Altitude Error Rule: Low to High, Plenty of Sky The aircraft is higher than indicated, thus the indicated altitude is lower than the aircraft. > Lower Pressure to Higher Pressure MSL = Assigned Altitude (+) Altitude Error AGL = MSL (-) Field Elevation Indicated Altitude on Deck = Field Elevation (-) Altitude Error

DEFINE indicated altitude

Indicated altitude is the altitude read directly from the altimeter.

DEFINE the types of altitudes

Indicated altitude: As read on altimeter Absolute altitude: Above ground level (AGL) True altitude: Above Mean Sea Level (MSL) Pressure altitude: Above Standard Datum Plane Density Altitude: Not a height reference

DESCRIBE the types of engine icing

Induction Icing Also known as inlet icing. Clear skies and above freezing temperatures. Taxi and departure Reduced pressures in intake system. Lowers temperature Condensation Ice formation High probability with air temperatures +10° C or less and high relative humidity. Compressor Icing Forms on compressor inlet guide vanes. Both induction and compressor icing restrict airflow and could FOD engine.

DESCRIBE the jet stream

Jet Streams Narrow band of strong winds found below the tropopause Average height: 30,000 feet MSL. May be above or below depending on latitude and season Speed: 100 - 150 knots May reach speed in excess of 250 knots Location Position of jet stream changes daily Changes weather patterns Aircrew considerations Head/tail wind Turbulence

LIST the intensities of turbulence used in Pilot Reports (PIREPs)

LMSE Light - Momentary slightly erratic changes Altitude Attitude Pitch Roll Yaw Slight strain against seat belts and shoulder straps. Unsecured objects displaced slightly. Moderate Turbulence - Larger changes in altitude and/or attitude. Variations in indicated airspeed. Definite strain against seat belts and shoulder straps. Unsecured objects dislodged. [Moderate] Reaction: Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult. Severe - Large abrupt changes in altitude and/or attitude. Large variations in indicated airspeed. Unsecured objects tossed about. Aircraft may be momentarily out of control. Extreme - Aircraft violently tossed about. Control difficult or impossible. Possible structural damage. Declare Emergency. Exit area ASAP

DESCRIBE land breezes

Land breeze comes from land at night At night, the circulation is reversed so that the air movement is from land to sea, producing an offshore wind called the land breeze (Figure 2-10). The sea breezes are usually stronger than the land breezes, but they seldom penetrate far inland. Both land and sea breezes are shallow in depth, and their existence should be considered during takeoff and landing near large lakes and oceans.

DESCRIBE the characteristics of the troposphere

Layer adjacent to the earth's surface Large amounts of moisture and condensation Nearly all weather occurs there. Height: 28,000 feet over poles 55,000 feet over equator Temperature normally decreases with altitude (lapse rate). Winds increase with altitude.

DESCRIBE the four principal cloud groups

Low Clouds Characteristics Surface to 6500 feet AGL Serious hazard due to cloud base proximity to terrain Types: Stratus - steady precipitation Cumulus - showery precipitation Middle Clouds Characteristics Bases form between 6500 feet and 20,000 feet AGL Usually light form of precipitation Prefix "Alto" Types: Altostratus - light steady precipitation Altocumulus - light showery precipitation High Clouds Characteristics Base form above 20,000 feet AGL Composed of ice crystals Produce no icing or precipitation Prefix "cirro" Types: Cirrocumulus Cirrostratus Cirrus Special Clouds Characteristics Cumulonimbus clouds are towering thunderstorm clouds with extensive vertical development Nimbostratus clouds build downward Types Cumulonimbus - heavy showers Nimbostratus - violent/heavy steady precipitation The height of the cloud base, not the top, determines the classification. A cloud with a base at 5000 feet AGL and a top at 8000 feet AGL is classified as a low cloud. Each group is subdivided by appearance. There are two principal cloud forms: 1. Cumuliform - A lumpy, billowy cloud with a base showing a definite pattern or structure. 2. Stratiform - A cloud with a uniform base, formed in horizontal, sheet-like layers.

DESCRIBE the weather conditions associated with various clouds

Low Clouds Characteristics Surface to 6500 feet AGL Serious hazard due to cloud base proximity to terrain Types: Stratus - steady precipitation Cumulus - showery precipitation Middle Clouds Characteristics Bases form between 6500 feet and 20,000 feet AGL Usually light form of precipitation Prefix "Alto" Types: Altostratus - light steady precipitation Altocumulus - light showery precipitation High Clouds Characteristics Base form above 20,000 feet AGL Composed of ice crystals Produce no icing or precipitation Prefix "cirro" Types: Cirrocumulus Cirrostratus Cirrus Special Clouds Characteristics Cumulonimbus clouds are towering thunderstorm clouds with extensive vertical development, Nimbostratus clouds build downward Types Cumulonimbus - heavy showers Nimbostratus - violent/heavy steady precipitation

DESCRIBE the factors that influence frontal weather

MCSSS (Marine Corp Save Salty Sailor) 1. The amount of moisture available (shown by the dew point) 2. The degree of stability of the lifted air 3. The slope of the front 4. The speed of the frontal movement 5. The contrast in the amounts of temperature and moisture between the two air masses.

DESCRIBE the recommended procedures for flying through turbulence

Maintain PCL setting consistent with desired turbulent air penetration airspeed. Trim aircraft for level flight. Do not chase airspeed deviations with power corrections. Severe turbulence causes large rapid variations. Allow altitude to vary; do not chase altimeter. Vertical gusts cause significant altitude deviations. Maintain pitch and bank by reference to attitude indicator.

DESCRIBE how mechanical turbulence develops

Mechanical Turbulence Caused by passage of wind over obstructions. Buildings Irregular terrain/ mountains Strength and magnitude dependent on Wind speed Roughness of terrain Stability of the air Mechanical turbulence results from wind flowing over or around irregular terrain or other obstructions. When the air near the surface of the Earth flows over obstructions, such as bluffs, hills, mountains, or buildings, the normal horizontal wind flow is disturbed and transformed into a complicated pattern of eddies and other irregular air movements (Figure 4-2). An eddy current is a current of air (or water) moving contrary to the main current, forming swirls or whirlpools. One example of mechanical turbulence may result from the buildings or other obstructions near an airfield The strength and magnitude of mechanical turbulence depends on the speed of the wind, the roughness of the terrain (or nature of the obstruction), and the stability of the air. Stability seems to be the most important factor in determining the strength and vertical extent of the mechanical turbulence. When a light wind blows over irregular terrain, the resulting mechanical turbulence has only minor significance. When the wind blows faster and the obstructions are larger, the turbulence intensity increases and it extends to higher levels.

DESCRIBE the signs and hazards associated with microbursts

Microbursts - An intense, highly localized downward atmospheric flow with velocities of 2000 to over 6000 feet per minute. Outflow produces wind shears of 20 to 200 knots. Area only ¼ to 2 ½ miles wide Lasts only 5-10 minutes Emanates from cumuliform cloud not a thunderstorm. Microburst Sequence 1 - Normally occur mid-afternoon during summer months. Large vortex ring of air flows outward from center of the downburst. Shaft of rain makes flow visible. Microburst Sequence 2 - May also form dry microbursts. Forms when there's a large temperature (dew point) spread at the surface. Rain evaporates as it descends (virga), which cools the air. Colder air accelerates as it descends. Microburst Damage - Strong winds destructive to ground objects. Many aircraft mishaps have been attributed to microbursts. Takeoff During Microburst - When first entering a microburst, edge of vortex ring produces wind blowing upward from ground. Increase in headwind causes IAS to jump upward rapidly. In center of downdraft, aircraft will begin to descend, but soon enter other side of outflow. Headwind will shift to tailwind, IAS drops rapidly, probably causing aircraft to stall. Landing During Microburst - Natural reaction is to first reduce power and attempt to re-establish descent. Removes power from engine, and wastes valuable time to get aircraft away from ground before entering outflow. _________________________________ Methods of Microburst Detection 1 Visual cues Virga (precipitation that evaporates before reaching the ground) Localized blowing dust Shaft of rain which diverges closer to the ground. Severe thunderstorms Heavy rain Low or no visibility Gusty winds Frequent lightning Tornado activity Methods of Microburst Detection 2 Ground-based Doppler radar Detects Microbursts Tornados Low-level wind shear Real time hazard reporting.. Low level shear alert systems Measures wind speed and direction at ground locations. Compares readings to central sensor. Not real time - after the fact identity Methods of Microburst Detection 3 Pilot Weather Reports (PIREPs) Encountered unusual and unforecast weather conditions. Wind shear encountered on departure or arrival. Definitive information not real time Departure or arrival weather reports Gusty winds Heavy rains or thunderstorms

IDENTIFY the procedures to minimize or avoid the effects of icing

Minimizing Icing Effects Avoid areas of known or forecast icing. Avoid clouds and precipitation at temperatures between 0° and -20° C. Especially at low altitudes over mountainous terrain Minimize bank angle and high AOA Increased stall speed Climbing may alleviate icing conditions associated with warm fronts. Do not fly parallel to a front in icing conditions. Maximizes exposure time to icing. Remove ice or frost prior to takeoff. Avoiding Icing Icing conditions Visible moisture 0° to -20° C At low altitude or mountainous terrain Two options when encountered Climb Out of visible moisture To colder temperature Frozen moisture not an icing hazard. To warmer temperature If below warm front or temperature inversion. Descend Out of visible moisture Below freezing level If visible moisture or freezing level on surface, descending not an option. Anti-Ice/De-Ice Anti-Ice Prevents icing De-Ice Removes existing ice. Three types of anti-ice/de-ice equipment Fluid Lowers freezing point of water. Ground fluids sprayed on aircraft. Prevent or remove icing. In-flight fluids Pumped onto aircraft surfaces to prevent icing. Mechanical Rubber bladders on leading edge of airfoils. Expand and contract Prevent ice buildup Most common on thick-winged aircraft. Heat Increases aircraft surface temperature. Anti-icing or de-icing Electrically Hot air bled off engine

DESCRIBE mountain winds

Mountain breeze Flow down mountain slopes at night Air is cooled by outgoing land radiation and becomes more dense than surrounding air Denser air flows downhill Rising air cools and creates a circulation At night, the air in contact with the mountain slope is cooled by outgoing terrestrial radiation and becomes denser than the surrounding air. As the denser air flows downhill, from the top of the mountain, it is called the mountain wind, and a circulation opposite to the daytime pattern forms.

DEFINE obscuring phenomena

Obscuring Phenomena Visibility reported obscured When reduced less than 7 miles. Cause reported Depending on phenomenon, visibilities can differ greatly in same location with different points of view. Types of phenomena: Fog Haze Smoke Rain and drizzle Snow Blowing snow, dust, or sand

DEFINE the terms used to report turbulence with respect to time

Occasional - Less than 1/3 Intermittent - 1/3 to 2/3 Continuous - more than 2/3

DEFINE relative humidity

Percentage of water vapor in air compared to the maximum amount the air could hold at that temperature Another measure of atmospheric moisture is the relative humidity (RH), which is the percent of saturation of the air. The air can become saturated (RH = 100%) by one of two ways. If the air is cooled, the falling air temperature decreases the dew point spread closer to zero, while the RH rises closer to 100%. If evaporation occurs, this adds moisture to the atmosphere, increasing the dew point, which again lowers the dew point spread and increases the RH. Once the dew point spread reaches 4° F, the RH will be 90%, and the water vapor will begin to condense into fog or clouds. Any further cooling or evaporation will produce precipitation, as there will be more water present in the air than it can hold.

EXPLAIN and identify gradient winds and Buys Ballot's Law with respect to the isobars around pressure systems in the Northern Hemisphere

Pressure Gradient force and Coriolis force balance to create flows Parallel to isobars Clockwise around Highs Counterclockwise around Lows Gradient winds Found above 2000 feet AGL While the pressure gradient force causes air to flow from high pressure to low pressure across the isobar pattern, another force acts upon the wind to determine its direction. The Coriolis force, created by the Earth's rotation, diverts the air to the right-with respect to its initial direction of motion-regardless of whether the air is near a high or a low pressure system. The result of these two forces is the gradient winds, which flow perpendicular to the pressure gradient force. This also means that gradient winds flow parallel to the isobars (Figure 2-6), and the resulting circulation flows clockwise around highs, and counterclockwise around lows. Finally, gradient winds are found above 2000 feet AGL. Buys Ballot's Law, A Rule Of Thumb A rule of thumb to help remember the direction of the wind in relation to a pressure system is Buys Ballot's Law. This law states that if the wind is at your back, the area of lower pressure will be to your left. When standing on the Earth's surface, the low will be slightly forward or directly left because the winds flow across the isobars.

DEFINE atmospheric pressure

Pressure exerted on the surface by the atmosphere due to the weight of a column of air directly above that surface. Always decreases with altitude.

EXPLAIN how radar can aid a pilot when flying in the vicinity of thunderstorms

Radar Detection NEXRAD (Next Generation Radar) Most accurate means of tracking thunderstorms. Scale indicates wind intensity or speed. Television shows Doppler composite. Direct relationship exists between: Strength of radar echos Presence of aircraft icing Intensity of turbulence Height of tops of CBs indicate thunderstorm severity. Airborne Radar Used to circumnavigate and avoid scattered thunderstorms. Not for thunderstorm penetration Severe clear air turbulence and hail can be experienced between thunderstorms.

DESCRIBE weather data on NEXRAD

Radar data is available from the 26th OWS web site by clicking on the "Radar SCNTRL" link in the Weather Preview section. Next Generation Radar (NEXRAD) images provide an excellent source of weather information for pilots. The computer monitor image seen in a weather office is a computer-generated compilation of radar data transmitted from a radar site. NEXRAD presentations show precipitation levels in the area scanned by the radar system. The NEXRAD does not measure the rate of precipitation directly; rather, it measures the energy return from the precipitation particles. The image seen on the screen is actually a computer-generated compilation of returned energy shown in varying colors. This display is referred to as the reflectivity presentation. The intensity of precipitation can be determined by using the graduated scale shown in the legend area of the screen. The maximum radar return strength at the time of the presentation is listed above the scale. This is measured in "dbz," or strength in decibels, of the energy received by the radar. Through use of this scale, precipitation strength can quickly be deciphered for a given area by comparing the color of the area to the color-coded legend. Higher precipitation levels are farther down the color scale. During flight planning, a pilot should carefully analyze the higher intensity areas in relation to the planned route of flight or operating area. Other unique features of the NEXRAD provide the capability to display areas of tornadoes, hail, wind shear, and microbursts. This type of information is particularly useful in planning a flight around known areas of potentially dangerous weather conditions.

DESCRIBE the two main types of fog

Radiation Fog Caused by nocturnal radiation cooling. Rate depends on Surface composition Vegetation Cloud coverage Ceiling Light winds Dissipation begins as sun warms surface. Advection Fog Warm moist air moves over cool surface. At or near saturation Cool surface reduces temp/dew point spread. Usually forms over water. Brought inland by winds. Winds can be stronger. Very thick layer Only wind shift can dissipate. Persistent

DESCRIBE how jet streams are examples of wind shear turbulence

Rapid change of wind speed short distance from core. Vertical shear more significant than horizontal. Exit by turning south or changing altitude.

STATE the requirements for fog formation

Requirements Conditions required for formation of fog. Condensation nuclei High moisture content Small temperature/dew point spread Near equal (saturation) Light surface winds 1 - 10 knots

DESCRIBE the characteristics of a warm front

SE to SW, warmer, falls then rises, front NE movement, 15kts, stratiform, smooth turbulence, red color Wind Shift — Warm front wind shifts are not as sudden as those of a cold front, and therefore, turbulence isn't likely. The wind generally shifts from SE to SW Ceiling and Visibility — The widespread precipitation ahead of a warm front is often accompanied by low stratus and fog. In this case, the precipitation raises the moisture content of the cold air until saturation is reached. This produces low ceilings and poor visibility covering thousands of square miles. Ceilings are often in the 300 to 900-foot range during steady, warm frontal rain situations. Just before the warm front passes the station, ceilings and visibilities can drop to zero with drizzle and fog. The worst conditions often occur in the winter when the ground is cold and the air is warm; the best scenario for dense fog and low ceilings. Turbulence and Thunderstorms — If the advancing warm air is moist an unstable, altocumulus and cumulonimbus clouds can be embedded in the cloud masses normally accompanying the warm front. These embedded thunderstorms are quite dangerous, because their presence is often unknown to aircrews until encountered. Even with airborne radar, it can be difficult to distinguish between the widespread areas of precipitation normally found with a warm front and the severe showers from the embedded thunderstorms. The only turbulence along a warm front would be found in such embedded thunderstorms. Otherwise, little to no turbulence exists in warm front systems. Precipitation and Icing — Approaching an active warm front from the cold air side (from the east), precipitation will begin where the middle cloud deck is from 8000 to 12,000 feet AGL. Often, this precipitation will not reach the ground-a phenomenon called virga. As you near the front, precipitation gradually increases in intensity and becomes steadier. Occasional heavy showers in the cold air beneath the frontal surface indicate that thunderstorms exist in the warm air aloft. Drizzle, freezing drizzle, rain, freezing rain, ice pellets (sleet), and snow are all possible in a warm front, depending on the temperature. The shallow slope and widespread thick stratiform clouds lead to large areas of icing. It may take a long time to climb out of the icing area, and you may need to descend into warmer air to avoid the icing.

DESCRIBE the conditions associated with a cold front

SW to NW, Colder, Falls then rises, front SE movement, 20kts, Cloud types cumuliform, rough turbulence, blue color, good visibility, gusty winds Wind shifts — Expect an abrupt wind shift when passing through a frontal zone, especially when flying at lower altitudes. Turbulence is often associated with the wind shift. The wind generally shifts from SW to NW with greater speeds behind the front. Ceiling and visibility — If an active cold front moves at a moderate or rapid speed (15-30 knots), its weather zone is generally less than 50 miles wide. If the front moves slower, its weather zone may be broad enough to seriously affect flight operations for many hours. Ceilings and visibilities are generally visual meteorological conditions (VMC), but isolated instrument meteorological conditions (IMC) exist in heavy precipitation and near thunderstorms. Wider areas of IMC conditions can exist in winter due to snow showers. Turbulence — Many active cold fronts have turbulent cloud systems associated with them, but thunderstorms may not always be present. Even when there are no clouds, turbulence may still be a problem. As a rule, expect a rough flight in the vicinity of an active cold front, even when flying at a considerable altitude. Precipitation and icing conditions — Active cold fronts usually have a relatively narrow belt of precipitation, especially if the precipitation is showery. Icing may be severe in cumuliform clouds. Slow-moving cold fronts may have a broader area of precipitation and a greater threat of remaining in icing conditions for a longer period. Thunderstorms and squall lines — Severe weather is implied to exist in areas of reported thunderstorms. Chapter 4 will detail the hazards associated with thunderstorms.

DESCRIBE weather data on satellite imagery

Satellite images are also available from the 26th OWS web site by clicking on the "Satellite SCNTRL" link in the Weather Preview section. For general-purpose use, there are two types of satellite imagery available. When combined they provide a great deal of information about clouds to a pilot. Through interpretation, one can determine the type and height of clouds as well as the temperature and the thickness of cloud layers. From this information, the pilot can get a good idea of possible associated weather along the planned route of flight.

DESCRIBE sea breezes

Sea breeze comes from sea during the day During the day, the pressure over the warm land becomes lower than that over the colder water. The cool air over the water moves toward the lower pressure, replacing the warm air over the land that moved upward. The resulting onshore wind, blowing from the sea, is called a sea breeze, with speeds sometimes reaching 15 to 20 knots (Figure 2-9).

DESCRIBE the three characteristics of precipitation

Showers - starts, stops, changes intensity rapidly, associated with cumuliform clouds Continuous - steady, changes intensity gradually, associated with stratiform clouds Intermittent - stops, starts at least once during the hour, showers or steady, cumuliform or stratiform clouds

STATE the letter identifiers of each of the In-Flight Weather Advisories

Sierra - sucky weather Airmet (widespread IFR, less than VFR conditions over 50% of the area or extensive mountain obscuration) Tango - turb. moderate (widespread area 3000sq mile area) or sustained surface winds > 30kts Zulu - Icing moderate (over 3000sq mi)

DESCRIBE the sky coverage terms that define a ceiling

Sky Coverage and Ceilings Sky Coverage Reported in eighths Height of cloud bases given in hundreds of feet AGL. Ceiling Height above ground (AGL) Lowest broken or overcast layer Vertical visibility (VV) into an obscuring phenomenon. Obscurations Vertical visibility (VV) is distance seen directly upward from the ground into a total obscuration. Used when sky is totally hidden. Base within 50 feet of surface. Hazardous Reduces slant range visibility Referred to as indefinite ceiling.

DESCRIBE the characteristics of the stratosphere

Smooth flying conditions Excellent visibility Constant temperature to approximately 66,000 feet Temperature slowly increases with altitude (above 66,000 feet). Few aircraft can fly in Stratosphere. Average top height over USA 158,000 feet MSL

DESCRIBE the types of atmospheric stability

Stable - Tendency to return toward initial condition when disturbed Neutrally stable - System has tendency to remain in its new state after being disturbed Unstable - System has tendency to move away from its initial condition when disturbed Stable Air Colder than the surrounding air after being lifted Settles when lifting is removed Neutrally stable air Same temperature of the surrounding air after being lifted Remains at the same place until acted upon by something else Rare but same results as stable Unstable air Warmer than the surrounding air after being lifted Lifted air continues to rise after the lifting force is removed due only to the parcel's warmer temperature

DIFFERENTIATE between sea level pressure and station pressure

Station pressure is the atmospheric pressure measured directly at an airfield or other weather station. Sea Level Pressure (SLP) Pressure at mean sea level (MSL) Measured directly at sea level. Calculated if the station is not at sea level. Used for surface analysis charts.

DESCRIBE the cloud formations associated with mountain wave turbulence

Strong winds blowing perpendicular to a mountain range. Form standing waves Turbulence can be in clear air as well as in clouds. Clouds best way to determine if turbulence present. Rotor Cloud - Form downwind from and parallel to mountain range. - Cylindrical shape - Downward flow has been known to reach the ground. Cap Clouds - Cover top of mountain - Remain stationary Lenticular Clouds - Form on leeward side of mountain from standing waves Local Intensities Rule of thumb for turbulence proximity/intensity With 50 knots wind at altitude of peak - EXTREME Up to 150 miles downwind - SEVERE Up to 300 miles downwind - MODERATE It is possible for wave action to take place when the air is too dry to form clouds, producing CAT. Still, cloud forms particular to wave action provide the best means of identifying possible turbulence, aside from weather forecasts and PIREPs. Although the lenticular clouds in Figure 4-4 are smooth in contour, they may be quite ragged when the airflow at that level is turbulent. These clouds may occur singularly or in layers at heights usually above 20,000 feet. The rotor cloud forms at a lower level and is generally found at about the same height as the mountain ridge. The cap cloud usually obscures both sides of the mountain peak. The lenticular clouds (Figure 4-4), like the rotor and cap clouds, are stationary in position, even though the wind flows through them. Extreme turbulence is usually found at low levels on the leeward side of the mountain in or near the rotor and cap clouds when the winds are 50 knots or greater at the mountaintop. With these wind conditions, severe turbulence can frequently be found to exist from the surface to the tropopause and 150 miles downwind. Moderate turbulence can be experienced often as far as 300 miles downwind under those same conditions. When the winds are less than 50 knots at mountain peak level, a lesser degree of turbulence may be experienced. Mountain wave turbulence is dangerous in the vicinity of the rotor clouds and to the leeward side of the mountain peaks. The cap cloud must always be avoided in flight because of the turbulence and the concealed mountain peaks.

DESCRIBE structural icing

Structural icing Forms on external surfaces of aircraft. Icing types: Clear Rime Mixed Frost

EXPLAIN and identify the surface wind direction with respect to the gradient winds in a pressure system in the Northern Hemisphere

Surface winds (below 2000 feet) AGL Friction reduces wind speed Coriolis force shifts wind direction toward isobars New balance of forces Wind blowing across the isobars (45°) CW around Highs CCW around Lows Out of High pressure into Low pressure When we consider winds below 2000 feet AGL, we cannot ignore the role of surface friction in the analysis of wind direction. Surface friction reduces the speed of the wind, which causes a reduction in the Coriolis force. This results in a different set of forces that must be balanced: the PGF, Coriolis force, and friction. When the new balance of forces is reached, the air blows at an angle across the isobars from high pressure to low pressure. This angle varies as a result of the type of terrain, but for our purposes, we will assume a 45° angle (Figure 2-7). Another way to think of this effect is that the Coriolis force still tries to turn the wind to the right, from its initial intended direction of the PGF, but it does not turn to the right quite as much as with gradient winds. Thus, surface winds still move clockwise around highs, and counterclockwise around lows, but since they blow across the isobars at a 45° angle, they also have a component of motion that moves air out of the high pressure and into the low.

DESCRIBE differences in U.S. civil, military, and international TAFs

TAF Differences U.S. civil stations Statute miles instead of meters Include DTG of transmission prior to forecast period May include probability of precipitation When U.S. military stations amend, correct, or have routine delayed forecast, appropriate time appended to last line of forecast

DESCRIBE the discontinuities used to locate and classify fronts

TDs Win Playoffs (Temp, Dewpoint, Wind, Pressure) Differences in the various properties of adjacent air masses-in particular, their temperature, moisture (indicated by the dew point), winds, and pressure-are used to locate and classify fronts. For example, when comparing two dissimilar air masses, one will be colder than the other. Because of this, the colder one will be denser and drier (it must have a lower dew point). Cloud types are also useful indicators of the type of front and will be discussed in connection with each individual front.

LIST the intensities of icing used in Pilot Reports (PIREPs)

TRACE Ice becomes perceptible. Rate of accumulation slightly greater than sublimation. De-icing/anti-icing not used unless encountered for extended time. LIGHT Rate of accumulation can be a problem over extended time (over one hour). Occasional use of de-ice/anti-ice equipment prevents accumulation. Not a problem if equipment used. MODERATE Rate of accumulation potentially hazardous. Even for short encounters De-ice/anti-ice equipment or diversion necessary. SEVERE Rate of accumulation extreme. De-ice/anti-ice equipment fails to reduce or control. Immediate diversion necessary.

DESCRIBE the use of TAFs in flight planning

Terminal Aerodrome Forecasts (TAF) Airport forecast for specific period (usually 24 hours) Used to determine VFR or IFR flight plan requirements TAF contains forecasts of: Wind Forecast visibility Weather/obstructions Sky coverage Icing Turbulence Minimum altimeter setting Pertinent remarks

DESCRIBE the weather data entered on a DD Form 175-1

The DD Form 175-1, Flight Weather Briefing, is prepared and used by the local weather office to brief pilots on weather conditions both locally and along a planned route of flight. The form may be faxed to you by the weather office if a verbal briefing is not desired. Keep in mind the some of the blocks on the form may not be completed, or extra data may be included as an attachment. The following screens will outline the information contained in the form

DESCRIBE the use of Surface Analysis Charts

The Surface Analysis Chart depicts pressure centers, fronts, and barometric pressure lines. The information displayed on the Surface Analysis Chart is observed weather, meaning that the chart represents past history, and is not a forecast. The valid time (VT) of the chart is the observation time of the information that was gathered to compile the chart and is given in Coordinated Universal Time (UTC) at the top right.

DEFINE saturation

The air reaches saturation when it contains the maximum amount of water vapor it can hold for that temperature. Within 4° F, visible moisture Saturation Air is holding the maximum water vapor for: - Temperature - Pressure

STATE the average lapse rate in degrees Celsius

The average or standard lapse rate is 2° Celsius per 1000'

DEFINE a lapse rate

The decrease in atmospheric temperature with increasing altitude is called the standard lapse rate (troposphere). Isothermal lapse rate (stratosphere) Temperature constant with increasing altitude. Inverted lapse rate (temperature inversion) (stratosphere) Temperature increases with increasing altitude.

DESCRIBE the relationship between air temperature and dew point temperature with respect to saturation

The dew point can never be higher than the air temperature: only equal to or less than. This spread provides a good indication of how close the atmosphere is to the point of saturation.

DEFINE dew point temperature (TD)

The dew point temperature (TD) is the temperature at which saturation occurs. The dew point is a direct indication of the amount of moisture present in the air. The higher the dew point, the greater chances for clouds, fog, or precipitation. Temperature saturation occurs Higher temperature = more moisture in the air

DESCRIBE techniques for flight in the vicinity of mountain waves

The following techniques should be applied when mountain wave turbulence has been forecast: Avoiding Mountain Wave Turbulence Circumnavigate if possible. Fly 50% higher than peak. Avoid rotor, cap, and lenticular clouds. Approach mountain range at a 45° angle. Avoid strong downdrafts on leeward side of mountain. Pressure changes affect pitot-static instruments. Fly recommended turbulent air penetration speed 1. Avoid the turbulence if possible by flying around the areas where wave conditions exist. If this is not feasible, fly at a level that is at least 50% higher than the height of the highest mountain range along your flight path. This procedure will not keep the aircraft out of turbulence, but provides a margin of safety if a strong downdraft is encountered. 2. Avoid the rotor, lenticular, and the cap clouds since they contain intense turbulence and strong updrafts and downdrafts. 3. Approach the mountain range at a 45° angle, so that a quick turn can be made away from the ridge if a severe downdraft is encountered. 4. Avoid the leeward side of mountain ranges, where strong downdrafts may exist, until certain turbulence is not a factor. 5. Do not place too much confidence in pressure altimeter readings near mountain peaks. They may indicate altitudes more than 2500 feet higher than the true altitude. 6. Penetrate turbulent areas at air speeds recommended for your aircraft.

DESCRIBE the four methods of lifting

The four methods of lifting are convergence, frontal, orographic, and thermal (Figure 2-20). FOCT Convergence of two air masses, or parts of a single air mass, force the air upward because it has nowhere else to go. Frontal - Because of the shape of cold fronts, as they move through an area, they will lift the air ahead of the cold air mass. Orographic lifting is a term indicating that the force of the wind against a mountainside pushes the air upward. Thermal lifting, also known as convective lifting, is caused when cool air is over a warm surface, and it is heightened by intense solar heating.

DESCRIBE the structure of a front

The most significant frontal weather occurs in the lower layers of the atmosphere (<20,000ft). However, the temperature contrast between the air masses can sometimes extend as high as the tropopause. > Fronts are named according to the temperature change they bring > Fronts move across the country with their attached low-pressure system and isobars, as the corresponding air masses move > Every front is located in a trough of low pressure

EXPLAIN the term pressure gradient

The rate of pressure change in a direction perpendicular to the isobars (horizontal distance) is called the pressure gradient, and this isobar spacing represents the size of the pressure gradient force (PGF). The PGF is steep, or strong, when isobars are close together, and is shallow, or weak, when the isobars are far apart-the steeper the gradient, the stronger the winds. The PGF is the initiating force for all winds. pressure gradient force causes air to flow from high pressure to low pressure. Pressure Gradient Force (PGF) Rate of change in pressure in horizontal distance Perpendicular to isobars Size of pressure gradient represented by isobar spacing Tight spacing → Steep pressure gradient → Strong Pressure Gradient Force → Faster wind speed Wide spacing → Shallow pressure gradient → Weak Pressure Gradient Force → Slower wind speed High pressure results from descending air Creates horizontal diverging force (PGF) Shown via isobars -- out of Highs into Lows Low pressure results from ascending air Creates horizontal converging force (PGF) Into Lows from High

DESCRIBE how thermal turbulence develops

Thermal Turbulence Also called Convective Turbulence. Vertical air movement Result of heating from below. Solar heating Cold air moving over warmer surface. Strength depends on type of surface. Thermal (or convective) turbulence is caused by localized vertical convective currents resulting from surface heating or cold air moving over warmer ground. Strong solar heating of the Earth's surface can result in localized vertical air movements, both ascending and descending. For every rising current, there is a compensating downward current that is usually slower in speed since it covers a broader area. Such vertical air movements can also result from cooler air being heated through contact with a warm surface. The turbulence that forms as a result of heating from below is called thermal, or convective, turbulence. The strength of convective currents depends in part on the extent to which the earth's surface has been heated, which in turn, depends upon the nature of the surface (Figure 4-1). Notice in the illustration that dry, barren surfaces such as sandy or rocky wasteland and plowed fields absorb heat more readily than surfaces covered with grass or other vegetation, which tend to contain more moisture. Thus, barren surfaces generally cause stronger convective currents. In comparison, water surfaces are heated more slowly. The difference in surface heating between land and water masses is responsible for the turbulence experienced by aircrews when crossing shorelines on hot summer days. When air is very dry, convective currents may be present even though convective-type clouds (cumulus) are absent. The upper limits of the convective currents are often marked by haze lines or by the tops of cumulus clouds that form when the air is moist. Varying surfaces often affect the amount of turbulence experienced in the landing pattern and on final approach.

DESCRIBE the hazards associated with thunderstorms

Thunderstorm Development Four requirements for thunderstorm development are: Moisture Unstable air Lifting action Building through the freezing layer Once lifted air has reached the point where it will continue to rise freely, the cumulus cloud can grow rapidly and form cumulonimbus clouds. Lifecycle of a T-Storm 1. Cumulus- Updrafts 2. Mature- Updrafts, Downdrafts and Hazards 3. Dissipating- Downdrafts and Hazards Extreme Turbulence - Can cause changes in altitude. Can cause structural damage. Extra stress on the airframe. Effect depends on severity of turbulence and aircraft speed. Extreme turbulence is the most severe hazard associated with thunderstorms. Gust Front - Forms on the surface at the leading edge of an advancing thunderstorm. Cause low level W.S. and Ex. turb Roll and Wall Clouds - Roll clouds and wall clouds occur in severe and fast moving thunderstorms. Indicate the presence of low level wind shear and extreme turbulence. Hail - Circulate in updrafts and downdrafts. Hailstones larger than one-half to three-quarters of an inch can cause significant damage to aircraft in a few seconds. Hail has been encountered: As high as 45,000 feet in clear air Carried 10 to 20 miles downwind. Lightning and Electrostatic Discharge - Results from separation of positive and negative charge, from water and ice passing in up and down drafts Lightning Hazards - Static charge builds up in the aircraft while in the clouds. Can strike aircraft flying in the clear. Structural damage is possible. Catastrophic fuel ignition possible. Pilots can experience flash blindness. Static buildup sometimes released through St. Elmo's fire. Tornado - Violent destructive whirling wind accompanied by a funnel shaped cloud. Damage and effects documented in television and news reports. Cloud types: Tornado touches ground. Funnel cloud - not touching surface. Waterspout - touches water surface.

DESCRIBE the recommended techniques for avoiding thunderstorm hazards

Thunderstorm Hazard Avoidance Circumnavigate isolated thunderstorms. Over the top Avoids most hazards. Altitude margin for turbulence and hail (at least 1000 feet higher for every 10 knots of wind speed at cloud top level) Underneath Not in the worst of hazards Altitude margin - ⅓ distance from ground to cloud base Penetrate lower ⅓ of storm. Thunderstorm Common Sense Don't takeoff or land if a thunderstorm is approaching. Don't fly into a cloud mass containing embedded thunderstorms without airborne radar. Avoid flying under a thunderstorm, even if you can see through to the other side. Thunderstorm Penetration Procedures Penetrate perpendicular to minimize time in storm. Penetrate the storm below the freezing level or above the -20° C level. Minimum altitude should be 4000 to 6000 feet AGL above the highest terrain. Establish recommended turbulent air penetration airspeed. Expect significant deviations in attitude and altitude. Disengage the autopilot. Avoid abrupt control inputs to prevent pilot-induced structural damage. Secure all loose objects. Tighten lap belt and lock shoulder harness. Turn cockpit lights up to highest intensity to lessen dangers of temporary blindness from lightning. Turn on pitot heat.

DESCRIBE the characteristics of the tropopause

Transition zone between troposphere and stratosphere. Identified by abrupt change in lapse rate. Frequently find turbulence, contrails, and haze. Average height over USA 36,000 feet MSL. Jet stream winds occur just below tropopause.

(Chapter 4) LIST the classifications of turbulence used in Pilot Reports (PIREPs)

Turbulence is any irregular or disturbed flow in the atmosphere producing gusts and or eddies. Turbulence classified by causative factors. (WTF Man) Wind shear, Thermal, Frontal, Mechanical

STATE the standard units of pressure measurement

Units of measurement Inches of mercury (in-Hg) Millibars(mb) Hectopascal (hPa)

DESCRIBE valley winds

Valley winds Flow out of valley during day Air heats and rises Air cools and settles back in valley In the daytime, mountain slopes are heated by the Sun's radiation, and in turn, they heat the adjacent air through conduction. This air usually becomes warmer than air farther away from the slope at the same altitude, and, since warmer air is less dense, it begins to rise (Figure 2-11). It cools while moving away from the warm ground, increasing its density. It then settles downward, towards the valley floor, completing a pattern of circulation (not shown in Figure 2- 11). This downward motion forces the warmer air near the ground up the mountain, and since it is then flowing from the valley, it is called a valley wind.

DEFINE the types of visibility

Visibility Ability to see and identify. Prominent unlighted objects by day Prominent lighted objects at night Expressed in Statute miles Hundreds of feet Meters Flight Visibility Average forward horizontal distance from cockpit. See and identify. Prominent unlighted objects by day Prominent lighted objects at night Measured in statute miles Prevailing Visibility Greatest horizontal visibility Equaled or exceeded throughout over half horizon circle. Measured in statute miles. Need not be continuous. Slant Range Visibility Distance on final approach at which runway environment in sight. May be reported by PIREP. Can be estimated by meteorologists. Runway Visual Range (RVR) Horizontal distance seen by looking down runway from approach end. Reported in meters or hundreds of feet

STATE the requirements for the formation of structural icing

Visible moisture Super-cooled water droplets Liquid water at air temperatures below freezing Clouds most common form Free air temperature and aircraft's surface temperature below freezing.

DESCRIBE icing conditions associated with fronts

Warm Front Stratiform clouds Rime icing Low rate of accumulation Widespread area of icing Cold Front Cumuliform clouds Clear Icing High rate of accumulation Limited area of icing Frontal Icing - Occluded Front Mixed clouds Stratus and cumulus Mixed icing Rime, clear, and mixed Rapid and heavy accumulation Very widespread area of icing

DESCRIBE the conditions associated with a stationary front

Wind shift 180, Temp change either, falls then rises, no movement, 0 to 5 kts, stratiform clouds, smooth, R&B Stationary front has a 180° wind shift. The wind shift may be from any one direction to the opposite direction, as stationary fronts are less likely to be aligned in any one particular direction. The weather conditions occurring with a stationary front are similar to those found with the warm front, but are usually less intense. The weather pattern of a stationary front may persist in one area for several days, until other, stronger weather systems are able to push the stationary front weather along its way.

DESCRIBE the use of Winds-Aloft Prognostic Charts

Winds-Aloft Prognostic Charts are available at the Winds/Temps tab on the ADDS website. These charts present the observed and average forecast flight level winds aloft.

DESCRIBE the use of Winds-Aloft Forecasts

Winds-Aloft driving force for what altitude you choose. Notice that all temperatures are negative above 24,000 feet as indicated in the heading information by the phrase "TEMPS NEG ABV 24000." At these altitudes, all the digits are run together, eliminating the redundant minus sign between the wind and the temperature. For example, 251744 forecasts a wind from 250° T at 17 knots with a temperature of -44° Celsius A direction of "99" indicates a variable wind direction. When forecast wind speeds are less than 5 knots, direction is difficult to determine, and the winds are called "light and variable," and the code "9900" will be listed. If winds are forecasted to be 200 knots or greater, the wind group is coded as 199 knots. For example, 8299 would be decoded as 320° T at 199 knots or greater. Wind information is never forecast for altitudes within 1500 feet of the surface. Temperature information is never forecast within 2500 feet of the surface. Temperature information is never forecast for the 3000-foot level.