GL 18 Weather patterns

difference bw a warm front occlusion and an cold front occlusion

1. a cold front occlusion occurs when the overtaking cold front is colder than the air that the warm front is displacing 2. warm front occlusion is more likely to produce severe weather

adiabatic process info

1. as air rises, the pressure decreases and the airmass expands and cools 2. the temp. of an airmass changes without gaining or losing heat from the surrounding air 3. as air descends, its pressure increases, and it becomes warmer as it is compressed

what characteristics apply to low clouds

1. base ranging from 0 to 6,500 ft agl 2. most consist of water

temperature inversion hazards

1. can trap weather and pollutants 2. restrict visibliity 3. contribute to formation of fog, haze, or low clouds, when inversion is near the ground.

which describes a cold front

1. fast moving cold fronts are pushed by high pressure behind them 2. slow moving cold fronts have a shallow leading edge that produces clouds behind the surface front 3. cool, dense air of a cold front forces the less dense, warmer air upwards

characteristics of clouds with vertical development

1. instability 2. bases found at altitudes assoc with low clouds 3. bases found at altitudes assoc with middle clouds

how does a temperature inversion form?

1. on nights when the ground cools and lowers the temperature of the adjacent air 2. when cool air is forced under warm air 3. when warm air spreads over cold

characteristics of a stationary front

1. separate two airmasses that might not move for several days, and display a mix of the weather characteristics of both warm and cold fronts

cold front characteristics

1. separates an advancing mass of cold, dense, and stable air from a warmer, lighter, less stable airmass 2. is accompanied by severe turbulence, strong winds, and precipation cool, dense air of a cold front forces less dense, warmer air upward. cumuliform clouds and showers are common near cold fronts. fast moving cold fronts: > are pushed by intense, high pressure systems behind the front > have steep leading edge and extreme discontinuites that makes them more hazardous than slow moving cold fronts slow moving cold fronts: > have a shallow leading edge > are less hazardous than fast moving cold fronts. >produce clouds that extend far behind the surface front cold fronts approach quickly and can change ewater completely within a few hours

what causes upslope fog to form

1. sloping landmasses, moist, stable air, windw

characteristics of a warm front

1. steady precipitation with little turbulence usually precedes a warm front 2. warm fronts occur when warm air replaces cooler air 3. stratus clouds usually extend out ahead of a slow moving warm front 4. slope of warm front is gradual

how does temp. of the surface modify an airmass?

1. when an airmass moves over a cool surface, vertical movement is inhibitied, and the airmass stabilizes 2. when an airmass moves over a warm surface- vertical air movement develops, resulting in instability

temp and dewpoint converge at approx ___ degree fahrenheit per 1,000 ft of alt

4.4.

upslope fog

> develops along coastlines or mountain valleys near lakes > requires wind to form > develops when winds force moist, stable air up a sloping land mass

advection fog

> exists most commonly along coastline under cloudy skies > requires light wind to form > develops when wind moves a low layer of warm, moist air over a cooler surface any time light winds move warm, moist air over a cooler surface, conditions are ideal for advection fog.

characteristics of vertical development clouds (cumuloform clouds)

Cumuliform clouds always indicate atmospheric instability they form in convective currents as the heating of the earth's surface lifts unstablce moise air. the convective currents also produce turbulence. bases of clouds with vertical development form at altitudes assoc with low or middle clouds. unstable conditions build these clouds vertically when other cloud formation obscure vertically developed clouds, they are referred to as embedded clouds 3 types of clouds can display vertical development: 1. cumulus clouds- puffy white dome shaped with flat bases. indicate a shallow layer of instability and although they cause turbulence, they cause little icing or precipitaion 2. towering cumulus clouds look like mounds of cotton with cauliflower tops. their color can very from brilliant white at top to gray near bottom. indicate deep areas of unstable air. contain moderate to severe turbulence with icing and often develope into thunderstorms 3. cumulonimbus clouds are thunderstorms. they are gray white or black with lots of moisture and present may flying hazards

what conditions cause radiation fog to form

Flat, low-lying surfaces, calm, humid nights, high pressure systems

test: which form of precipitatin is composed of droplets .02 inch or greater that fall at a steady rate and stop gradually?

RAIN

atmosphere is most UNSTABLE when the air is ______ and ______

WARM AND MOIST

fog is ___

a low cloud that forms a base not more than 50 ft agl

amt of moisture air is capable of holding depends on ____

air temp

what is the process of adiabatic heating

as air descends, it compresses, and becomes warmer

characteristics of high clouds

bases of high clouds develop above 20,000 ft agl. mainly ice crystals but seldom pose turbulence or icing hazards high cloud family contains 3 basic types of clouds: 1. cirrus clouds are thin wispy clouds that form above 30,000 ft AGL. they can serve as a warning of approaching bad weather 2. Cirrostratus clouds are long bands or sheets of thin, white clouds against a deep blue background. they have low moisture content and pose no icing hazard 3. cirrocumulus clouds- white, patchy clouds resembling cotton. they can produce light turbulence.

characteristics of middle clouds

bases of middle clouds develop at 6,500 ft AGL, and the tops extend to about 20,000 ft AGL middle clouds are composed of water, ice crystals, or supercooled water. they can cause moderate turbulence and severe icing hazards middle cloud family contains two basic cloud types: 1. altostratus clouds are flat, dense clouds that cover a wide area. they are gray or gray white and although they produce minimal turbulence, they can cause icing hazards 2. altocumulus clouds are patchy gray or white clouds that form when altostatus clouds break up. they can contain supercooled water droplets and can produce light turbulence

what characteristics apply to middle clouds

bases ranging from 6500 to 20,000 ft agl composed of water, ice crystals, or supercooled water

characteristics of high clouds

begin at 20,000 ft agl

why is temp inversion hazardous to pilots

causes poor visibility

four families of clouds

cloud families are distinguished by their characteristics and their altitudes. 1. low clouds are made of droplets of liquid water and develop between ground level and about 6,500 feet AGL 2. middle clouds are made of liquid water droplets, ice crystals, or supercooled water droplets and develop bw 6,500 ft and 20,000 ft agl. These clouds pose turbulence and icing hazards 3. high clouds are usually composed of ice crystals and develop above 20,000 ft agl vertical development clouds start as low as middle clouds, but they build vertically because of convection Latin words are used to describe cloud characteristcs. for ex. "nimbus produce rain

Cloud formation

cloud formation process involves three events 1. air cools to its dewpoint and becomes saturated. 2. water vapor collects around condensation nuclei 3. condensation changes water vapor into clouds or fog. the difference bw temps and dewpoint is referred to as the temperature/dewpoint spread a small temp/ dewpoint spread indicates that clouds or fog are liley to form

precipitation

coalescence: water droplets collide and merge condensation: water droplets grow until they fall deposition: ice crystals form directly from water vapor ice crystal procees: ice crystals get water from evaporating supercooled droplets

what causes steam fog to form

cold, dry air, warm water surface

clouds form when air cools to its dewpoint and ___ occurs

condensation

what causes rain drops to develop and grow until they are heavy enough to fall from cloud

condenstation

causes of temperature inversion

condition in which the air temp. increases with altitude. Two factors cause temp. inversions 1. the ground cools and lowers the temp of the adjacent air. 2. a frontal system forces cool air under warm air or warm air over cold air temp inversions develop in smooth, stable air. if wind blows into the area, it mixes the air enough to break up any inverstion

the atmosphere is most STABLE when the air is ____ an ____

cool and dry

conditions that cause advection fog?

cool surfaces, light wind, warm, moist air

airmass modification

degree to which airmass changes depend on several factors, including temp difference bw the airmass and new surface. stable airmasses display : 1. generally smooth air 2. layered or stratiform clouds 3. widespread areas of clouds, steady rain, or drizzle when an airmass moves over a warmer surface, its lower layers are warmed from below, causing vertical movement ad instability. when airmass flows over a cooler surface, its lower layers are cooled from below and airmass stabilizes moisture content of an airmass affects the characteristics it acquires as it moves from source region prolonged cooling from below causes the air to cool to its dewpoint, forming low clouds or fog that can persist for weeks.

steam fog

develops when cold, dry air moves over warmer water, which evaporates and rises steam fog is composed entierely of water droplets that can freeze quickly and fall as ice particles, posing icing hazards because it forms in relatively unstable air, low-level turbulence is assoc with steam fog.

condensation occurs when the temperature and ____ are equal, forming dew, fog, or clouds

dewpoint. frost forms under same conditions as dew at freezing temps.

precipitation stuff:

drizzle- distinguished by very small droplets and commonly associated with fog or low stratus clouds virga- evaporates before it reaches the ground, creating the appearance of streaks hanging in the air rain- composed of droplets .02" or greater which fall to the ground precipitation induced fog- forms when evaporation from falling precipitation saturates the cool air

moisture is present in atmosphere in 3 states: 1. solid 2. Liquid 3. gas name the 6 processes that cause moisture to change state

each time moisuter changes physical state, it releases or absorbs energy. latent heat is the amt of heat energy required to change the state wo change its temp. there are 6 processes that cuase moisture to change state 1. evaoporation changes liquied water into water vapor when water absorbs latent heat 2. condensation change vapor into liquid when wator vapor releases latent heat 3. sublimation changes ice directly into water vapor when ice absorbs latent head 4. deposition- changes water vapor directly into ice when water vapor releases lanten heat 5. melting gradually changes ice into water when ice crystals absorb latent heat. 6. freezing changes water into ice when water releases latent heat

what process changes liquid water to water vapor

evaporatin

characteristics of low clouds

extend from near surface to about 6,500 feet AGL consist of liquid water droplets suspended in air. they might contain supercooled water droplets, which pose icing hazards low cloud family had 3 cloud types: > stratus clouds are layered clouds that form as the earth cools the moist air above it or when moist, stable air flows up sloping terrain. Gray uniform clouds. >nimbostratus clouds are grey or black. these low clouds can be several thousand feet thick and pose serious icing risks >stratocumulus clouds are white, puffy clouds formed when status layers break up or cumulus clouds spread out

a low cloud that forms a base not more than 50 ft agl is known as

fog

what hazards do temperature inversion cause pilots

fog, poor visibility, haze

what type of inversion forms when cool air is forced under warm air or when war air spread over cold

frontal inversion

effects of frost on aircraft

frost forms when air is saturated and surface temp is below freezing. Deposition changes water vapor directly into ice crystals on freezing surfaces. frost is a serious hazard because it interferes with the smooth airflow over the wings and can cause early airflow separation, resuling in a loss of ligt. Frost increases drag and weight, which, when combines with the loss of lift, can prevent an aircraft from becoming airborne at normal takeoff speed Federal air regs (FAR) require that your plane is free of frost before you attemp to fly (FAR 91.527)

how does frost affect performance of a plan

frost on airplane reduces lift and increases drag

what coud family has base beginning at 20,000 ft agl

high

this cloud family is usually made of ice crystals

high clouds

humidity and relative humidity

humidity describes amount of water vapor in the air. relative humidity- describes how close the air is to saturation at the current temperature

how is humidity different from relative humidity

humidity is the actual amt of water vapor in the air; relatve huidy is how close the air is to saturation

what causes ice crystals to form as water vapor evaporates from super cooled water droplets

ice crystal process

how is snow formed from water vapor

ice crystals are formed by deposition

in a temperature inversion, temperature _____ as altitude increases

increases

causes of precipitation

is a liquid or solid water particle that falls from atmosphere water and ice particles grow until the atmospher can no longer support them, and then they fall from the cloud processses that create precipitation: 1. condensation forms water droplet that cont to grow until they fall from cloud 2. deposition causes ice crystals to form directly from water vapor and grow until they are heavy enough to fall from a cloud 3. coalescence occurs when water droplets of different sized collide and merge until they are large enough to fall from the cloud 4. ice crystals process causes ice crystals to acquire evaporating water vapor from supercooled water droplets. during the ice-crystal process, ice crystals form directly from water vapor and grow until they fall.

the rate at which temp of an airmass decreases as alt increases is

lapse rate

airmass

large body of air that: 1. contains uniform temp and moisture 2. acquires the overall characteristics of its source region. 3. spans a few thousand miles and exists for several days to more than a week an ideal source region is a large area that contains uniform geography and temp. - most conducive area: over vicinity of large desert. mid latitudes get mixed around too much to be ideal for creating airmasses airmasses are classified according to characteristics of the regions over which they form: > continental airmasses are developed over land and are typically dry > maritime airmasses develop over large bodies of water and contain large amt of moisture > polar airmasses develop over polar regions and have cool temps > tropical airmasses develop near tropics and have warm temps > continental polar airmasses orginate over polar land masses and contain cold, dry, stable air > maritime tropical airmasses originate over water and contain warm, moist, unstable air moist unstable air causes the formation of cumuliform clouds that produce showers and turbulence but result in good surface visibility

hail

large clumps of ice. wwater freezes in upper cloud levels. as the freezing droplets start to fall, they collide and increase in size. strong updrafts return them to higher cloud level where they collide with other ice pellets and get bigger. hailstones can grow into large ice chunks and be serious flight hazards

which cloud family extends from surface up to 6,500 ft agl and is composed mainly of water droplets

low clouds

what is fog

low lying cloud that can form thick layers close to ground. typically forms as soon as temp of air approaches its dewpoint its base i no more than 50 ft AGL ground fog does not extend very high above the surface

at what alt do the bases of vertical development clouds form

low to middle

what process changes ice to water

melting

what cloud family can be composed of water, ice crystals, and supercooled water, and has a base as low as 6,500 ft agl

middle

cloud stuff

middle clouds- contain liquid water droplets, ice crystals, or supercooled water droplets that can form ice on your plane high clouds- have bases above 20,000 agl and are usually made of ice crystals low clouds- contain small droplets of liquid water and develop bw groun level and about 6,500 ft AGL middle clouds- contain liquid water droplets, ice crystals, or supercooled water droplets that can form ice on your place

stationary fronts

opposing forces bw warm and cold airmasses are balanced and move very slowly stationary fronts: 1. separate 2 airmasses that might not move for several days 2. display a mixture of the weather characteristics of both warm and cold fronts

an airmass formed from a source region of cold air near south pole is classified as

polar

rain

precipitation- classified as rain when it is .02 inches or greater in diameter. it falls at a steady rate and stops gradually. rain showers- start suddenly, change intensity suddenly, and stop suddenly drizzle- very small droplets that are less than .02 inches in diameter warm rain and drizzle can develop into dense precipitation induced fog freezing rain and freezing drizzle freeze upon contact with objects sometimes falling rain evaporates very quickly and never reaches the ground. this is called virga if rain falls through a temp. inversion, it can freeze and arrive at ground level as ice pellets

what forms when evaporation from falling precipitatino saturates the cool air

precipitation- induced fog

phases of warm fronts

prior to: light rain, drizzle, sleet, snow. visibility poor. cold to col temp. dewpoint rises steadily and pressure falls. during: light drizze, poor visibiliyt, wind is variable, rising temp, steady dewpoint and pressure becoming steady after: precipitation decreases to rain showers if any, visibility is fair in haze, temp warming, then steady, dewpoint, rising then steady, pressure slight rise. the calm after the storm!

phases of occluded front

prior to: light to heavy rain. poor visibility. air temp depends on if it is a cold or warm one. during: nimbostratus. possible towering cumulus and or cumulonimbus. visiblity poor. temp : cold occlusion: falling and warm occlusion : rising dewpoint- slight drop. pressure becoming steady after: precipitation- light to moderate, then clears. visibility is improving. temp for cold : colder for warm: milder dewpoin is rising then steady then pressure has slight drop however may rise after passage of warm occlusino

cold front phases

prior- light showers and steady wind. high dew point and falling pressure with pretty good visibility during passage- rain becomes heavy. maybe thunder. lighting .wind is gusty. visibility is poor. temp at dewpoint drops. pressure bottoms out and then rises rapidly. after passage - rain showers dissipate and visilibyt is good. temp. cont to cool . dewpoint cont to drop and pressure cont. to rise

what type of fog forms on clear, calm, humid nights over flat, low-lying surfaces

radiation fog

how can you distinguish ran or snow from a rain or snow shower

rain or snow falls at a relatively steady rate and stops gradually. showers start suddenly, change intensity suddenly, and stop suddenly.

lapse rate.-

rate at which air temp decreases with increased altitude. average lapse rate = 2 degrees Celsius per 1,000 ft actual lapse rate varies, and determines stability of atmosphere lapse rate used to predict stability of atmosphere . expressed as degrees per thousand feet. measures av. temp change as an airmass rises/ descends.

____ is how close the atmosphere is to saturation ___ is the actual amt of water vapor in the air

relative humidy; humidity

snow

snow forms when temps are below freezing and temp of air and dewpoint converge. ice crystals form by deposition and grow quickly as they acquire the water vapor that is evaporating from supercooled water droplets. ice crystals must become heavy enough to fall from the cloud as snow. snow falls at a relatively steady rate and stops gradually. snow showers start suddenly, change intensity suddenly and stop suddenly. snow grains are the solid equivalent of drizzle. very small, white, opaque particles of ice. different from ice pellets cuz flatter and neither shatter nor bounce when they strike ground . fall streaks are similar to virga, but ice particles change from ice into vapor as they fall. transformation of ice crystals directly into vapor as they fall is sublimation

how do temp and moisture affect atmospheric stability

stability decreases as heat and moisture in the air increase

adiabatic processes

stability is the atmosphere's resistance to vertical motion. to understand you must understand the following : Adiabatic cooling and adiabatic heating causes the temp of an airmass to rise or fall without exchanging heat with the surrounding air. remember atmosphere has layers. Pressure of the upper layers of the atmosphere compresses the layers below them. In the process of adiabiatic cooling 1. air rises and pressure decreases 2. air expands and cools in adiabatic heating: 1. air sinks and pressure rises 2. air compresses and the temperature rises

what type of fog forms when cold, dry air moves over warmer water

steam fog

what process changes ice directly into water vapor

sublimation

Effect of temp and moisture on stability

temp and moisture influence atmospheric stability and resulting weather : 1. dry air is usually stable, and weather is usually clear. in dry air, the adiabatic lapse rate is 3 degrees celsius per 1000ft 2. moist air causes more vertical motion and more dynamic weather than dry air. moist adiabatic lapse rate is 1.1- 2.8 degrees celsius 3. warm, moist air is least stable, and resulting weather can include precipitation and thunderstorms.(think of the tropics)

what is dewpoint

temp at which air reaches saturation and can hold no more water vapor

the discontinuities encountere in a front are ___, wind, and barometric pressure

temperature

dewpoint

tempt at which the air reaches saturation and can hold no more water vapor. dewpoint and temp. are proportional: the higher the air temp, the higher the dewpoint.

lapse rate is

the rate at which the temp. of an airmass decreases as altitude increases

formation of temperature inversions

there are 2 types of temp inversions: 1. terrestrial radiation inversions (radiation cooling) occur near the ground on clear, still nights. affects only the air within a few hundred ft of the surface. 2. frontal inversions - occur when cool air is forced under warm air (cold fronts) or when warm air spreads over cold air (warm fronts).

if temp increases with alt. instead of decreasing with alt

this is temp inversion

calculating cloud base

use knowledge of temp and dewpoint to figure out where clouds may form. roughly estimate the alt clouds may develop

characteristics of warm fronts

warm air overtakes and replaces cooler air. less severe weather assoc. tends to remain in region for days. moves slower so slope of warm front is grdaul warm air can extend for several hundred miles ahead of the front cirrostratus, altostratus and stratus clouds often precede a slow moving warm front. cumulus an stratocumulus clouds can develop alond, ahead of, and behind the front steady precipitation with little turbulence usually precedes a warm front. Warm fronts can remain in a region for days and influence weather

how does hail form

water droplets freeze and begin to fall, but strong updrafts carry them upward within the cloud, where they grow larger. after repeated trips up and down, they become too heavy for the updrafts to lift and fall from the cloud

to form hail what must happen first

water droplets freeze in clouds that are exposed to strong updrafts

what conditions are necessary for cloud formation

water vapor, cooling, condensation nuclei

characteristics of fronts

when airmasses leave their source regions, they come into contact with other airmasses with diff. characteristics. these are called discontinuities. the boundary that separates discontinuous airmasses is called a front three major frontal discontinuities influence weather: 1. a change in temp. 2. shift in wind direction or speed 3. a decrease in pressure at the boundary of the fronts frontal discontinuities across fronts can pose serious hazard to flight.

how does snow form

when temperatures are below freezing and the air temperature and dewpoint converge snow forms when deposition forms ice crystals

characteristics of occluded fronts

when warm front and cold front converge and cold front overtakes the warm 1. cold front occlusions - occur when fast moving cold front is colder than slow moving warm front. forces warm front aloft 2. warm front occlusions- when qwarm frontal occlusion lists, moist, unstable air. get more severe weather. when cold frontal occlusion lifts moist, stable air, weather is a mix bw warm and cold front

how does upslope fog develop

wind forces moist, stable air up a sloping land mass

what conditions cause advection fog

wind moving a low layer of warm, moist air over a cooler surface