Block 2: RADAR
standard pressure levels
200mb: 11,790 meters/36680feet 300:9160meters/30050 feet 500: 5570meters/18270feet 700: 3010 meters/ 9875 feet 850:1460meters/4790feet 925: 760 meters/ 2,490 feet
blizzard conditions
A combination of high surface winds and accumulated snow cover or concurrent snowfall Use forecast techniques/methodology for heavy snowfall and/or strong surface winds. Forecast blizzard conditions where potential for high winds with significant blowing snow that will reduce surface visibility below ½ mile will occur.
hodograph
A graphical tool which depicts the environmental vertical wind shear. From a vertical wind shear profile, the observed wind at each level can be plotted as a vector arrow drawn from the center of the diagram. They are then connected to form the hodograph—the longer the hodograph, the greater the vertical wind shear. Supercells are typically associated with environmental wind profiles represented by clockwise curving hodographs. Winds increase with height and shift from southeasterly near the surface to southwesterly or westerly at 700mb. The shape of the hodograph alone is not always sufficient to determine the potential for storm rotation in a given wind profile. Consider helicity, which is calculated for you, in conjunction with the shape. Helicity of at least 150m2 for optimal tornadogenesis. In the absence of at least some instability, helicity is essentially meaningless
Isodrosotherm
A line connecting points of equal dewpoint temperature. Isodrosotherms are analyzed with an interval of 2°, 5°, or 10° Celsius or Fahrenheit.
isobar
A line connecting points of equal pressure. The normal interval for isobars is 4 mb, using a base value of 1,000 mb.
isotherm
A line connecting points of equal temperature. Isotherms are often analyzed with a 2° or 5° Celsius or Fahrenheit interval.
Isotach
A line connecting points of equal wind speed. Isotachs are typically drawn with an interval of 10, 20, or 40 knots.
Standard Deviation
A measure of a spread of values used to find whether the average of a value is representative. The closer sets of numbers are to each other the more consistent they are
surface wind roses
Allows a user to generate a monthly plot of wind speed and direction in a circular plot for a particular location. Speeds are displayed for every 10 degrees of direction and is color coded. Note the period of record a the top—the longer the period of time, the more accurate the data is.
500 mb
Areas of negative and positive vorticity, as well as negative and positive vorticity advection, are most commonly analyzed at 500 mb. This level is also known as the steering level, as most storm systems follow the winds at 500 mb. An overview of vorticity is provided below. Vorticity can be described in terms of clockwise or counterclockwise spin. Negative vorticity is associated with an anticyclonic (clockwise) spin, such as a ridge or high pressure system, and is marked with an 'N'. Positive is associated with a cyclonic (counterclockwise) spin, such as a trough or low pressure system, and is marked with an 'X'.
grid point
Assigns values for the atmospheric variables at a series of grid points in space and time. An analysis field is derived by smoothing the initial conditions and often incorporating forecast conditions that were obtained from a previous forecast.
Level III data product list
BR = Base Reflectivity BV = Base Velocity SRV = Storm Relative Velocity SW = Spectrum Width ET = Echo Tops VIL = Vertically Integrated Liquid OHP = One Hour Precipitation STP = Storm Total Precipitation ZDR = Differential Reflectivity CC = Correlation Coefficient KDP = Specific Differential Phase HCA = Hydrometeor Classification Algorithm DOD = One Hour Difference DSD = Storm Total Difference
PRODUCT LIST
Base reflectivity (BR) Base velocity (BV) Storm relative velocity (SRV), Spectrum width (SW) Echo tops (ET) Vertically integrated liquid (VIL), VIL density (VILD) Probability of severe hail (POSH) Maximum expected hail size (MEHS).
rules of thumb for non convective severe wind
Based on synoptic patterns, upper air parameters, topography and climatology 700mb Maximum Wind Band Used in conjunction with 850mb low-level jet Used to determine strength and location of potential for strong winds. Identify all maximum wind bands of ≥30kt Draw maximum wind band using an arrow on the downwind end
Characterization unit
Characterization units must be prepared to continue mission-essential functions without significant interruption during a national security emergency or other disruptive conditions, such as major equipment/communications outages or evacuations. To ensure continuity of operations during these situations, units will develop processes to use alternate equipment/systems, operate from alternate locations, or arrange transfer of critical functions to other organizations. Units aligned to provide continuity of operations support for another unit must be capable of providing the support and be fully prepared to assume the responsibility in minimum time. Characterization units will: Establish and formally document continuity of operations processes and procedures. Provide a copy of the continuity of operations documents to all organizations tasked to provide backup support. Make continuity of operations documents available to supported units upon request IAW parent MAJCOM policies and procedures. Review and update continuity of operations processes and procedures, consistent with MAJCOM continuity of operations policies or as necessary, to reflect substantive changes in operations. Exercise continuity of operations processes quarterly. Real world events meet this requirement if properly evaluated and documented, to include lessons learned.
climate
Climate is the average or collective state of the earth's atmosphere at any given location or area within a specific period.
Narratives
Climatology studies that describe conditions in a specified region, country or location. These studies are in the narrative, or written, form and are a syntheses of information available on the climate. Most are full year studies, but some cover only part of the year and a few are very short overviews. There are two basic types, text-only versions and graphics-included .pdf version. All .pdf studies cover the full year.
contour
Contours are drawn only on upper-level charts, and take two forms. Isallohypses are lines of equal height change over some period of time. Isoheights are lines of equal height.
descriptive/ regional climatology
Deals with the climates of geographic regions based on analyzed statistics from a particular area.
exploitation unit
EUs at main operating locations (garrison operations) will establish an AOL to continue providing mission-essential functions to parent/host unit activities. EUs at expeditionary locations will establish AOL procedures as quickly as the tactical situation permits. EU leaders will coordinate with supported agencies to select an appropriate location and secure the needed communications and other specified resource requirements. At a minimum, EUs will establish communication from the AOL with the local ATC facility, command post, primary installation customers, and the supporting CU. See AFMAN 15-111, Surface Weather Observations for applicable observing duties at a back-up location
alternate operating location AOL
EUs responsible for preparing surface weather observations, without regard to the mode of operation, will establish an AOL when the primary location is evacuated. EUs will work with the local command to establish an AOL and outline what is needed from various agencies on the installation to support operations at the location. Operations at the AOL and any reciprocal support from other agencies will be coordinated and formally documented in base/host unit plans or a local weather support document. See AFMAN 15-129, Volume 2, Air Force Weather Operations - Exploitation, for additional guidance on operating at an AOL. The AOL will be a location with adequate communications and a view of the airfield complex. Some EUs may be equipped to augment the AMOS at the AOL, assuming the AMOS sensors are still working. If the sensors are not operating, or there is no interface available to augment the AMOS, EUs should plan to use available back-up equipment (e.g., deployable equipment) and methods to prepare the observation. Within 15 minutes of arrival at the AOL, weather technicians will complete and transmit an augmented observation. The "eyes forward" function will begin as soon as practical after the observation is transmitted. Note: Observation is not required at automated locations if AMOS is working properly and no mandatory supplementary criteria are occurring. At a minimum, weather technicians must be able to prepare an initial observation containing the minimum required elements (i.e., wind speed and direction, prevailing visibility, present weather and obscurations, sky condition, temperature, dew point and altimeter setting). Mandatory elements may be omitted from the observation if the necessary equipment is not available. Resume normal observing operations (i.e., automated, augmented) upon return to the primary observing location.
notorious wind boxes
Empirical rules that identify favorable synoptic conditions for well known areas of strong wind gusts in the CONUS
panel back round display
Ensure the background is enabled (via GIS->Show Background). Increasing levels of detail will become apparent as you zoom into the display
physical climatology
Explains the cause of climate by the physical processes influencing and producing different kinds of physical climates such as marine, desert, mountain, etc
point ensemble probability bulletins
Green is 0-9% Yellow is 10-49% Red is 50-100% Use for general timing and indication of significant change—the PEP should be used mostly as an ensemble of suggestions. Go further in to the model data to get the hard facts your forecast is looking for.
tornado forecast tools
Hodographs The SPC Supercell Composite Parameter (SCP) The SPC Significant Tornado Parameter (STP) The 4km AFWA Mesoscale Ensemble Prediction Suite (MEPS)
freezing precipitation
Ice particles which fall through a warm layer, melt, and refreeze upon surface objects with below freezing temperatures. Occurrence is relatively rare compared to other types of precipitation. Highly dependent on vertical temperature structure of air mass in which it occurs. Requires a shallow subfreezing surface layer, above freezing, moist layer aloft and a subfreezing layer above the warmer air.Use of location specific thickness values, thickness, temperature, and dewpoint nomograms Tracking existing areas of freezing precipitation on radar Skew-t, current and forecast Model output, graphical and numerical Cross section products (moisture, temperature and thickness) on NTFS Plotting/overlaying pertinent current atmospheric parameters on a single chart
200 and 300mb analysis
It is wise to focus on the 300 mb level during the winter, 200mb during summer Jet streams Are the product of, and are situated above, horizontal temperature gradients Stronger in the winter Analyzed on weather maps using isotachs two most significant jet streams are the polar front jet and the subtropical jet
K index
K-Index is only used to determine the potential for convection. When the 850mb dew point is high and the 700 mb dewpoint depression is low (indicative of abundant moisture), the second term in the equation becomes large, inflating the K-index. Higher K-index could also point toward the potential for heavy rainfall and increased lightning potential. less than 25=low 26-39=moderate 40+=high
island barrier effects
Lee Side Clearing is formed by forced subsidence on the lee side of mountains. Indicates winds crossing ridgeline > 45º. Plumes often form when the wind speed is too slow or too fast for Karman vortices to form or when an island is not high enough to disturb the flow. Islands tend to form cloud plumes, which are long, narrow, low stratocumulus cloud lines, and are good indicators of the surface wind direction. Plumes, which can extend for hundreds of miles downstream, are produced by turbulent vertical motion produced as a result of an island in a fairly strong low-level flow capped by an inversion.
jet streaks
Localized wind speed maximum embedded within a jet stream Can exceed 150 knots Air entering a jet streak speeds up, while air leaving a jet streak slows down. This results in regions of upper-level convergence and divergence. A jet streak on the right side of a trough causes the trough to lift out and weaken, while a jet streak on the left side of a trough causes the trough to dig and deepen.
Engineering Weather Data EWD
Many times civil engineering will contact a forecaster for climatological data. Engineering Weather Data is a collection of climatological products used by professional engineers in the design, construction, and maintenance of buildings. Included are data on wind, moisture, solar radiation, rain rate, heating and cooling days, snow load and freeze thaw cycles as outlined in AFI 32-1163. The EWD is easily generated via the 14th WS webpage. A large file with a plethora of climatology data will be created, and can easily be shared with anyone needing the information
850 mb
Often used to determine areas of low-level warm and cold air advection Tightly spaced isotherms indicate a strong temperature gradient and increase the rate of temperature advection, given that the winds are also strong. Similar to the 700 mb level, moisture analysis can also be performed at 850 mb. Another type of jet stream, the low level jet, can also be found at 850 mb. Fronts may also be apparent at 850 mb. Cold fronts and warm fronts should be analyzed on the warm side of temperature gradients.
open cell cumulus
Open-cell CU generally forms over water behind cold fronts. It forms into SC as it moves overland. Associated with cyclonic or straight line flow and a good indicator of strong CAA in cyclonic flow. Low level wind flow tends to parallel this cyclonic shape. On visible imagery, has a chicken-wire appearance, consisting of open and closed ringlets of CU with clear centers. In strong low-level winds, these ringlets will become distorted and line up. Ringlet's shape is associated with wind speed
700 mb
Particularly useful for locating the positions of shortwave troughs and ridges Look for shortwave troughs and ridges and associated areas of warm and cold air advection. Compare with other levels to determine the strength of low pressure systems. Strong areas of low pressure exhibit a negative tilt (tilt back with height). The regions of greatest height falls and rises indicate how the weather pattern may change with time. Specifically, troughs will propagate toward areas of height falls, and ridges toward areas of height rises. A surface low will deepen if a shortwave trough approaches to within 6° of the low. The 700 mb level also provides a good measure of midlevel moisture: look for regions with a low temperature/dewpoint spread (low dewpoint depression). A low dewpoint depression at 700 mb is often an indication of deep moisture. Shortwave troughs lie in the regions of greatest cyclonic turning, while shortwave ridges lie in the regions of greatest anticyclonic turning. A shortwave trough is denoted with a solid bowed line, and a shortwave ridge is denoted with a zigzag line. Warm air advection is typically found on the right side of a shortwave trough axis, with cold air advection on the left side. The opposite is true for shortwave ridges.
polar front jet
Polar front jet most significant jet stream caused by low-level temperature gradients in the mid-latitudes, generally in the vicinity of 60° N to 40° N important because it provides the dynamics that drive mid-latitude extratropical cyclones These cyclones can produce significant winter storms during the cold season and severe thunderstorm outbreaks during the spring and summer. However, the position of the jet varies seasonally, shifting north during the summer and south during the winter. The jet's elevation also varies from around 200 mb during the summer to 300 mb during the winter. Forecasters should keep this in mind when performing upper-air analyses.
vorticity advection
Positive vorticity advection (PVA) is the advection of higher values of vorticity into areas of lower vorticity often, but not always, associated with upper-level divergence, upward vertical motion, height falls, increasing instability, and precipitation potential found in the right rear and left front quadrants of jet streaks. Negative vorticity advection (NVA) is the advection of lower values of vorticity into areas of higher vorticity associated with upper-level convergence, downward vertical motion, height rises, increasing stability, and fair weather. found in the left rear and right front quadrants of jet streaks.
VCP
Shows the Volume Coverage Pattern (VCP) for the current product. The VCP determines how often a complete volume is produced VCP Volume Frequency: 12... every 4.4 minutes 11, 121... every 5 minutes 21... every 6 minutes 31, 32... every 10 minutes
PROD
Shows the time the currently selected product was created.
VST GR2
Shows the volume scan time of the current product. It ties together all of the products for a given volume. When Live polling is enabled, different tilts of a given product may have different VST times because GR2Analyst incrementally downloads the Level II data for the current volume scan.
tornadogenesis
Supercell TS occur within environments characterized by: Ample low-level moisture Sufficient CAPE Deep-layered vertical wind shear Significant forcing mechanism Required for Tornadogenesis in supercells: A persistent rotating updraft A rear-flank downdraft
SPC significant hail parameter
Takes into account Most unstable CAPE Mixing ration of most unstable CAPE parcel 700-500mb lapse rate 500mb temperature 0-6km shear Values greater than 1 represent a favorable environment for significant hail. Hail that is 2.5" in diameter or larger is often associated with SHIP values of 2.0 to 3.0.
SPC significant tornado parameter
Takes into account factors known to contribute to environments favorable for significant tornadoes (EF2 or greater). 0-6km bulk wind difference 0-1km storm relative helicity Surface parcel CAPE Surface parcel CIN Surface parcel LCL height There is an enhanced risk of significant tornadoes when the STP is greater than 1.0
meps
The AFWA 4km MEPS on AFW-WEBS outputs the probability of at least 1 tornado within 20nm, 10nm, and 4km (2.5nm) of a point. The model algorithm first uses a parameter called updraft helicity to determine the probability of a supercell. Updraft helicity is an explicit measure of updraft rotation. In general, when updraft helicity values are greater than 50m2s-2, it is likely that a supercell is present. MEPS also produces a severe weather threat summary, which highlights areas where the probability of a tornado within 20nm is greater than 5%. because only a relative small percentage of supercells actually produce tornadoes, the algorithm tries to discriminate between supercells that are likely to produce tornadoes and those that won't. The discriminating predictors are LFC and the wind speed at 5km level. LFC heights between 500m and 2500m are conducive to tornadoes. The maximum 5km wind speed allowed is 30m/s-1and the minimum is 10m/s-1. The maximum tornado probability allowed is 50% because probabilities exceeding this threshold are beyond the skill of the algorithm.
absolute
The extreme highest and lowest values recorded at the place of observations.
extreme
The highest value and the lowest value for a particular meteorological element that has occurred over a particular period. Usually applied to months, seasons, or years
mean or average
The mean is the most commonly used climatological parameter. The sum of all the values divided by the number of values.
frequency
The number of times a certain value occurs within a specified period
TDWR sites
The primary advantage of TDWR over previous radars is that it has a finer range resolution—meaning it can see smaller areas of the atmosphere and it is good for the detection of hazardous wind shear conditions. The reason for the resolution is that the TDWR has a narrower beam than traditional radar systems and it uses a set of algorithms to reduce ground clutter
surface analysis
The surface analysis will feature the greatest concentration of observations, due an extensive network of reporting stations. Surface fronts, troughs, ridges, high and low pressure systems, temperatures, relative humidities, dewpoints, and wind speeds & directions can all be analyzed at the surface. All of the same analysis guidelines and tips apply at the surface as at other levels. Be sure to maintain continuity with other pressure levels, and relate surface and upper-level features in order to gain a complete understanding of the state of the atmosphere.
Lightning climatology
This application enables retrieval of regional lightning climatology maps, which show the geographic and monthly distribution of lightning activity. The summaries are stratified based on 12Z 700mb wind flow at CONUS upper air stations and corresponding lightning activity from the National Lightning Detection Network. Progression of lightning over the day for a given wind sector (and consideration of other conditions favorable for thunderstorm formation), can help a forecaster with that awareness.
TILT
Tilt: Displays the different volume scans avaliable. Note: You cannot use the 3D feature if there are less than 3 scans avaliable.
severe thunderstorm
Tornadoes Convective Winds ≥ 50kt Hail ≥ ¾" in diameter Lightning within 5nm
fronts
Transition zone, or boundary, between air masses of different properties Changes in temperature, moisture, wind direction, pressure, and precipitation cold frontal stack 1-3 degrees warm frontal stacks is 3-6 degrees Cold fronts slope 1 mile in the vertical for every 50 to 150 miles in the horizontal while warm fronts slope 1 mile in the vertical for every 100 to 300 miles in the horizontal
heavy snow
Use climatology/known areas of terrain induced heavy snow occurrences Model Output Synoptic patterns favorable to heavy snow production (ie the lower half of the comma's head in a comma cloud) Jet stream snow bursts Empirical rules/checklists Ensembles Site Rules of Thumb and Forecaster Reference Notes The Cook Index can also be utilized in forecasting for heavy snow. Uses warm air advection at 200mb to forecast snowfall amounts up to 24 hours.
isallobars
Used in determining cold frontal positions, pressure gradient tendencies, speed of surface features
severe weather threat index
Used to determine the potential for severe thunderstorms and is better than other indices because it takes into account the vertical wind profile of the atmosphere.SWEAT Index increases when: Low level moisture is high Temperatures aloft are cool There is substantial vertical wind shear The Total-Totals Index is large less than 150= severe TS unlikely between 150 and 300= slight chance greater than 300 but less than 400= possible greater than 400= likely w tornadoes possible
ensemble forecasting
Using several models, a stochastic framework provides a spectrum of possible forecast solutions. This is accomplished through an ensemble of model runs to produce an envelope of possibilities for the future state of the atmosphere. Therefore providing a more well-informed forecast. Great overview/quick-glance forecasting tool.
heavy rain
Utilize radar signatures and Hourly/Storm Total Precipitation products Model Output Quantative Precipitation Method Ensembles Site Rules of Thumb and Forecaster Reference Notes
spectral
Values are represented as waves with 126 waves used to represent the atmosphere. The equations of the mathematical model are rewritten to express dependent variables as the time-dependent amplitudes of these waves. The equations are solved to find the time rate of change of the amplitudes of these waves, i.e. produce the forecast fields for the atmospheric variables.
VIV process
Verification The first step is to compare a previous run's 12-or 24-hour prognosis to the current 00-hour forecast and note differences. Initialization Deals with only the 00-hour forecast. Compare the 00-hour forecast positions with the analysis by using satellite and other real-time data from the same time to check the forecast for accuracy. Verification or QA The last step of VIV is a quality control check of the first two steps. The forecaster compares the positions of significant features from the 12-hour forecast on the current run to real-time data to see if the model is still doing well, or performing better/worst than during the first two steps.
vertical wind sheer
Vertical wind shear, typically measured in meters per second (m/s), causes thunderstorm updrafts to tilt in the vertical. An appropriate amount of vertical wind shear can increase storm organization and longevity by preventing rain-cooled air in the downdraft from interfering with the updraft. Strong vertical wind shear can also interact with a storm's updraft to enhance it and/or produce mid-level rotation, a defining characteristic of supercell thunderstorms. Generally, vertical wind shear of at least 25 m/s over the lowest 4 to 6 km of the atmosphere is necessary for the formation of a supercell. Other severe thunderstorms, such as bow echoes, can develop when strong shear is confined closer to the ground, such as in the lowest 2 to 3 km of the atmosphere.
warm core barotropic low
Warm core barotropic lows feature warm air throughout the atmospheric column. This results in high thicknesses and corresponding high upper level heights. Some other characteristics of warm core barotropic lows: The low density of the warm air causes low pressure at the surface. Vertically stacked Circulation weakens with height and may become a high aloft Not directly associated with a frontal boundary Often caused by intense surface heating Frequently develop over the desert southwest of the United States during the summer months Tropical cyclones are also warm core barotropic lows.
non convective severe weather
Winds from non-convective sources equal to or higher than 35kt Heavy Rain, 2 inches or more within 12 hours Heavy Snow, 2 inches or more within 12 hours Freezing Precipitation of any type Blizzard Conditions Winds equal to or greater than 30kt Falling or blowing snow restricting visibility to half a mile or less
rope clouds
`very narrow, long, sometimes meandering, cumulus cloud formation that is frequently visible in satellite imagery. It is generally associated with a cold front or a land-sea breeze front and indicates the exact frontal position. It is commonly found over the ocean, often in the Pacific
hodograph
a graphical display of the atmosphere's wind profile, can provide an idea of the magnitude of the speed and directional shears, and what type of thunderstorms to expect: A zigzag hodograph pattern indicates weak shear and the potential for shortlived, single cell thunderstorms. A straight line hodograph indicates a steady increase of winds with height and an environment conducive to multi-cell thunderstorms. A curved hodograph suggests strong speed and directional shear, favorable for supercells. A clockwise curve is associated with right-moving supercells. A counterclockwise curve is associated with left-moving supercells.
occluded front
a typical mid-latitude cyclone, a warm front extends eastward from the low pressure center, with a cold front extending south. Cool air is located ahead of the warm front, with colder air behind the cold front. If the cold front catches up to and merges with the warm front, an occluded front develops. The occluded front now separates the cool air that was ahead of the warm front from the cold air behind the cold front. This is
MOD CURVES
allow users to generate monthly summaries of weather parameters' hourly changes at a chosen location. Displays the diurnal and annual changes of temperatures, dew point, altimeters setting, relative humidity and pressure altitude. Diurnal changes are depicted well this way and generally should only be used as a comparison during high pressure with no changes anticipated. When used correctly, MODCURVES are a great tool for winds, ceilings, temperatures and pressure
OCDS Climograms
are charts derived from the OCDS. When you pull up a station's climograms from the 14th website, a PDF will open with charts for many different weather parameters. Part of Ramstein AB's climograms are viewed to the right, as you can see they are in an easy to read, graphical format. Great for briefings where numerical data would be confusing to the viewer
karman vortices
cloud eddies that form on the lee of islands under condition of a low-level inversion and wind speeds of about10-30 knots. The downwind trail of clouds consists of counter-rotating clouds topped by the inversion.
cold core barotropic high
cold air near the center of the high, and are associated with low thicknesses and low upper level heights. Other characteristics: • Vertically stacked • Anticyclonic circulation weakens with height and may transition to a low aloft • Not directly associated with a frontal boundary • Develop as a result of intense surface cooling • Associated with clear skies and cold temperatures
baroclinic high
derive their energy from temperature gradients. However, unlike a baroclinic low, which develops along a frontal boundary, a baroclinic high develops on the cold side of a boundary. The high develops downstream from an upper level ridge, and intensifies as a result of convergence aloft ahead of the ridge. Baroclinic highs tilt back with height toward warm air.
total tools index TT
determine convective intensity, but it only uses data from two levels and does not take into account CAPE, shear, and inversions. Cannot be calculated at high elevations where 850mb is at or below ground level. greater than 40=TS greater than 42=severe ts possible greater than 48= Severe ts likely greater than 55= severe ts likely tornado possible
Sea breeze
develop 3-4 hours after sunrise and peak in the early afternoon with wind speeds of 8-12 knots. The sea breeze circulation typically extends 12-18 miles in each direction from the coastline. Generally, every 1° F temperature difference amounts to a 1 knot wind speed increase. Common focus area for thunderstorm development
Baroclinic lows
develops along a stationary frontal boundary. As an upper level short-wave trough approaches, divergence aloft causes pressure to fall along the front. Air on each side of the front advects toward the low pressure area to fill it in, while at the same time being deflected to the right by the Coriolis force. This results in a counter-clockwise circulation. As the circulation and short-wave trough interact, temperature advection causes the short-wave to deepen, enhancing vorticity in the base of the trough. This results in continued upper level divergence and deepening of the surface low. Baroclinic lows: • Exhibit strong temperature advection, with warm air advection ahead of the low and cold air advection behind the low. • Tilt back with height (negative tilt), toward the short-wave trough and cold air. This tilt maintains the low by allowing the upper level divergence, described above, to continue. Eventually, the low occludes (becomes vertically stacked), causing it to fill in and dissipate.
Lifted Index (LI)
difference between the observed temperature at 500mb and the parcel temperature at 500mb. The more unstable the environment the more negative the LI. LI does not take into account all environmental factors and should be used in conjunction with other analyses when determining the potential for severe thunderstorms. += stability 0 to -3=marginal instability -4 to -7= strong instability -8 or less= extreme instability
Wind Stratified Conditional Climatology WSCC
enables users to retrieve ceiling and visibility data using a conditional climatology approach. Shows the probability of weather category changes based on nearly identical prior conditions. Displays the historical percentage of time the ceiling and visibility conditions occurred for the chosen month. Best used when a low ceiling and/or visibility is affecting the station and no organized clearing mechanism can be detected.
tornadoes
enhances fujita scale 0=65-85 1=86-110 2=111-135 3=136-165 4=166-200 5=over 200 Essential to the forecast process is analysis of several key environmental parameters: 0-3km wind profile 0-6km wind shear Inflow layer wind speeds 0-3km and 0-1km storm relative helicity (SRH) Effective SRH (ESRH) Magnitude of Convective Inhibition (CIN) Bulk Richardson Number (BRN) Lifting Condensation Level (LCL)
lift
essential for the development of thunderstorms. There are a number of lifting mechanisms with frontal boundaries the most common. Ahead of cold fronts, squall lines may develop. Severe thunderstorms can also develop ahead of warm fronts. In fact, enhanced vertical wind shear and horizontal vorticity in the vicinity of a warm front can create an environment favorable for tornadic supercells. Dry lines can also produce severe thunderstorms. Occluded fronts and sea breeze boundaries also generate adequate lift for thunderstorms, although these storms are not as likely to be severe. Orographic lift, such as air riding up over a plateau or mountain, is also sufficient for thunderstorm development, although again, these storms are not as likely to be severe. Finally, strong positive vorticity advection may also (but not always) be associated with upward vertical motion, and hence, the potential for thunderstorm development.
stratocumulus lines
form when cold air is advected over warmer water , accompanied by strong low level winds ≥15 Kts and a cap (inversion) to vertical cloud development. Elements form a line of connected stratocumulus (SC) and align with the wind direction. Normally has a well-defined clear area upstream near the coastline. On visible imagery, SC lines appear light gray to white. The smaller the elements and more closely packed the SC lines, the stronger the low-level winds. As winds decrease downstream, elements become larger.
cold core barotropic low
frequently develop as a result of the occlusion of a baroclinic low pressure system. They possess the following characteristics: Vertically stacked Not directly associated with a frontal boundary Cold air throughout the atmospheric column Low thicknesses, and thus, low upper level heights Circulation strengthens with height
cold front
front represents the replacement of a warm(er) air mass with a colder airmass accompanied by the arrival of a drier airmass, and a wind shift from south or southwest to northwest. Cold fronts are situated within a trough of low pressure extending south from a low pressure center, and tend to move faster and have a steeper slope than other types of fronts. This steep slope produces strong vertical lifting, conducive for the development of deep convection, if other favorable convective parameters (instability, moisture, etc.)
storm relative helicity
in meters squared per second squared (m2/s2), is a measure of the storm relative rotation and shear in the atmosphere. SRH depends on: Speed shear: How much wind speed increases with height from 0 to 1 km or 0 to 3 km. Directional shear: How much wind direction changes with height from 0 to 1 km or 0 to 3 km. The strength of the low level wind interacting with the speed and directional shear. SRH can be used to determine if the vertical wind shear is strong enough to allow storms to become severe or supercellular. 0 to 3 km SRH greater than 250 m2/s2, and 0 to 1 km SRH greater than 100 m2/s2, suggest an enhanced threat of tornadoes.
wet bulb zero height
is the temperature a parcel of air would have if cooled adiabatically to saturation at constant pressure by evaporation of water into the parcel. The wet bulb zero height is the height at which the wet bulb temperature drops to or below 0 degrees Celsius. Wet bulb zero (WBZ) heights of 5,000 feet to 11,000 feet correlate well with severe hail in thunderstorms. WBZ heights of approximately 9,000 feet have been found to be particularly favorable for severe hail.
thickness
it is a measure of the vertical depth of a layer of the atmosphere. Thickness values can be used to determine how warm or cold a given layer is. Higher (lower) thickness values indicate that temperatures within the layer are warmer (cooler), and therefore, the depth of the layer is greater (smaller). This is because warm air is less dense than cold air.
OCDS 11
lets users generate tailored climate summary reports by individual and multiple weather parameters. Upgraded application allows: Monthly update feature that keeps the extremes constantly updated A standard period of record summary Rigorously quality controlled data Convenient output in HTML, CSV or XML Pay attention to the advisory statement at the top, indicative of how reliable the information presented is.
theta E
measure of the temperature a parcel of air would have if lifted to saturation, thus releasing the latent heat in the parcel, and then lowered dry-adiabatically to 1000mb. Theta-e takes into account both the moisture content and temperature of the air, with theta-e increasing as temperature and moisture increase. Areas of high theta-e are positively buoyant and unstable, and thus more favorable for thunderstorm development. Theta-e ridges, regions of particularly high theta-e, can be found in areas of strong warm air and moisture advection, and are prime locations for thunderstorms.
CAPE
measured in units of Joules per kilogram (J/kg), is a measure of the amount of positive buoyant energy available to an ascending parcel. On a Skew-t diagram (Fig. 1), CAPE is the positive area enclosed by the environmental temperature profile and then the profile of a lifted air parcel from the level of free convection (LFC) to the equilibrium level (EL). In other words, it is the area on the diagram where the parcel sounding is to the right of the environmental sounding. The larger the positive area on the sounding, the greater the CAPE and instability will be High CAPE values result in greater vertical motion within thunderstorms (stronger updrafts). Therefore, storms in high CAPE environments are more likely to produce severe weather such as large hail and convective winds. When determining severe thunderstorm potential, CAPE should not be used alone. In some situations with high CAPE, storms will not form due to strong convective inhibition (CIN, described below). Conversely, severe storms may occur in environments of low CAPE and strong vertical wind shear
CIN
measured in units of Joules per kilogram, is the amount of energy required to lift an air parcel from some originating level to the LFC. CIN is the area on a Skew-t, below the LFC, where the parcel sounding is to the left of the environmental sounding. The larger the area of CIN, the less likely it is that ascending parcels will reach the LFC, with values of CIN greater than 100 J/kg considered prohibitive to convective development. However, factors such as surface heating and moistening, frontal lifting, and orographic lifting can overcome CIN. If large CIN is overcome, explosive thunderstorm development is possible. Note, however, that low CIN can also be detrimental to severe weather. In a low CIN environment, convection may develop early in the day, before maximum heating and instability can be realized
Tornado climatology
most favorable juxtaposition of environmental ingredients for tornadogenesis usually develops in the mid-latitudes, between about 30°and 50°North or South. The United States experiences the most tornadoes per year, followed by Canada. However, tornadoes are also common in northern Europe, western Asia, Bangladesh, Japan, Australia, New Zealand, China, South Africa, and Argentina
stationary front
neither air mass is replacing the other. A temperature gradient still exists along a stationary front, but temperature advection is weak because the flow is parallel to the front. Stationary fronts generally possess the characteristics of a warm front, with stratiform clouds and precipitation on the cool side and possible convection on the warm side. Flooding rains are possible if multiple disturbances propagate along the front, producing repeated rounds of heavy precipitation over the same locations
numerical weather models
procedure used to forecast the weather by computer. The behavior of the atmosphere is governed by a set of physical laws that can be expressed as mathematical equations—taking into account how temperature, pressure etc. will change from their values at the present time. By using forms of the equations that have been adapted for numerical methods, we can calculate the future values of the fields. Since the equations are very complex there are no exact solutions that can give us perfect forecast values. Therefore models are used for approximatesolutions
bulk Richardson number BRN
ratio between the instability (CAPE) and vertical wind shear of the environment. If CAPE is much stronger than shear, storms are likely to be of the pulse or multi-cell variety. If shear is disproportionately strong compared to CAPE, storms may be torn apart. However, if CAPE and shear are balanced and significant, severe thunderstorms are likely.
warm front
replacement of a cold airmass with a warmer airmass. Warm fronts are also accompanied by a wind shift from the east or southeast to southwest. Warm fronts have a much gentler slope than cold fronts as the warm air overruns the cold air mass, it cools to saturation, resulting in extensive fog, stratiform cloudiness, and light precipitation in advance of the warm front. If a shallow layer of subfreezing air resides near the surface, below the overrunning warm air, freezing rain may become a significant threat. During the spring, severe thunderstorms may also occur in the vicinity of a warm front. Within a zone extending from about 10 miles on the warm side of the front to 30 miles on the cool side of the front, conditions may become particularly favorable for tornadic storms. This is because directional wind shear is enhanced along the frontal boundary
frontolysis
represented by a decrease in the strength of the temperature gradient along an existing front.
dry lines
sharp gradient between moist tropical air and dry continental air, and are typically found east of the Rocky Mountains in Kansas, Oklahoma, and Texas. It is not uncommon for dew points to fall 30 degrees or more from the east side of a dry line to the west side. Dry lines tend to oscillate back and forth, retreating westward at night, and advancing to the east during the day. Under certain circumstances, severe convection can occur along a dry line. For convection to develop, there must be convergence, which may be aided by strong upper level winds overriding the dry line and/or by the advection of warm, moist air directly toward the dry line. The convergence must be strong enough for upward vertical motion to break through an EML (elevated mixed layer) of dry, warm air aloft. If this occurs, thunderstorms, often in the form of supercells, will develop
cloud streets
similar to cloud lines, but the elements are not connected. Cumulus (CU) is generally parallel to the low-level wind flow. Often provide excellent representation of the anticyclonic flow around high pressure systems.
DCAPE
the opposite of CAPE. It is a measure of the amount of negative buoyant energy available to a saturated parcel of descending air. DCAPE can be found on a Skew-t by first identifying the level of downdraft origination aloft. This can be done by arbitrarily using a level between 700 mb and 600 mb as the origination level and finding its lifting condensation level (LCL), and then following the moist adiabat through this level to the surface. A more accurate method is to use observed or forecast Skew-t data to determine the level of minimum wet bulb potential temperature aloft, which is the typical level of approximate downdraft origination. The DCAPE is proportional to the area between the line following the moist adiabatand the temperature curve. Large values of DCAPE (generally 800 J/kg or greater) indicate an enhanced potential for downbursts, making this parameter particularly important for aviation forecasting
Climatology
the scientific study of climate
closed cell stratocumulus
typically associated with anticyclonic flow. Wind direction is difficult to determine by the clouds alone, but wind speeds are typically less than 20 knots.
frontogenisis
typically evidenced by the development of a temperature gradient, or increase in strength of an existing gradient
supercell composite parameter SPC
used to estimate the potential for elevated and surface-based supercells where the MUCAPE is the most unstable parcel CAPE. Each of the individual ingredients has been normalized by threshold values deemed to be physically significant with respect to supercell formation.
Gibson ridge 3 gr3
utilized by flight weather units for daily customer support and hosted on the forecaster's workstation. GRLevel3 Version 2 is a Windows viewer for live and archive NEXRAD Level III data. GR3 displays high resolution base products, dual-polarization products, and derived products along with Local Storm Reports (LSRs) and severe weather warnings.
warm core barotropic high
warm air throughout the atmospheric column. Other characteristics of warm core barotropic highs include: • Vertically stacked • Anticyclonic circulation strengthens with height • Not directly associated with a frontal boundary • Associated with fair weather and warm temperatures The most common type of warm core barotropic high is the subtropical high. The high is caused by air moving northward from the tropics. By around 30 degrees latitude, the northward motion slows due to the Coriolis effect, causing upper level convergence, and thus, high pressure
subtropical jet
weaker than the polar front jet caused by slight temperature gradients along the boundary of the Hadley and Ferrel cells in subtropical latitudes It is usually located at the 200 mb level, between 35° N and 25° N As a rule of thumb, it can be found by locating the strongest winds on the 200 mb chart, or the -11° C isotherm at the 500 mb level
climatic events
weather elements used to describe climate. Temperature is the most important and moisture is the second.
