Weather Information Flashcards
METAR
Meteorological Terminal Aviation Routine Report
- Surface Aviation weather observation
- Updated every hour
- Current conditions based on ATIS, AWOS and ASOS
- SPECI: special report to update current METAR for rapidly changing weather conditions
- Location, time, wind direction (magnetic), wind speed (knots), visibility (statute miles), cloud cover, cloud height, temp, dew point, altimeter, remarks
METAR KSTS 261451Z 30008KT 10SM SCT120 26/22 A3012
TAF
Terminal Aerodrome Forecast
- Forecast - Valid 24 hrs - Updated 4 times/day, within 5nm of airport
- Location, time issued, valid time, wind direction, wind speed, visibility, cloud cover, cloud height, potential severe weather
TAF KSTS 261121Z 261212 VRB03KT P6SM BKN200
BECMG 1314 22005KT FEW025
FA (Area Forecast)
- Forecast of VFR clouds and weather conditions
- Size of several states (~3000 sq miles)
- Broken up into 6 different regions -updated 3x a day
- 24 hr period ( 18 hr forecast, 6 hr categorical outlook)
- Cloud height, cloud cover, visibility, expected precipitation type and intensity
The area forecast together with the AIRMET Sierra bulletin are used to determine forecast en-route weather and to interpolate conditions at airports which do not have a terminal forecast (TAF) issued.
- Consists of:
- 12 hour forecast plus a 6 hr categorical outlook. All times are Coordinated Universal Time (UTC). All distances except visibility are in nautical miles. Visibility is in statute miles.
Synopsis section which is a brief summary of the location and movement of fronts, pressure system, and circulation patterns for an 18 hour period.
VFR clouds and weather section which is a 12 hour forecast, in broad terms, of clouds and weather significant to flight operations plus a 6 hour categorical outlook. This section is usually several paragraphs. AIRMET Sierra supplies information regarding Instrument Flight Rule (IFR) conditions. The breakdown may be by states, by well-known geographical areas, or in reference to
location and movement of a pressure system or front. A categorical outlook, identified by OTLK, is included for each area breakdown
PIREP
Pilot Weather Report
- UA: Routine PIREP
- UUA: Urgent PIREP
- Confirm conditions, ceiling, visibility, precipitation, icing, turbulence
ATIS
Automated Terminal Information Service
- Updated after receipt of weather observation
- Use Below 3000’ AGL
- Contains: Wind, Vis, Sky Condition, Temp/Dew, Altimeter, Remarks: Landing Runway and What Approach is in Use. (runways in use, runway/taxi way closures, ect.)
ASOS
Automated Surface Observation Service
- Continually updates
- Wind direction, speed, temp, dew point, pressure, cloud type, type of precipitation
AWOS
Automated Weather Observation Service
- Continually updated
- AWOS 1 - Wind, Vis and Altimeter
- AWOS 2 - 1 and Sky Condition and Temp/Dew
- AWOS 3 - 1 and 2 plus Density Alt.
ASOS
Automated Surface Observation System
- Better than AWOS
- Gives you everything
- Wind, Vis, Sky, Temp/Dew, Altimeter, cloud type, precipitation and Runway Information
Radar Summary Chart
- Based on precipitation (Echo return)
- Observed areas of precipitation, intensity, heights of tops of echoes, types of precipitation, sever weather watches
- Updated hourly
Lt. Green - Weak Precip, no turbulence
Yellow - moderate precip and moderate turb
Red - Heavy Precip & Severe Turbulence
Surface Analysis Chart
- METAR Reports shown over continental US
- Updated every 3 hours
- Shows Fronts, Pressure Systems and Isobars
- For planning flights, based on the fronts and winds/Temps
- Trough is an elongated low pressure
- Ridge is an elongated high pressure
The surface analysis chart is a computer-generated chart, with frontal analysis by
Forecasters, transmitted every 3 hours covering the contiguous 48 states and adjacent areas.
Weather Depiction Chart
- Shows where it’s IFR, MVFR and VFR
- METAR Reports shown over continental US
- Consists of fronts, high/low pressure, cloud cover, visibility (doesn’t show pressure millibars like Surface Analysis Chart)
- IFR/VFR/MVFR areas
- updated ever 3 hours
Weather Ceiling/Visibility Categories
VFR- ceiling >3000AGL, visibility >5 sm
MVFR- ceiling 1000-3000AGL, visibility 3-5 sm
IFR- ceiling 500-1000AGL, visibility 1-3 sm
LIFR - ceiling <500AGL, visibility <1 sm
Significant Weather Prognostic Charts (SIGWX)
A four-panel chart that includes 12– and 24–hour forecasts for significant weather and surface weather. The valid time for the chart is printed on the lower left corner.
The upper two panels show forecast significant weather, which may include non-convective turbulence, freezing levels, and IFR or MVFR weather.
The lower two panels show the forecast surface weather and depicts the forecast locations and characteristics of pressure systems, fronts, and precipitation.
- Used to review flight conditions for flight planning/briefing
- Low level is Surface to FL240
- Mid level is FL100 to FL450
- High level FL250 to FL630
- 12 & 24 hr forecasts for areas of VFR, MVF, IFR, turbulence, freezing levels
- Updated every 6 hours (4x daily)
AIRMET (Airmen’s Meteorological Information) (WA)
Focus on weather that may adversely affect aircraft safety in still flyable weather
-Forecast for hazardous weather for light aircraft
-Issued every 6 hours
Sierra: IFR and mountain obscuration
Tango: moderate turbulence, strong surface winds (over 30kts), low level wind shear
Zulu: icing and freezing levels
SIGMET (Significant Meteorological Information) (WS)
- Non-convective hazardous forecasts for all aircraft
- Conditions: Moderate to Severe
- Issued as required valid for 4 hours
- Cover area of 3,000 miles
- severe icing not associated with T-Storms
- severe turbulence or CAT not associated with T-Storms
- sandstorms/dust storms that lower vis. <3sm
- volcanic ash
- Types November through Yankee
Convective SIGMET (WST)
- Issued as required
- Valid for 2 hours
-Moderate to severe thunderstorms covering 40% of
the area - Surface Winds > 50 kts
- Thunderstorm lines at least 60 miles long
- Embedded thunderstorms -Tornadoes
- Hail over 3/4’’
- Severe Icing Conditions
G AIRMET
Graphical AIRMET
Radar Summary
- Observed areas of precipitation, intensity, heights of tops of echoes, types of precipitation, sever weather watches
- Updated hourly
Winds and Temperatures Aloft
- Forecast based on upper air observations from a weather balloon
- Determine winds for flight planning
- Location, altitude, wind direction (true north)/(temp c)
- updated 4 times a day
- 9900 Light and variable less than 5 kts -0000KT calm
- no winds given 1500 AGL, use METAR
- no temps given if stations is within 2500 AGL
- Temp inversions, best cruise altitude
Flight Service Station (FSS)
-primary source for preflight weather information
1-800-WXBRIEF
HIWAS
Hazardous Inflight Weather Advisory Service
-AIRMETs, SIGMETs, Convective SIGMETs, Urgent PIREPS
Weather Briefings
- Standard: most complete briefing
- Abbreviated: shortened version of standard, used to update previous briefing
- Outlook: forecast information 6 or more hours away
Composition of the Atmosphere
78% Nitrogen
21% Oxygen
1% Trace gases (argon, CO2, etc)
0-5% water vapor, this amount of water vapor is responsible for major changes in weather
Layers of the Atmosphere (Lowest to Highest)
-Troposphere (Tropopause-boundary layer that traps moisture and associated weather in the troposphere) -Stratosphere -Mesosphere -Thermosphere
Atmosphere Circulation
- Atmosphere is always in motion trying to find its equilibrium
- Major factor in atmospheric circulation is the uneven heating of Earth’s surface
Standard Atmospheric Properties
Sea Level Pressure and Temperature
-29.92”Hg (1,013.25millibars) and 15°C
Pressure change with altitude
1” Hg per 1000 ft
Characteristics associated with Low Pressure System
Air circulation is inward, upward, and counterclockwise.
-Area or rising air, which is conductive to cloudiness, precipitation, and bad weather
Characteristics associated with High Pressure System
Air circulation is outward, downward, and clockwise
-Area of descending air which tends to favor dissipating clouds and good weather
Unstable Air
Warm moist air
Stable Air
Cool dry air that resists vertical movement
Standard Lapse Rate
2°C per 1,000’
Isobar
line on a weather chart which connects areas of equal or constant barometric pressure.
Ridge
- Elongated area of high pressure
- High pressure ridge is depicted as yellow zig zag lines on a surface analysis chart
Trough
- Elongated Area of low pressure
- Low pressure trough is depicted as an orange dashed line on a surface analysis chart
Temperature Inversion
- When the temperature of the air rises with altitude
- smooth stable air, but usually poorer visibility if realative humidity is high
Relative Humidity
Actual amount of moisture in the air compared to the total amount of moisture the air could hold at the temp.
Dew Point
Temperature at which the air becomes saturated and the air condenses into fog, dew, frost, clouds, rain, or snow.
Dew point is the temperature to which a sample of air must be cooled to attain a state of saturation.
Sublimation
Solid to Gas. The water absorbs heat from surroundings
Deposition
Gas to Solid. (Snowflakes). Water releases heat to surroundings
Evaporation
Liquid to Gas. The water absorbs heat from surroundings.
Condensation
Gas to Liquid. The water releases heat to surroundings.
Radiation Fog
Occurs on cool calm nights when surface cools and brings cooling temperatures to dew point
Advection Fog
- When warm moist air moves over a cooler surface.
- Usually in coastal areas
- Requires wind
- Golden Gate Bridge in SF good example
Upslope Fog
- When moist stable air is forced up sloping land features like a mountain
- Requires wind
Steam Fog
Dry, cool air moving over warm body of water
Ice Fog
Occurs in cold weather when temp is much below freezing and water forms directly into ice crystals
Cloud classification
Clouds are classified based on Height:
- Low: Surface-6,500 AGL
- Middle: 6,500-20,000 AGL
- High: 20,000 and above (usually stable air)
- Vertical development: Cumulus clouds (unstable)
Air Mass
Large bodies of air that take on the characteristics of the surrounding area
-Unstable Air mass: an air mass passing over a warmer surface causing convective currents of rising unstable air
Sources of Lifting
- frontal
- convective
- low pressure
- orographic
Front
Boundary layer between two types ofair masses
Warm Front
- Occurs when a warm air mass advances and replaces a body of colder air
- Gernerally stable air with poor visibility
- Slower moving front 10-25mph
Cold Front
- Occurs when a mass of cold, dense stable air advances and replaces a body of warmer air
- Cold dense air lifts the warm air up (stability of the front is dependent on the stability of the forced up warmer air mass)
- Bad Weather usually associated
- Faster moving 25-30mph or higher
Occluded Front
Occurs when a fast moving cold front catches up with a slow moving warm front.
As the occluded front approaches, warm front weather prevails but it is immediately followed by cold front weather.
Two types: Cold Front Occlusion & Warm Front Occlusion
Cold Front Occlusion
When a fast moving cold front is colder than the air ahead of the slow moving warm front
When this occurs, the cold air replaces the cool air and forces the warm front aloft into the atmosphere.
Typically, the cold front occlusion creates a mixture of weather found in both warm and cold fronts, providing the air is relatively stable.
Warm Front Occlusion
When the air ahead of the warm front is cooler than the overtaking air of the cold front behind.
When this is the case, the cold front rides up and over the warm front. If the air forced aloft by the warm front occlusion is unstable, the weather is more severe than the weather found in a cold front occlusion - t-storms, rain and fog are likely to occur
(embedded thunderstorms if cold air being forced upward is unstable)
Thunderstorm Needs
- Lifting action
- Moisture
- Unstable air
3 Stages of a Thunderstorm
1) Cumulus (updrafts, towering cumulus formation)
2) Mature - Greatest Intensity (downdrafts, shear, precipitation)
3) Dissipating (downdrafts, anvil shape)
Squall Line
- Narrow band of active thunderstorms
- Single most intense weather hazard to aircraft
Microburst
Small scale intense downdrafts, 6,000fpm that can last up to 15min
Wind Shear
Sudden or drastic change in wind speed/direction
Mountain Wave Turbulence
Wind speed at least 20 knots and perpendicular to the range
Types of Icing
Rime
Clear
Mixed
Rime Icing
- Milky in color
- Typically forms in stratiform clouds
- Builds upwards, doesn’t really flow across the wing
Clear Icing
- Clear/transparent, hard to detect
- Supercooled water typically in cumulous clouds
- Flows over the back of the wing and keeps building up
Frost
- Forms under the same conditions that are favorable for dew
- Dewpoint is less than 0 degrees Celsius (frost point)
- Surface temperature is less than dewpoint
Types of Icing
- Induction
- Airframe
- Instrument
High Pressure System
Characteristics:
- Stable Air
- Stratiform Clouds & Fog
- Steady Precipitation
- Smooth Air
- Fair to Poor Visibility
- Haze and Smoke
- Rime Icing Probability
- Typical Warm Front
A high pressure system has higher pressure at its center than the areas around it. Winds blow away from high pressure. Swirling in the opposite direction from a low pressure system, the winds of a high pressure system rotate clockwise north of the equator and counterclockwise south of the equator. This is called anticyclonic flow. Air from higher in the atmosphere sinks down to fill the space left as air is blown outward.
Low Pressure System
Characteristics:
- Unstable Air
- Cumuliform Clouds
- Showery Precipitation
- Rough Air (Turbulence)
- Good Visibility
- Blowing Obstructions
- Clear Icing Probability
- Typical Cold Front
A low pressure system has lower pressure at its center than the areas around it. Winds blow towards the low pressure, and the air rises in the atmosphere where they meet. As the air rises, the water vapor within it condenses, forming clouds and often precipitation. Because of Earth’s spin and the Coriolis Effect, winds of a low pressure system swirl counterclockwise north of the equator and clockwise south of the equator.
What does the separation of the isobars on a weather map mean?
When isobars are close together the change in pressure is steeper, likewise the further apart they are the shallower the change is.
What causes the winds aloft to flow parallel to the isobars?
the Coriolis force
When temperature and dew point are close together (within 5 degrees), what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog.
What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere.
How do you determine the stability of the atmosphere?
Unstable air - temperature decreases uniformly and rapidly as you climb. Likely to be around moist warm air.
Stable air - temperature remains unchanged or decreases only slightly.
List the effects of stable and unstable air on clouds, turbulence, precipitation, and visibility.
Stable
- Clouds: Stratiform
- Turbulence: Smooth
- Precipitation: Steady
- Visibility: Fair to Poor
Unstable
- Clouds: Cumuliform
- Turbulence: Rough
- Precipitation: Showery
- Visibility: Good
What type of wx info should you be aware of with respect to icing?
a. Location of fronts - type, speed, direction
b. Cloud Layers - bases and tops, PIREP’s
c. Freezing level(s)
d. Air Temp and Pressure - low pressure temps at and around freezing are bad
How can a pilot determine the freezing level?
Current Icing Product, Forecast Icing Products, freezing level graphics.
What conditions are necessary for structural icing?
Visible moisture and below freezing temperatures at the point the moisture strikes the a/c.
Name the main types of icing an a/c may encounter in-flight?
Structural, induction systems, and instruments icing.
Name the three types of structural icing that may occur.
Clear Ice - forms after initial impact when the remaining liquid portions of the drop flows out over the a/c surface, gradually freezing as a smooth sheet of solid ice.
Rime Ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid freezes before it can spread out.
Mixed Ice - Forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough surface
What action is recommended if you inadvertently encounter icing conditions?
Climb or descend to warmer air or dryer air.
Is frost considered to be hazardous to flight?
Yes, because frost does not change the aerodynamics of the wing but it creates air separation from the surface spoiling lift.
What factors must be present for a thunderstorm to form?
a. sufficient water vapor
b. unstable lapse rate
c. initial upward boost (lifting) to start the storm process in motion
What are the three stages of a thunderstorm?
Cumulus Stage - updrafts cause raindrops to increase in size
Mature Stage - rain at earth’s surface; it falls through or immediately beside the updrafts; lightning; perhaps roll clouds
Dissipating stage - Downdrafts and rain begin to dissipate
State two basic ways that fog may form.
a. Cooling air to the dew point.
b. Adding moisture to the air near the ground.
Name the types of fog.
a. Radiation Fog
b. Advection Fog
c. Upslope Fog
d. Precipitation-induced fog
e. Ice Fog
What causes radiation fog to form?
The ground cools the adjacent air to the dew point on calm, clear night.
What causes advection fog?
Results from the transport of warm humid air over a cold surface. Most likely to form over coastal areas during the winter.
What is upslope fog?
Forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissipates. Upslope for is often quite dense and extends to high altitudes.
Where is wind shear likely to occur?
low level temp inversion, frontal zone or thunderstorm, clear air turbulence associated with jet stream
What types of weather info will you examine to determine if wish shear might affect your flight?
Terminal forecasts (LLWS), METAR’s, SIGMET’s, conv SIGMETS, LLWAS, PIREP’s
What is the primary means of obtaining a weather briefing?
AFSS/FSS 1-800 WX BRIEF
Where can you find a listing of AFSS/FSS and weather info numbers?
Airport/Facility Directory, US govt. section of the local phone directory
What types of wx briefings are available from an AFSS/FSS briefer?
a. standard briefing
b. abbreviated briefing
c. outlook briefing
d. inflight briefing
What pertinent information should a weather briefing include?
a. adverse conditions
b. VFR flight not recommended
c. synopsis
d. current conditions
e. enroute forecast
f. destination forecast
g. winds aloft
h. notices to airmen (NOTAM’s)
i. ATC delay
j. Special use airspace
What is EFAS?
En Route Flight Advisory Service
available from 5,000 AGL to 17,500 MSL on 122.0 MHz. Known as “flight watch”
Describe several types of weather observing programs available.
Manual Observations - report made from airport staffed with FAA or NWS personnel.
AWOS - Automated weather observation system
ASOS/AWSS - Automated Surface Observation System/Automated Weather Sensor System. 25 NM range max of 10,000 ft. AGL
What are Radar Weather Reports (SD)?
Contains information about precipitation observed by weather radar. Textual product derived from the WSR-88D NEXRAD radar without human interaction. Shows coverage, precipitation, intensity, location, maximum tops, cell movement, and remarks.
What are Terminal Aerodrome Forecasts (TAFs)?
a concise statement of the expected meteorological conditions significant to aviation for a specified time period within 5 SM of the center of the airport’s runway complex.
- Valid 24 hrs
- Updated 4x daily
Define “aviation area forecast”?
FA, the is a forecast of specified weather phenomena covering a flight info region. Issued 3 times daily for all 6 regions of the contiguous 48 states.
What information is provided by an FA?
Aviation Area Forecast
Surface to 48,000 ft MSL includes:
a. synopsis - 18 hour valid period
b. clouds and weather - 12 hour period, amount (SCT, BRK, OVC) with bases higher than 1,000 ft AGL and below FL180, precipitation, visibility between 2 and 6 SM, sustained surface wind 20 kts or greater
c. 12 to 18 hour categorical outlook
What are Inflight Aviation Weather Advisories (WST,WS, WA)?
en route advisories of potentially hazardous weather in 3 types: SIGMET, convective SIGMET, and AIRMET.
What is a SIGMET (WS)?
non convective weather that is potentially hazardous to all aircraft. Maximum forecast period is 4 hours.
a. severe icing
b. severe or extreme turbulence or clear turbulence not associated with TS.
c. Dust/Sand Storms lowering vis to 3 SM or less
d. Volcanic Ash
What is an AIRMET (WA)?
(Airmen’s Meteorological Information) (WA)
Advisories of significant weather phenomena that describes conditions at intensities lower than those which require the issuance of SIGMET’s. Text (WA), graphic (G-AIRMET).
Issued on a 6 hours beginning at 0245z.
Describes the wind and temperature aloft forecast (FB).
Wind and temperature aloft forecasts are computer prepared forecasts of wind directions, speed, and temp for specified locations, altitudes, and times. Produced 4 times daily. Not forecasted below 1,500 ft.,
What valuable information can be determined from Winds and Temperatures Aloft Forecasts (FB)?
Most favorable altitude, areas of possibles icing, temperature inversions, turbulence.
What information does a weather depiction chart provide?
Weather depiction chart is computer-generated from METAR reports. Begins at 01Z each day transmitted in 3 hour intervals.
Define the terms: LIFR, IFR, MVFR and VFR.
LIFR - Low IFR, ceiling less that 500 ft and/or visibility less than 1 mile.
IFR - Ceiling 500 to less than 1,000 ft and/or visibility 1 to less than 3 miles.
MVFR - Marginal VFR, ceiling 1,000 ft to 3,000 ft and/or visibility 3 to 5 miles inclusive.
VFR - Ceiling greater than 3,000 ft. and visibility greater than 5 miles, includes sky clear.
