Weather Flashcards
What are the 3 types of of weather products?
Observation, forecast, and analysis
How frequently is a radar image/observation generated, and what is its valid time?
Generated every 4 to 11 minutes upon completion of the radar scan. The valid time is the end of the last radar scan, which is listed on the observation.
How often is the Wind and Temperature Aloft Forecast issued, and when is it valid?
4 times daily. Valid time is specified in the header, however, the information can be used during the “for use” time.
Are the winds in Winds Aloft charts true of magnetic?
True
Winds aloft chart: What does 9900 mean?
Light and Variable
When are winds and temps omitted from Winds aloft charts?
Wind is not listed within 1500ft AGL. Temps are only provided for 6,000 up MSL.
What are the issuance and valid times for the Surface Analysis Chart?
Chart is issued every 3 hours, once analysis of the observed weather is complete. Valid times are either 00, 03, 06, 09, 12, 15, 18, or 21 UTC
What type of chart is a Low Level Significant Weather Prognostic Chart?
Forecast
What are the issuance and valid times for a Low Level Significant Weather Chart?
Issued 4 times daily, valid at the specific times listed on the charts.
What type of chart is a Convective Outlook?
Forecast
What are the issuance and valid times for a Convective Outlook?
Day 1 outlook is issued 5 times daily, with the valid time specified on the chart.
What weather information does the Convective Outlook chart provide?
1) The probability of severe convection (tornados, wind gusts 50kts or greater, or hail 1 inch in diameter)
2) Non-severe convection
When is a METAR issued?
Issued hourly, usually toward the end of the hour.
What does METAR stand for?
Aviation Routine Weather Report
Are winds in a METAR true or magnetic?
True
What types of METAR stations are there, and what does each type measure?
Ao1: Station does not have a precipitation discriminator
Ao2: Station has a precipitation discriminator
What is a TAF?
Terminal Aerodrome Forecast
When is a TAF issued and what is its’ valid time?
Issued 4 times/day (000Z, 0600, 1200, 1800z), valid for either 24 hours or 30 hours, as depicted on TAF.
What is the range of a TAF?
5SM from the center of the runway complex.
What are the 4 types of inflight aviation weather advisories?
SIGMET, Convective SIGMET, AIRMET, and Center Weather Advisory
What is a Severe Weather Watch Bulletin (WW)?
WWs supplement those 4 inflight aviation weather advisories.
What is an AIRMET?
Forecast that describes significant weather occurring at intensities lower than weather requiring a SIGMET.
What does AIRMET stand for?
Airmen’s Meteorological Information
What are the issuances and valid times for AIRMETS?
Issued every 6 hours, valid for 6 hours.
What are the 3 types of AIRMETs?
Tango: moderate turbulence, sustained surface wind greater than 30kt, and/or non-convective low-level windshear below 2000ft
Sierra: extensive IFR conditions and/or mountain obscuration
Zulu: moderate icing with freezing level heights
What does SIGMET stand for?
Significant Meteorological Information
What are the issuance and valid times for a SIGMET?
Issued as necessary, valid for up to 4 hours, updated as necessary
What type of weather is included in a SIGMET?
1) Severe or extreme turbulence or clear air turbulence not associated with thunderstorms
2) Severe Icing
3) Widespread dust storm or sandstorm reducing visibility below 3sm.
4) Volcanic Ash
What is a Convective SIGMET?
Alerts pilots to more extreme weather associated with thunderstorms.
What are the issuance and valid times for a Convective SIGMET?
Issued hourly 55 minutes past the hour, updated as required. Valid for up to 2 hours
What type of weather is included in a Convective SIGMET?
1) Severe Thunderstorms due to:
-Surface Winds >= 50kts
-Hail at surface >= 3/4inch diamter
-Tornadoes
2) Embedded Thunderstorms
3) Line of thunderstorms
4) Thunderstorms producing precip greater than or equal to heavy precip affecting 40 percent or more of an area at least 3000 square miles.
What is a Center Weather Advisory (CWA)?
Unscheduled inflight weather advisory issued for hazardous weather when there is either no existing advisory, or to supplement an existing advisory.
How long is a Center Weather Advisory valid for?
2 hours
What is atmospheric stability?
The atmosphere’s ability to resist vertical movement of air
What two things determine the stability of the atmosphere?
Temperature and Moisture
What is the average adiabatic lapse rate?
2 degrees Celsius per 1000ft of altitude gain
What is the dry adiabatic lapse rate?
About 3 degrees Celsius per 1000ft altitude gain
What is the difference between wind and convective currents?
Wind moves horizontally, convective currents move vertically.
What direction do High pressure systems rotate?
Clockwise
What direction do low pressure systems rotate?
Counter-Clockwise
What is the dew point?
The temperature to which the air must be cooled to become fully saturated.
What is relative humidity?
The amount of moisture in the air compared to the total amount of moisture the air could hold at that temperature.
How does precipitation form?
It forms when water or ice particles in clouds grow to a sufficient size such that the atmosphere can no longer support them
What three ingredients are necessary for the formation of precipitation?
Water vapor, sufficient lift to condense the water vapor into clouds, and a growth process that allows cloud droplets to grow large enough to fall as precip.
What is a front?
The boundary layer between two types of air masses.
When does a cold front occur?
When a mass of cold, dense and stable air advances and replaces a body of warmer air.
Describe the typical dimensions/shape and speed of a cold front
Cold fronts move rapidly, progressing at a rate of 25-30 mph. Shaped like a snow plow, sliding under the warmer, less dense air and forcing it aloft.
What kind of weather would you expect to accompany a passing cold front?
-Sudden weather change
-Towering Cumulus or cumulonimbus clouds
-heavy showery precip
-unstable air
-lightning, thunder, hail, poor visibility, winds variable and gusty, temp and dew point drop rapidly, pressure bottoms out and begins to rise.
What type of weather do you expect after a cold front passage?
Weather clears rapidly, with good visibility and drier air prevailing. Colder temps and rising pressure also present.
When does a Warm front occur?
When a warm mass of air replaces a body of colder air.
What type of weather do you expect during a warm front passage?
Warmer temps, low ceilings, low visibilities with fog, stratiform clouds, steady continuous precipitation. If air is unstable, thunderstorms and convection can occur.
What type of weather do you expect after a warm front passage?
Steady precip and low vis with stratiform clouds tend to linger for days after passage.
What kind of weather would you expect from a stationary front?
Mixture of weather found in warm and cold fronts
What is an occluded front?
Fast-moving cold front catches up to a slow-moving warm front, forcing the warm air aloft.
What kind of weather would you expect to accompany an occluded front?
Mixture of weather found in warm and cold fronts: usually as the occluded front approaches, expect warm front weather, immediately followed by cold front weather
Describe a warm vs. cold front occlusion.
A cold front occlusion occurs when the fast moving cold front is colder than the air ahead of the slow moving warm front.
A warm front occlusion occurs when the cold front’s air is warmer than the air ahead of the warm front.
Which generally produces worse weather, a warm or cold occluded front?
Weather is more likely to be severe and convective during a warm front occlusion if the warm air being forced aloft is unstable.
What ingredients are necessary for a thunderstorm to form?
Sufficient water vapor, an unstable lapse rate, and an initial lifting action
What is “unstable” air?
Air that, when pushed upward, continues rising.
What are the 3 stages of a thunderstorm?
Cumulus: strong updrafts push warm, moist air upward until all the moisture becomes too heavy for the clouds to support
Mature: When the precipitation becomes too heavy for the updrafts to support and begins to fall. This creates strong, cool downdrafts alongside the warm updrafts
Dissipating: characterized mostly by downdrafts, which replace the updrafts, cutting off the supply of moisture. Precipitation tapers off and ends
During what stage do weather hazards generally reach peak intensity during a thunderstorm?
End of the mature stage
How long is the typical life of a thunderstorm?
Around 30 minutes
By how many miles are you supposed to circumvent a thunderstorm?
20 miles, to avoid hail and high winds
What kind of weather conditions need to exist for structural icing to form?
Temperatures around freezing and visible moisture
What is clear ice?
Transparent, smooth ice that forms when the temperature is just below freezing, allowing supercooled drops to spread out along the surface before freezing.
What is rime ice?
Rough, milky, opaque, beady ice formed by the rapid freezing of supercooled drops after the strike the aircraft.
What is mixed ice?
Combination of clear and rime icing features.
What temperature does clear, mixed, and rime ice form?
Clear: +2 to -10 C
Mixed: -10 to -15 C
Rime: -15 to -20 C
What is radiation fog?
Forms on clear nights with little to no wind when the ground cools rapidly due to terrestrial radiation causing the surrounding air temp to cool to it’s dew point.
What is advection fog?
Common in coastal areas with sea breezes, it occurs when the wind pushes a layer of warm, moist ocean air over a cold terrestrial surface which cools the moist air to the dew point.
What is upslope fog?
Occurs when wind forces moist, stable air up sloping land features like a mountain range until the moist air cools to the dew point.
What is steam fog?
Cold dry air moves over warm water - as the water evaporates is rises and resembles smoke.
What is ice fog?
Like radiation fog, except involving extremely cold, arctic temperatures that cause the water vapor in the air to form directly into ice crystals.
