Weather Flashcards
What is the standard temperature (in °F and °C) and pressure at sea level?
59°F, 15°C, 29.92” Hg.
What is every physical process of weather accompanied by, or the result of?
Heat exchange.
What causes variations in altimeter settings between weather reporting points?
Uneven heating of the earth’s surface.
What causes differences in direction between winds aloft and on the ground?
Friction between the wind and the surface.
What is a front?
The boundary between two different air masses.
What weather phenomenon will always occur when flying across a front?
A change in the wind direction.
What is one of the most easily recognized discontinuities across a front?
A change in temperature.
How many families of clouds are there? How are they classified?
- According to their height range.
What does the suffix “-nimbus” mean when naming clouds?
It means a rain cloud.
How is moisture added to unsaturated air?
By evaporation and sublimation.
What will always happen when water vapor condenses?
Clouds, fog, or dew will be formed.
If the temperature/dewpoint spread is small and decreasing, and the temperature is 62°F, what will happen?
Low clouds or fog are likely to develop.
How can you calculate the altitude of the base of cumulus clouds?
Divide the temperature/dewpoint spread by 4.4, and multiply by 1000.
How can you determine the stability of the atmosphere?
Compare the actual lapse rate with the standard lapse rate.
What is the standard lapse rate?
3.5°F per 1,000 feet.
What will moist, stable air flowing upslope produce?
Stratus clouds.
What characterizes stable air?
Stratiform clouds, steady vs. showery precipitation, smooth air (little or no turbulence), and poor surface visibility.
What does warming from below do to an air mass?
It decreases its stability, because it develops thermals.
What causes the development of thermals?
Heating from below.
What characterizes unstable air?
Turbulence and good surface visibility (because the rising air carries away pollution and haze in the lower atmosphere).
If clouds form in a moist, unstable air mass, what kind will they be?
Cumuliform clouds and showery precipitation.
What happens when an unstable air mass is forced upward?
It produces clouds with considerable vertical development and associated convective turbulence.
What indicates convective turbulence?
Towering cumulus clouds.
What is one in-flight condition necessary for structural icing to form?
Visible moisture.
When is the highest accumulation rate of aircraft structural ice most likely?
In freezing rain.
What are ice pellets at the surface evidence of?
A temperature inversion with freezing rain at a higher altitude.
What causes frost?
The temperature of the collecting surface being at or below the dewpoint of the adjacent air and the dewpoint being below freezing.
When does a temperature inversion occur? What is the result?
When the air above is warmer than the air below.
An increase in temperature as altitude is increased, and a stable layer of air.
When can you expect a wind shear zone in a temperature inversion?
When the windspeed at 2,000 to 4,000 feet above the surface is at least 25 knots.
What most frequently produces a ground or surface-based temperature inversion?
Terrestrial radiation on a clear, still night. If it’s cloudless, the heat won’t be trapped. Heat radiating off the surface cools down the ground; which cools the air next to the ground, causing radiation or ground fog to form.
Where is radiation fog most likely to develop?
In warm, moist air over low, flatland areas on clear, calm nights.
When is advection fog most likely to form?
When an air mass moves inland from the coast in winter.
What creates upslope fog?
Air cooling as it is forced to rise up a slope.
What two types of fog depend on wind in order to exist?
Advection fog and upslope fog.
Why is steam fog especially dangerous?
Low level turbulence can occur, and icing can become hazardous.
Which clouds have the greatest turbulence?
Cumulonimbus (thunderstorm) clouds.
Which hazardous atmospheric phenomenon near thunderstorms should be expected on landing approach?
Wind shear turbulence.
Which weather phenomenon is always associated with a thunderstorm?
Lightning.
What are squall line thunderstorms?
A nonfrontal, narrow band of active thunderstorms that often develop ahead of a cold front. They are very hazardous to aircraft.
What conditions are necessary for the formation of cumulonimbus clouds?
A lifting force, unstable air, and moist air.
What are the three stages of a thunderstorm?
- CUMULUS - continuous updrafts.
- MATURE - precipitation beginning to fall. Greatest intensity.
- DISSIPATING - predominantly downdrafts.
What’s an AIRMET?
A warning of weather conditions particularly hazardous to small single-engine aircraft. However, they are for all pilots.
What’s a SIGMET?
Significant. A warning of weather conditions hazardous to all aircraft.
Which reports tell you about freezing levels and moderate icing?
AIRMETs.
Which reports warn you of severe icing not associated with thunderstorms?
SIGMETs.
Where would you find information on freezing levels and areas of probable icing aloft?
Inflight Aviation Weather Advisories.
What does a convective SIGMET contain?
A warning of tornadoes, embedded thunderstorms, and hail 3/4 inch or greater in diameter.
What are embedded thunderstorms?
Thunderstorms that are obscured by massive cloud layers and cannot be seen.
Where does wind shear occur?
At all altitudes, in all directions.
Where can hazardous wind shear be expected?
In areas of low-level temperature inversion, frontal zones, and clear air turbulence.
What is a standing lenticular cloud?
A stationary, almond or lens-shaped cloud that indicates the crest of a standing wave. It may contain winds of 50 knots or more.
How can you anticipate possible mountain wave turbulence?
When winds of 40 knots or greater blow across a mountain ridge, and the air is stable.
What is ceiling?
The height above the earth’s surface of the lowest layer of clouds or obscuring phenomena reported as either broken or overcast (provided it is not called thin or partial).
What are surface observations?
METAR and SPECI weather reports.
In surface observations, or the winds true or magnetic?
True.
Decode this:
SPECI KMDW 121856Z 32005KT 1 1/2SM RA OVC007 17/16 A2980 RMK RAB35
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What are TAFs? When are they issued? How long are they usually valid for?
Terminal Aerodrome Forecasts. Issued four times a day. Generally valid for 24 hours (30 hours at airports that serve long-range aircraft).
What is the only cloud type forecast in TAFs?
Cumulonimbus.
Decode some TAFs.
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Decode some winds and temperature aloft forecasts.
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How is windspeed less than 5 knots (light and variable) encoded in a winds and temperatures aloft forecast?
9900.
Decode an area forecast.
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Decode a weather prediction chart.
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Decode a low level prognostic chart.
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What does a low level prognostic chart depict?
Areas to avoid (freezing levels and turbulence).
What is a weather depiction chart used for?
To determine general weather conditions on which to base flight planning.
What does a winds and temperatures aloft forecast show?
- Wind direction relative to true north.
- Wind speed in knots.
- Temperature in °C.
What is an aviation area forecast for?
To determine general forecast weather conditions over several states.
Decode a pilot report.
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What do radar weather reports depict?
Location of precipitation, along with type, intensity, and cell movement.
Decode a radar summary chart.
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What do radar summary charts show?
Lines and cells of hazardous thunderstorms, which are not shown on other weather charts.
How are echo tops shown on radar summary charts?
In hundreds of feet MSL, with a 3-digit number above the line.
How are precipitation intensity levels shown on radar summary charts?
By contour lines.
- Level one shows light to moderate.
- Level two shows heavy to very heavy.
- Level three shows intense to extreme.
What do arrows and feathers on a radar summary chart indicate?
Radar return direction and speed of movement.
How are severe weather watch areas depicted on a radar summary chart?
They are enclosed by heavy dashed lines forming a rectangle.
On a radar summary chart, what kind of weather are Severe Weather Watch Areas issued for?
Tornadoes and severe thunderstorms.
When you telephone a weather briefing facility for preflight weather information, what should you tell them?
- That you are a pilot.
- Tail number or pilot’s name.
- VFR or IFR.
- Intended route and destination.
- Type of aircraft.
When should you request a standard briefing?
When you want the complete weather briefing for the planned flight or, when departing within the hour, if no preliminary weather information has been received.
When should you request an abbreviated briefing?
When you want to update a previous weather briefing, or to supplement mass disseminated data.
When should you request an outlook briefing?
When information is requested 6 or more hours in advanced of the proposed departure time.
How can you obtain enroute weather advisories?
From an FSS on 122.0 MHz, below FL180.
What is EFAS?
Enroute Flight Advisory Service; also called “Flight Watch”. It provides actual weather and thunderstorm information along your route. It can be contacted by calling Flight Watch on 122.0 MHz.
What’s a TWEB?
Transcribed weather broadcast. It gives a recorded weather briefing for specific routes of flight, including winds aloft and route forecasts.
How can you monitor a TWEB?
Tune your VHF receiver to an appropriate VOR frequency, or tune your ADF receiver to an appropriate NDB frequency.
What does the absence of sky condition and visibility on an ATIS mean?
The ceiling is at least 5,000 feet, and the visibility is 5 miles or more.
What is dew point?
The temperature to which air must be cooled to become saturated.
If relative humidity is 100%, will you get clouds, fog or dew?
Not necessarily. The water can sublimate.
What is lapse rate?
The decrease of temperature with altitude.
What is unstable air?
Air that gets colder with altitude more quickly than standard.
How does steam fog form?
When arctic cold air from the land moves over the relatively warmer ocean.
What are Inflight Aviation Weather Advisories?
A collective term for AIRMETs, SIGMETs, and convective SIGMETs.
What’s the difference between a METAR and a SPECI?
A metar is a routine weather report. A SPECI is a special weather report.
In a surface observation, what does BR stand for?
Mist (think “baby rain”).
In a surface observation, how do you analyze the cloud layer heights?
Add two zeroes to the given number.
For the following SPECI, what do the remarks mean?
SPECI KMDW 121856Z 32005KT 1 1/2SM RA OVC007 17/16 A2980 RMK RAB35.
SPECI report for KMDW. Report was issued on the 12th of the month, at 18:56 ZULU. Wind is from 320 true, at 5 knots. Visibility is 1 1/2 statute miles. Rain. Overcast cloud layer at 700 feet AGL. Temperature is 17°C, dewpoint is 16°C. Altimeter setting is 29.80. The rain began at 1835 ZULU.
What is the only cloud type that is forecast in a TAF?
Cumulonimbus, as “CB”.
In a TAF, what does BECMG mean?
“Becoming” – a gradual change.
In a TAF, what does SKC mean?
Clear sky.
In a TAF, what does TEMPO mean?
Temporarily.
If your destination does not have a terminal forecast, what would you use?
An area forecast.
How large of an area does the “VFR clouds and weather” section of an area forecast cover?
Greater than 3,000 square miles.
If asked “What is the valid time for the forecast” for an area forecast, to what time are they referring?
The VFR clouds and weather forecast, not the synopsis.
What do weather depiction charts show?
Areas of IFR, marginal VFR, and VFR weather conditions.
On a weather depiction chart, what is VFR weather?
Ceilings greater than 3,000 feet, and visibility greater than 5 miles.
What can you determine from the station circles on a weather depiction chart?
The amount of shading inside each circle represents the cloud coverage. A solid circle is overcast. Add two zeroes to the accompanying number to determine the height of the clouds.
How are visibilities shown on a weather depiction chart?
The are given to the left of the station circle, unless they are greater than 5 miles.
On a weather depiction chart, what do two dashes between the visibility distance and the station circle mean?
That the restriction to visibility is fog.
On a weather depiction chart, what do two solid circles mean, between the visibility distance and the station circle?
That the restriction to visibility is rain.
On a weather depiction chart, what does a solid circle with a triangle under it mean, between the visibility distance and the station circle?
That the restriction to visibility is rain showers.
On a weather depiction chart, what is a front with triangular symbols?
Cold front. It’s moving in the direction that the triangles are pointing.
On a weather depiction chart, what is a front with half-circles?
Warm front.
On a weather depiction chart, what is a front with triangles on one side, and half-circles on the other?
A stationary front.
What are low-level prognostic charts for?
They are forecast charts.
The top two are significant weather forecast charts; they show forecast areas of IFR and marginal VFR weather, plus turbulence and freezing levels.
The bottom two are surface prognostic charts; they show forecast positions of pressure systems plus fronts and precipitation.
The two left-hand charts are 12-hour forecasts, and the two right-hand charts are 24-hour forecasts.
How is turbulence shown on a significant weather forecast chart?
The symbol for moderate turbulence is a little mountain peak. If it has an inverted V on it, it means severe turbulence.
Under the turbulence symbol is a number indicating the top of the turbulence. Add two zeroes to it. Then, a slash, and the bottom altitude of the turbulence. If no number, then the turbulence goes down to the surface.
How do you find the freezing level on a significant weather forecast chart?
Add two zeroes to the number accompanying the freezing level lines.
Decode these weather symbols: http://upload.wikimedia.org/wikipedia/en/1/1f/Weather_symbolsNEW2.png .
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In a PIREP, are the cloud bases and tops in MSL or AGL?
MSL.
What do radar summary charts show that other charts do not?
Lines and cells of hazardous thunderstorms.
On a radar summary chart, what does a heavy dashed line forming a rectangular box mean?
Severe weather watch area.
How do you know when a TWEB is available?
On a chart, look for a white T in a circle, inside an identification box.
What’s HIWAS?
Hazardous In-Flight Weather Advisory Service.
Continuous broadcast of hazardous weather information: developing thunderstorms, turbulence, and IFR conditions.
How do you know which stations have HIWAS?
An “H” in a circle in an NAVAID box, in the upper right-hand corner.
