Weather Flashcards
What are the standard temperature and pressure values for sea level?
- 15C or 59F
– 29.92” Hg or 1013.2 mb
Discuss isobars. What does it mean when the isobars are close together?
Isobars connect equal lines of pressure.
Closely spaced isobars means that there is a strong pressure gradient and winds will be strong.
How do surface winds flow in relationship to isobars? Why? Winds aloft?
At the surface, winds flow at an angle to the isobars because of surface friction.
Aloft, winds from more or less parallel because of the Coriolis force.
What type of clouds, visibility and precipitation would you expect from stable air?
stratiform clouds, poor visibility, smooth air, steady or continuous precipitation
What type of clouds, visibility and precipitation would you expect from Unstable air?
Cumuliform clouds or clouds with vertical development, good visibility, turbulence, and showery precipitation
What are the general characteristics of low/high pressure areas?
Low – Cyclone – counterclockwise and rising air
High – Anti Cyclone – clockwise and descending air
What is a ridge? Trough?
Ridge – extended area of high pressure – descending air
Trough – extended area of low pressure – rising air
What must be present in order for a thunderstorm to form?
- Unstable Atmosphere
- Lifting Action
- Sufficient Moisture
What are the stages of a thunderstorm?
- Cumulus (Updrafts)
- Mature (Updrafts + Downdrafts)
- Dissipating (Downdrafts)
What is wind shear? Why is it an operational hazard?
Rapid change in wind direction or velocity
It can cause dramatic changes in indicated airspeed and causes severe turbulence within the shear zone
What is wind shear? Why is it an operational hazard?
Rapid change in wind direction or velocity
It can cause dramatic changes in indicated airspeed and causes severe turbulence within the shear zone
What does dew point mean?
The temperature at which the air becomes saturated
Discuss the types of fog. Advection, Radiation, Upslope, Precipitation-Induced
Advection: moist warm air moves over colder land or water
Radiation: forms on clear nights with little or no wind and only over land
Upslope: moist unstable air is cooled as wind pushes it up a slope
Precipitation Induced: warm rain falls through cool air. Evaporation from the rain
saturates the cool air and fog forms.
What is induction icing?
This includes any icing that impedes that process of air entering the intake manifold to be mixed with fuel. Ice that builds up on the air intakes is an obvious form of this.
Carburetor ice is also a form of induction icing.
This can be attributed to the incomplete vaporization of fuel in combination with the pressure decrease inside of the
venturi. Even on a day as warm as 70°F, carburetor ice can began to form with adequate moisture in the air.
What is Instrument Icing?
Icing of the pitot tube or static ports can cause the instruments to give inaccurate readings or to fail completely.
What is Structural Icing?
Ice that forms on the surface of the aircraft. Since airfoils create lift by decreasing the pressure and thus the temperature of the air around them, icing on the propeller, horizontal and vertical tail surfaces, and wings can form at ambient
temperatures that are above the freezing level.
What is Rime Ice?
Small rain drops found in stratified clouds or drizzle freeze upon impact with the airfoil. Air that is trapped between the droplets give the ice a white or opaque appearance. It builds up typically at the leading edge only and has an irregular shape.
This makes it more easily recognizable to the pilot and easier to remove by deicing equipment.
What is Clear Ice?
Large super-cooled water droplets found in either heavy rain or in cumuliform clouds strike the airfoil but do not freeze immediately. Instead they slide backwards across the surface as they freeze. Clear ice is smooth and glossy making it very difficult to see from the cockpit. Because it adheres to the surface beyond the leading edge it can be difficult to remove.
What is mixed ice?
Occurs when drops vary in size.
What types of weather briefings can you get from a Flight Service Station briefer?
Standard – Should be requested when planning a flight and no previous weather information has been gathered
Abbreviated – Used to supplement mass disseminated data or to update a previous briefing
Outlook – Request when proposed departure time is 6 or more hours away.
What is a METAR? Types, issue, and valid times?
Aviation Routine Weather Report
Routine or special
Issued hourly
Valid for the hour
What is a TAF? Issue, valid times, area of coverage?
Terminal Aerodrome Forecast
Issued 4 times a day (every 6 hours)
Valid for 24-30 hours
Forecast for area within 5sm of airport
What is the definition of a ceiling?
The height above the ground of a broken or overcast layer
Does a TAF report cloud ceilings in MSL or AGL?
MSL
Describe FROM, BECMG, TEMPO, PROB, on a TAF?
FROM – Rapid change occurring within 1 hour
BECMG – Gradual change to take place over the course of 1 hour
TEMPO – Between the predicted period, this weather will only occur for less than an
hour
PROB – number placed afterwards is the probability of the weather forecasted to occur
Describe FROM, BECMG, TEMPO, PROB, on a TAF?
FROM – Rapid change occurring within 1 hour
BECMG – Gradual change to take place over the course of 1 hour
TEMPO – Between the predicted period, this weather will only occur for less than an
hour
PROB – number placed afterwards is the probability of the weather forecasted to occur
AIRMET? Issue, valid times, Sierra, Tango, Zulu?
Airmen’s Meteorological Information
Issued for: Mountain obscuration and widespread IFR conditions (Sierra)
Moderate turbulence and surface w inds greater than 30kts (Tango)
Moderate Icing (Zulu)
Valid for 6 hours
SIGMET? Issued? Valid? Why are they issued?
Significant Weather Information
Issued for: Severe Turbulence not associated with T-storms
Widespread dust storms and volcanic ash
Severe Icing
Valid for 4 hours
CONVECTIVE SIGMET? Issued? Valid? Why issued?
Issued for thunderstorm (convective) activity
Winds greater than 50 kts
Hail greater than ¾”
Winds and Temperatures aloft Forecast?
Issued twice a day every 12 hours and provide wind and temperature information for specific areas within the U.S.
How are temperatures above 24,000 identified?
Temperature above 24000 feet are negative
What does 710556 mean on a Winds and Temperatures Aloft Forecast if the forecast level is 30,000 feet?
Winds are from 210 at 105 kts and temperature is –56 C
Winds will not be forecast within how many feet of station elevation on an FD?
1500’
Temperatures will not be forecast within how many feet of station elevation?
2500’
Discuss the Surface Analysis Chart? Issued? Valid? Information?
Issued 8 times daily and valid for 3 hours
Shows position of pressure systems, fronts, local weather, wind speed and directions, and visual obstructions.
Discuss the Significant Weather Prognostic Chart? Issued? Valid? Info?
Forecast of aviation weather hazards such as icing, freezing levels, and turbulence
Issued 4 times a day there is a 12 hour forecast and a 24 hour forecast
