CHAPTER 4 Aviation Weather Related To IFR Flying Flashcards
What causes weather?
Weather is primarily caused by heat exchanges in the atmosphere and the surface due to temperature differences.
What are isobars?
Isobars are lines connecting points of equal pressure.
What do closely spaced isobars indicate?
Strong winds.
What do widely spaced isobars indicate?
Lighter wind on surface charts.
What is the Pressure Gradient Force (PGF)?
The force that causes winds to migrate from high to low pressure areas.
What does the Coriolis force do?
Deflects air to the right in the Northern Hemisphere and left in the Southern Hemisphere.
What is the effect of friction force on wind?
It slows the wind due to obstructions to wind flow.
What is an air mass?
A body of air with uniform moisture and temperature properties.
What is a front?
A boundary or transition zone between two air masses.
What are the four main types of fronts?
- Cold Front
- Warm Front
- Stationary Front
- Occluded Front
What happens when flying across a front?
Pilots will experience a change in winds and usually temperature.
What is a squall line?
Non-frontal lines composed of active, steady-state thunderstorms.
What does lapse rate indicate?
The rate of temperature fluctuation relative to the increase in altitude.
How can a pilot use the ambient lapse rate?
To measure air stability.
What is the average dry adiabatic lapse rate?
About 3°C for every 1,000 feet gained of altitude.
What are the three ingredients required for precipitation?
- Water vapor
- Sufficient lift
- Growth process for droplets
How is cloud formation determined?
By the stability of the air.
What are the different types of clouds based on height?
- Low clouds: Surface - 6,500 feet
- Middle clouds: 6,500 - 13,000 feet
- High clouds: 10,000 - 25,000 feet
Which cloud formation is characteristic of turbulence?
Cumulus clouds.
What are Altocumulus Standing Lenticular clouds (ACSL)?
Clouds that extend downwind of a mountain and indicate very strong turbulence.
Which clouds contribute to structural icing?
Low clouds.
Under what conditions does structural icing develop?
In the presence of large supercooled water droplets, moisture, and high humidity.
What are the three types of structural icing?
- Rime
- Clear
- Mixed
What is freezing rain?
Precipitation that instantly freezes into ice upon impact.
Define wind shear.
Sudden changes in wind velocity.
What are microbursts?
Small, short-lived, intense downbursts that produce strong winds.
What are the three stages of a thunderstorm?
- Cumulus Stage
- Mature Stage
- Dissipating Stage
What are embedded thunderstorms?
Thunderstorms found within layers of clouds that are more hazardous.
What is the proper procedure for exiting a thunderstorm?
Make a shallow 180-degree turn back to where you came from.
Compare stable air versus unstable air.
- Stable Air: Stratiform clouds, Continuous precipitation, Smooth air, Poor visibility
- Unstable Air: Cumulus clouds, Showery precipitation, Turbulent air, Good visibility
When should one expect fog?
When there is a temperature-dew point spread of at most 3 degrees Celsius.
What is dewpoint?
The temperature air must be cooled to condense into water.
What are common types of fog?
- Advection fog
- Radiation fog
- Upslope fog
- Precipitation-Induced/Frontal fog
- Steam fog
- Freezing fog
What is Flight Service?
Provides pilots with weather briefings, en route weather advisories, processes flight plans.
What does METAR stand for?
Aviation Routine Weather Report.
How long is a METAR valid?
One hour.
When are PIREPs issued?
When pilots experience unforecast weather conditions.
What are PIREPs?
Pilot reports filed by pilots experiencing weather conditions not forecasted such as icing or turbulence.
PIREPs are issued upon receipt and include essential data like routine or urgent status, location, time, flight level, and type of aircraft.
What data is required in a PIREP?
- UA - Routine or UUA – urgent
- OV - Location of the PIREP
- TM - Time the PIREP was received from the pilot
- FL - Flight level or altitude above sea level of the PIREP
- TP - Type of aircraft
These data points are critical for understanding the context of the report.
How can pilots obtain PIREPs?
Pilots can obtain PIREPs individually or as part of a surface aviation weather report via 800-WX-BRIEF or 1800WXBRIEF.com.
PIREPs can be accessed in the Synopsis and Current Weather section.
What does ASOS stand for?
Automated Surface Observation System.
ASOS provides up-to-date weather observations and is the primary surface weather observation system in the United States.
What is the purpose of AWOS?
Automated Weather Observation System used at selected airports for providing automated weather reports.
AWOS reports include ceiling, visibility, temperature, wind conditions, and more.
What is a TAF?
Terminal Area Forecast outlining expected meteorological conditions for a specific time period.
TAFs cover the airport and surrounding 5 statute miles.
How long are TAFs typically valid?
Usually 24 hours, except for designated high-impact airports where they are valid for up to 30 hours.
How often are TAFs issued?
Four times daily.
What does the Graphical Forecast for Aviation (GFA) provide?
Graphic depictions of weather conditions for pilots, including winds, turbulence, icing, ceilings, and visibility.
GFA allows pilots to visualize weather impacts on flight.
What are Winds and Temperatures Aloft Forecasts?
Forecasts updated four times daily showing wind direction and speed for selected flight levels.
What does a wind speed of less than 5 knots indicate in forecasts?
Expressed as 9900.
How can wind and temperature forecasts assist pilots?
- Determine most favorable altitude for flying
- Identify areas of possible icing
- Recognize temperature inversions
- Anticipate turbulence
What is a Prognostic Chart?
A forecast chart issued four times daily providing a 12-hour and 24-hour weather forecast for the CONUS up to 24,000 feet.
It is commonly used for flight planning below 24,000 feet.
What is a Convective SIGMET?
Issued for thunderstorm activity and severe turbulence, icing, and wind shear conditions.
When can a Convective SIGMET be issued?
- A line of thunderstorms at least 60 miles long affecting 40% of its length
- Embedded or severe thunderstorms expected for over 30 minutes
- Active thunderstorms impacting aircraft safety along 40% of the area
What conditions warrant a Nonconvective SIGMET?
- Severe icing
- Severe turbulence
- Widespread dust storm
- Widespread sandstorm
- Volcanic ash
What are AIRMETs?
Airmen’s meteorological information issued for conditions less severe than SIGMETs.
What conditions do AIRMET reports describe?
- Ceiling less than 1,000 ft and/or visibility less than 3 SM
- Moderate icing and/or turbulence
- Sustained surface winds at least 30 knots
- Nonconvective LLWS potential below 2,000 ft AGL
- Widespread mountain obscuration
What are the three types of AIRMETs?
- AIRMET Sierra - IFR conditions and/or mountain obscurations
- AIRMET Tango - Turbulence/strong surface winds
- AIRMET Zulu - Icing
