Icing - P-3030092

CHAPTER FOUR

AVIATION WEATHER

Visual cues are also very important in detecting microbursts. In fact, in many fatal wind shear

mishaps the pilot continued the approach or takeoff in visible and known thunderstorm

conditions. Visual cues include virga, localized blowing dust (especially in circular or elliptical

patterns), rain shafts with rain diverging away from the core of the cell, roll clouds, and

experiencing vivid lightning or tornado-like activity.

If you suspect the potential for wind shear conditions prior to takeoff or landing, get additional

information from the tower or base weather station to include the latest radar report and pilot

reports (PIREPs). Some airfields even have a wind shear warning system to help you. These

sources will not identify every microburst situation, so if in doubt, wait it out! If you do

encounter a wind shear condition, you must make a PIREP to warn fellow aviators about the

dangerous situation. Your PIREP should include the location where the activity was

encountered, an estimate of its magnitude and, most importantly, a description of what was

experienced, such as turbulence, airspeed gain or loss, glidepath problems, etc.

Icing

Expect severe icing in thunderstorms where the free-air temperature is at or below freezing.

Since heavy rainfall and turbulence most frequently occur at the freezing level, this particular

altitude appears to be the most hazardous. Most of the icing, however, occurs in the top 2/3 of

the thunderstorm cell. Note that the actual altitude of the freezing level will fluctuate with the up

and downdrafts, and be lower in the area of downdrafts. Due to the heavy amounts of moisture

and large water droplets, the icing in thunderstorms is mostly clear icing, accumulating rapidly

on the airfoils and other aircraft surfaces. Other aspects of icing will be covered in more detail in

Chapter Five.

407.

RADAR THUNDERSTORM INFORMATION

Ground-based weather radar is the most accurate means of tracking thunderstorms. In addition

to the locating and tracking of cumulonimbus cells, their intensities can also be determined. The

large drops of water and hail, if present, within thunderstorms yield the strongest return signals.

Smaller droplets result in dimmer areas on the scope and snow produces the faintest echo.

4-10 Thunderstorms