JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
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, of
course, experiencing vivid lightning or tornado-like activity.
If you suspect the potential for wind shear conditions prior to take off 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 ⅔ of the
thunderstorm cell. Note that the actual altitude of the freezing level will fluctuate with the up and
down drafts, and it will 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 were covered in more
detail in Chapter 4.
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.
Detection and warnings are more accurate with the modern NEXRAD Doppler radar systems
(Figure 5-8). This is particularly true for microbursts and wind shear alerts.
Version 3.2/Dec 08 5-7