PRIMUSr 880 Digital Weather Radar System
On reaching the tropopause, the hail is ejected from the storm and falls downward to a point where it is sucked back into the storm. When the hail falls below the freezing level, however, it begins to melt and form a thin surface layer of liquid detectable by radar. A slight downward tilt of the antenna toward the warmer air shows rain coming from unseen dry hail that is directly in the flightpath, as shown in figure 5- 36. At lower altitudes, the reverse is sometimes true; the radar may be scanning below a rapidly developing storm cell, from which the heavy rain droplets have not had time to fall through the updrafts to the flight level. Tilting the antenna up and down regularly produces the total weather picture.
Using a tilt setting that has the radar look into the area of maximum reflectivity (5000 to 20,000 ft) gives the strongest radar picture. However the tilt setting must not be left at this setting. Periodically, the pilot should look up and down from this setting to see the total picture of the weather in the flightpath.
Often, hailstorms generate weak but characteristic patterns like those shown in figure 5- 37. Fingers or hooks of cyclonic winds that radiate from the main body of a storm usually contain hail. A U shaped pattern is also (frequently) a column of dry hail that returns no signal but is buried in a larger area of rain that does return a strong signal. Scalloped edges on a pattern also indicate the presence of dry hail bordering a rain area. Finally, weak or fuzzy protuberances are not always associated with hail, but should be watched closely; they can change rapidly.
DRY HAIL 
BEAM IN
DOWNWARD
TILT POSITION
WET HAIL 
AND RAIN
AD- 12059- R1@
Rain Coming From Unseen Dry Hail
Figure 5- 36
A28- 1146- 102- 00 | Radar Facts |
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