12-42GTN 725/750 Pilot’s Guide 190-01007-03 Rev. CForewordGettingStartedAudio &Xpdr CtrlCom/NavFPLDirect-ToProcChartsWpt InfoMapTrafflcTerrainWeatherNearestServices/MusicUtilitiesSystemMessagesSymbolsAppendixIndex12.3.5.3 TornadoesThere is no conclusive radar target return characteristics which will identifya tornado, however, tornadoes may be present if the following characteristicsare observed:• A narrow, finger-like portion, as shown on the previous page, extends and,in a short time, curls into a hook and closes on itself.• A “hook” which may be in the general shape of the numeral “6,” especiallyif bright and projecting from the southwest quadrant (northeast quadrant inthe southern hemisphere) of a major thunderstorm.• V- shaped notches.• Doughnut shapes.These shapes do not always indicate tornadoes, nor are tornado returnslimited to these characteristics. Confirmed radar observations of tornadoes mostoften have not shown shapes different from those of a normal thunderstormdisplay.12.3.5.4 HailHail results from updrafts carrying water high enough to freeze. Therefore,the higher the top of a thunderstorm, the greater the probability that it containshail. Vertically scanning the target return can give the radar top of a thunderstormthat contains hail. Radar top is the top of a storm cellas detected by radar. It isnot the actual top, or true top of the storm. The actual top of a storm cell is seenwith the eyes in clear air and may be much higher than the radar top. The actualtop does not indicate the top of the hazardous area.Hail can fall below the minimum reflectivity threshold for radar detection.It can have a film of water on its surface, making its reflective characteristicssimilar to a very large water droplet. Because of this film of water, and becausehail stones usually are larger than water droplets, thunderstorms with largeamounts of wet hail return stronger signals than those with rain. Some hailshafts are extremely narrow (100 yards or less) and make poor radar targets. Inthe upper regions of a cell where ice particles are “dry” (no liquid coating), targetreturns are less intense.Hail shafts are associated with the same radar target return characteristicsas tornados. U-shaped cloud edges 3 to 7 miles across can also indicate hail.These target returns appear quite suddenly along any edge of the cell outline.They also change in intensity and shape in a matter of seconds, making vigilantmonitoring essential.
