Garmin Appliance Data User's Guide download pdf (Page 116)

104 190-00607-02 Rev D

Detailed Operation

Tornadoes

There is no conclusive radar target return charac-

teristics which will identify a tornado, however, torna-

does may be present if the following characteristics are

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, especially if bright and projecting

from the southwest quadrant (northeast quadrant

in the southern hemisphere) of a major thunder-

storm moving eastward.

• V- shaped notches

• Doughnut shapes.

These shapes do not always indicate tornadoes,

nor are tornado returns limited to these characteris-

tics. Conﬁrmed radar observations of tornadoes most

often have not shown shapes different from those of a

normal thunderstorm display.

Hail

Hail results from updrafts carrying water high

enough to freeze. Therefore, the higher the top of a

thunderstorm, the greater the probability that it con-

tains hail. The height can be determined by vertically

scanning the target return.

Hail usually has a ﬁlm of water on its surface

making it’s reﬂective characteristics similar to a very

large water droplet. Because of this water ﬁlm, and

because hail stones usually are larger than water drop-

lets, thunderstorms with large amounts of wet hail

return stronger signals than those with rain. Some hail

shafts are extremely narrow (100 yards or less) and

make poor radar targets. In the upper regions of the

cell, where ice particles are “dry” (no liquid coating),

target returns are less intense.

Hail shafts are associated with the same radar target

return characteristics as 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 vigilant monitor-

ing essential.

Radar

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