Figure 5-12.-Suggested checklist for the determination of air mass thunderstorm activity—Continued.
with their most frequent occurrence during May. The
season of occurrence varies with the locality. In the
United States, 80 percent of the tornadoes have occurred
between noon and 2100 local time.
Complete details on the forecasting of these
phenomena are beyond the scope of this training
manual. You should consult the U.S. Department of
Commerce, Forecasting Guide No. 1, Forecasting
Tornadoes and Severe Thunderstorms, and the many
other excellent texts and publications for a complete
understanding of this problem.
The senior
Aerographer’s Mate should have a basic understanding
of the factors leading to the formation of such severe
phenomena, to recognize potential situations, and to be
able to forecast such phenomena.
SURFACE THERMAL PATTERNS AS A
FORECASTING AID
This method indicates that thermal tongues
averaging 50 miles or less in width are favored locations
for tornado activity within the area of convective storm
activity. These thermal tongues can be located quite
readily on the surface synoptic chart. Use the following
technique to supplement the existing tornado forecast.
The procedures to locate areas of potentially severe
convective activity with reference to the synoptic
surface thermal pattern are as follows:
1. Draw isotherms for every 2°C to locate thermal
tongues.
2. Within the general area in which convective
storms are forecast, locate the axis of all pronounced
5-17
