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Air Mass Thunderstorms
Air mass thunderstorms are ordinary thunderstorms produced within an unstable air mass by local convection. Most of them are multicell storms that go through the
three stages of development in an hour or less. They are of relatively brief duration because their own precipitation cuts off their energy sources by increasing
downdrafts which reduce humid updrafts.
Air mass thunderstorms are normally not evident at KNPA before May. They form in the unstable mT air, are generally less severe, and as a rule extend to lower
heights than frontal thunderstorms. Due to an absence of convergent airflow during the winter, convective thunderstorms are rare. The most severe air mass
thunderstorms may have surface wind gusts in excess of 50 knots, but generally only produce maximum wind gusts of 35 to 40 knots.
KNPA is not directly affected by air mass thunderstorms a majority of the time, even though they are frequently within 25 nm of the field. The most prolific area for
development is northwest of a line from Innerarity Point through Pleasant Grove to the Ensley subdivisions. The prevailing direction of movement is northeastward at
5-10 knots.
A reliable forecast for movement of air mass thunderstorm cells in the near vicinity may be made using the direction of the 700 mb winds and the speed of the 850
mb winds.
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