Summertime thunderstorms-here, there, but NOT everywhere

July 24, 2007 at 6:37 pm | Posted in Uncategorized | Leave a comment

Summertime late afternoon and early evening thunderstorms are a staple this year.

To make a thunderstorm, in any season, you need three things:
1. Deep Moisture (humidity in the atmosphere at the surface, and upward a few thousand feet)
2. Instability (once upward motion starts in the atmosphere, it will continue)
3. Trigger (something to start the upward motion)

Normally, during spring severe weather, the trigger is something like a cold front, or dryline. But in the summer, we have to have heat from the sun start upward motion in the atmosphere. Often times, the atmosphere is only moderately unstable, or is only unstable in a few spots. As the sun starts the heating, the first storms go up in the spots of highest instability.

Once the storms develop, they move slowly, and thanks to no strong upper level support, they often times rain down into their own updraft, choking off the storm after 45-60 minutes. As the rain cooled air falls to the ground, it hits and spreads out, acting as a “mini-front” and causing new storms to develop.

Also, storm clouds are big and thick, and block the sun, this can limit the instability in areas that are shaded by the storms-that may lower the rain chances a bit (unless that “mini-front” of rain cooled air is enough of a trigger)

Often times, only subtle differences in the summer mean one area gets thunderstorms and one area stays dry. Take Monday afternoon, Denton and Tarrant Counties got pounded, but most of Collin and Dallas Counties stayed dry!


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