#weatherinaminute What is an air-mass thunderstorm?

Weather Lessons With Ashley

Tonight, we had a late day thunderstorm pop up over Birmingham. It ended with quickly rising waters and a water rescue as a car drove into water that was covering a downtown road. Fortunately, there were no reported injuries.

We often hear the phrase, “it came out of no where!” or “I had no idea we were even going to get rain today” and the trickiest part of forecasting summer-time storms is location. We know they will happen, we even know generally when they will happen (heat of the day: late afternoon-early evening), but pin pointing where these storms materialize is the real challenge.

Tonight, the thunderstorm that bubbled up over Jefferson County provided some great views from surrounding communities.

This cloud formation is what is known as an air-mass thunderstorm. The difference between an air-mass thunderstorm and a severe storm is that air-mass storms do not rotate.

What we see is a distinct updraft, which is rising air carrying clouds up to the stratosphere. When the cumulonimbus clouds reach the stratosphere, they spread out and form an anvil-looking cloud. Also, the anvil tells us where storms are heading. They are pointing in the direction that the upper level jet stream is going. That’s pretty cool!

In this picture, we also see the downdraft, depicted by the cluster of puffy clouds and rain column just behind the trees. This is where the storm is collapsing and heavy rain is falling. In this area is where flash flooding and gusty winds can occur. This is also the area of a thunderstorm where hail will fall. The downdraft creates rain cooled air, by evaporative cooling, and eventually it overtakes the updraft and turns off the ability for the storm to grow any more.

At this point, the thunderstorm goes from a mature stage to its dissipating stage. The rain goes from intense to light. The winds go from strong to weak. The clouds even shrink in size.

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