Cooler temperatures limit severe weather

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Scientists at the University of Alabama at Huntsville recently released their analysis of the global temperatures in March. The map shows how the temperatures in the lower troposphere – the layer of the atmosphere closest to the ground – compared to seasonal norms. The blue tones represent cooler-than-average temperatures, and the yellow and orange tones represent warmer-than-average temperatures.

The light blue draped from the west coast to the northeast coast of the United States should not be too surprising to most of us. Much of the month was on the cool side, and in the Northern Plains and Upper Midwest, it was downright wintry. While most of us spent the month looking forward to warmer weather and outdoor spring activities, those that despise severe weather might not have minded the prolonged chill.

Severe storms require a great amount of energy to get going, and warmth equals energy. When forecasting thunderstorms, meteorologists look at something called CAPE, which stands for Convective Available Potential Energy. It’s one of the measurements that tell us how unstable the atmosphere may be on a particular day. Usually, in order to see the greatest amount of instability and have the best chance for storms, we need to surpass a certain temperature at the ground level. So, the warmer the surface temperature gets, the more likely we’ll see thunderstorms develop.

There are other factors in thunderstorm development, and even more for severe storms to develop, which I’ll save for future posts. My point here is to say that the cooler temperatures across much of the country during March, with the exception of the deep southern and southeastern states, kept severe weather at bay.

As we head into April, it’s likely that we’ll start to see an uptick in thunderstorm potential. The Climate Prediction Center is forecasting above-average chances for the temperatures across most of the nation to be above normal. While I don’t always agree with its predictions, I don’t see much reason to doubt this one.

As a point of reference, today’s average high temperature at RDU International Airport is 69 degrees, and today’s average low is 45.