Scientists look to cloud tops for faster severe-storm predictions

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    NOAA's GOES satellite delivered this image of clouds over the continental US at 9:45 p.m. EDT on June 18. The infrared image allows forecasters to estimate temperatures for clouds, with the darkest colors representing cloud tops with the coldest temperatures. The coldest cloud tops typically are associated with severe thunderstorms. You can see that relationship by moving to the next image.
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Severe thunderstorms can be nasty beasts. Intense lightning, hail, high winds, torrential rain, and at worst, tornadoes top the list of severe storms' more, er, stimulating features.

Now, two scientists at the University of Wisconsin's Cooperative Institute for Meteorological Satellite Studies say they have figured out a way to dramatically improve forecasters' ability to predict which seemingly run-of-the-mill storm cells are likely to go postal.

Essentially, they use infrared images from weather satellites to give forecasters as much as 45 minutes earlier notice that a severe thunderstorm is brewing than the forecasters currently can get if they only used radar or reports from storm spotters.

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Tools like this would be valuable enough today as a way to help improve severe-weather warnings. Their value likely would increase as the country copes with global warming.

Earlier this week, the US Global Change Research Program released its latest assessment of global warming's recent and future effects on the country. An increase in extreme weather, including more intense downpours, are among the conditions the assessment's authors included.

The key to the duo's approach lies in what happens to cloud-top temperatures as routine, puffy cumulus clouds begin to build into towering, anvil-shaped thunderheads. The clouds build as warm moist air rises and cools, causing the water vapor in the air to condense into cloud droplets. The act of condensing releases heat into the surrounding air. This warms it, and if the warming is sufficient, that warm air continues to rise, drawing more warm, moist air up from below. The cloud continues to grow in height.

But the water droplets themselves are cool, and those roiling around at the cloud top get colder as the cloud builds.

So University of Wisconsin researcher Wayne Feltz and Tim Schmit, a scientist with the National Oceanic and Atmospheric Administration, designed a computer program that takes high-speed satellite scans of the cloud tops and turns the data into a kind of flip book. The computer program looks for rapid rates of cooling. Those rapid rates suggest that convection within the cloud formation is picking up steam and could turn an increasingly chummy collection of summer-afternoon puff balls into a severe storm.

"We are looking for transitions," Dr. Feltz explains. "Does the cloud top consist of liquid water that is cooling rapidly? That could signal a possible convective initiation."

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