Physics Photo of the Week

April 17, 2009

2 Storms
Friday, April 10, 2009 was a stromy day in the southeastern United States.  The satellite photo for 16:45 UTC (12:45 pm EDT) shows two storms in N. Carolina and Tennessee - the dense yellow parts of the image.  These images were made by an infrared sensor on a geostationary NASA satellite.  The infrared sensor has two advantages: 1) cloud images can be made at night in the absence of sunlight; 2) the false colors indicate the temperatures of the cloud tops.  Yellow regions are very high altitude extreme cold cloud tops.  The presence of the high altitude cloud tops indicate extreme convection that forms thunderstorms and the accompanying severe weather.

Warren Wilson College in western North Carolina had just experienced a strong thunderstorm a few hours earlier as the first of these two storms swept by.  The second storm (west-central Tenessee in the satellite image above), however proved very bad for parts of northern Alabama and Tennessee later in the day forming highly destructive tornadoes in parts of Alabama.  The second storm swept through western North Carolina later that night, bringing over an inch of rain to Warren Wilson College - but no severe weather.  The animation at right shows the passage of the two storms through the area.  The animation is a 5 hour time lapse beginning about 11:30 am.  Notice how the second storm rapidly grew in size to cover a much larger area as it rampaged through.

These two storms were part of a complex weather pattern centered in southern Illinois.  The weather pattern circulated around a low pressure center.  The circulation brought moist air from the Gulf of Mexico and cold artic area from the northest plains.  The meeting of the warm humid gulf air and the cold air formed much precipitation, generated massive cumulus clouds and thunderstorms, and produced the violent destructive tornadoes.  The central US has more tornadoes than any other part of the world - hence the name "Tornado Alley".

The images were downloaded at the NASA interactive satellite center: which displays the current satellite images (visible, infrared, and water vapor) for any place on the Earth.  The weather satellite service provided by NASA for public use is much appreciated. 

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to 

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