A severe squall line formed over eastern Texas on 25 January 2012. There were 19 tornado reports and 48 reports of wind damage, including “a house destroyed by a possible downburst”, according to the Storm Prediction Center. The high resolution imager on VIIRS captured this squall line as it was rapidly intensifying. Shown below are images collected from channel I-5, the high-resolution infrared window channel (11.45 μm). (Click on images for full resolution.)
This squall line had several overshooting tops over the Gulf of Mexico that reached a temperature of -77 C. A zoomed-in view of these tops are shown below.
The dark blue pixels near the center of the image indicate an overshooting top approximately 5 km in diameter where temperatures were less than -77 C. Several pixels in a storm top at the bottom center of the image and in a storm top at the top center of the image (near Galveston, TX) also reached that temperature.
A sounding was taken at 18:00 UTC at the Lake Charles, LA, National Weather Service (NWS) office, which observed a minimum temperature of -74 C at 17.9 km above sea level, indicating that these are some tall thunderstorms. Image courtesy the University of Wyoming.
The VIIRS imagery was collected right as the squall line was intensifying. Shown below is the radar loop from the Houston/Galveston radar between 18:00 UTC and 21:00 UTC. Note, at the beginning of the loop, the southern end of system consists of two rather disorganized lines of cells. These lines of cells merge at around 19:25 UTC (the time of the Suomi NPP overpass), and a much stronger and more organized squall line develops.
At roughly 375-m resolution at nadir, the I-5 channel on VIIRS is providing some of the highest resolution infrared imagery available to the atmospheric science community. We are just beginning to see the capabilities of this powerful instrument.