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A squall line over Texas as seen by VIIRS

Posted On: February 6, 2012 - By: Curtis Seaman


VIIRS RGB "true color" composite

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.)

VIIRS Channel I05

A squall line over eastern Texas observed by VIIRS channel I05 (11.45 um) at 19:24 UTC on 25 January 2012.

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.

VIIRS Channel I05

A squall line over eastern Texas observed by VIIRS channel I05 (11.45 um) at 19:24 UTC on 25 January 2012.

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.

Radiosonde sounding

NWS sounding taken at 18:00 UTC from the Lake Charles, LA office.

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.

Radar loop

Radar loop from the Houston/Galveston NWS WSR-88D radar beginning at 18:00 UTC, 25 January 2012.

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.


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