The effect of the topography in western South Dakota and eastern Wyoming was very obvious on 19 March 2007, as low-altitude stratus clouds were forced to move around the higher elevation portions of the Black Hills (GOES-11 visible images: Java animation). AWIPS images of a few of the MODIS channels (above) revealed that a good deal of the cloud-free highest elevations were still snow-covered. This snow cover appeared brighter than the surrounding tree-covered (but snow-free) surface on the Band 1 visible image (above, upper left panel) — the darker appearance of that same area on the Band 7 Snow/Ice image (above, lower left panel) is a signal of snow on the ground (in contrast to the supercooled water droplet stratus cloud, which appeared much brighter on the Band 7 image). MODIS and GOES fog/stratus product images from the pre-dawn hours showed that this area of stratus cloud was forming due to upslope northerly/northeasterly flow in the wake of a cold frontal passage.

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A 500-meter resolution MODIS true color image (below) showed even better detail of the snow cover and the stratus clouds that surrounded the Black Hills. The light gray region just to the east of the stratus cloud edge is the Badlands National Park, whose sandy and rocky surface has a higher albedo than the surrounding grasslands. Snow depths at the highest elevations were still as great as 18 inches at North Rapid Creek (station NRPS2, near Rochford, South Dakota).

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GOES-11 (GOES-West) Visible (daytime) and 3.9 µm Shortwave Infrared (nighttime) imagery (above) revealed an interesting cyclonic vortex which was propagating westward across the eastern North Pacific Ocean on 13-14 March 2007. The radial banded cloud features that form such a cloud “swirl” are known as actinae or actinoform clouds, and they are occasionally seen in the marine stratocumulus cloud field over the Pacific Ocean (one such case was June 1997). This type of cloud pattern was first observed back in 1962 on TIROS V imagery near Hawaii.

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Thick fog forming in southern portions of Osceola county in Florida was a factor in causing a multiple vehicle accident along the Florida Turnpike during the morning of 13 March 2007. AWIPS images of the MODIS and GOES fog/stratus brightness temperature difference several hours before the accident (above) shows how the 1-km resolution MODIS product had better skill at depicting the location and coverage of the fog (compared to the 4-km resolution GOES product).

Smoke from small brush fires in that area on the previous day was thought to have helped to further reduce surface visibilities along with the fog; an AWIPS image of the GOES-12 3.9 µm Shortwave Infrared channel (below) shows a “hot spot” (red enhancement) associated with a fire that was burning just west of the Florida Turnpike in central Osceola county at 21:31 UTC on 12 March. The GOES-12 3.9 µm brightness temperature at that particular hot pixel was +40ºC; however, most of the brush fires in that area were apparently too small in size to produce similar hot spots at other image times, and the CIMSS Wildfire ABBA product only indicated a few brief fire pixels in central Florida during the day on 12 March.

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A very large and long-lived Mesoscale Convective System (MCS) developed over Texas during the pre-dawn hours on 12 March 2007, which produced reports of tornadoes, hail up to 2.5 inches in diameter, and damaging winds up to 95 mph (SPC storm reports). AWIPS images of the GOES-12 10.7µm InfraRed (IR) channel (above; QuickTime animation) shows the areal extent of cold cloud top temperatures associated with the developing MCS — IR cloud top temperatures were as cold as -72º C / -97º F (black enhancement) at 03:30 and 11:15 UTC. The supercell convection that first developed across the Big Bend region and over central Texas did exhibit enhanced-v signatures from about 23:00 UTC on 11 March to 03:00 UTC on 12 March.

The MCS eventually developed Line Echo Wave Pattern (LEWP) structures, which were evident in the cloud to ground (CG) lightning strike data (below; QuickTime animation) — in fact, this severe convection produced over 1000 CG strikes every 15 minutes during the 09-10 UTC period. Later in the day, new convective development produced heavy rainfall (including reports of 2.00 inches in a 1 hour period, and a total of 6.94 inches) in the Brownsville, Texas area — GOES sounder derived product imagery displayed Total Precipitable Water (TPW) values of 46 mm (1.8 inch) and Convective Available Potential Energy (CAPE) values of 2480 J/kg over that region several hours earlier.

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