The largest outbreak of severe weather so far this season developed across a large portion of the central US on 04 May / 05 May / 06 May 2007, producing tornadoes from Texas to South Dakota, hail up to 4.25 inches in diameter in Nebraska, and wind gusts to 90 mph in Kansas. GOES-12 images of the 10.7µm InfraRed (IR) channel (above; QuickTime animation) show the development of the severe convection that spawned the deadly EF-5 tornado that destroyed much of Greensburg, Kansas (located near the center of the images) around 02:38 UTC on 05 May (9:38 PM on 04 May, local time). This was the first F5/EF-5 tornado damage in the US since May 1999.

One striking aspect of the IR satellite imagery on 06 May was the large areal coverage of unusually cold cloud top temperatures (colder than -80º C, purple enhancement) early in the day over eastern Nebraska and western Iowa (above; QuickTime animation). A comparison of 1-km resolution NOAA-18 IR and 4-km resolution GOES-12 IR (below) reveals cloud top temperatures as cold as -87º C (-125º F) and -85º C (-121º F), respectively; such a close agreement between AVHRR vs. GOES IR temperatures is also somewhat unusual, since the higher spatial resolution of the AVHRR instrument often senses cloud top temperatures that are as much as 10-20º C colder than GOES in the areas of convective storm tops.

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While the large (472,000 acre) Sweat Farm Road / Big Turnaround fire complex continued to burn for the 17th consecutive day south of Waycross, Georgia, a second fire (the 6000-acre Roundabout fire west of Waycross) was also beginning to produce very thick smoke on 02 May 2007. GOES-12 visible imagery (above; Java animation) showed the transport of the smoke — many surface stations reported smoke or haze across southeastern Georgia, northeastern Florida, and far southeastern South Carolina that day (and EPA AIRNow particle Air Quality Indices were in the “Moderate” to “Unhealthy for Sensitive Groups” category). It is interesting to note that parts of the smoke pall were thick enough to reduce surface heating to the point that afternoon cumulus cloud formation was inhibited — a similar effect was discussed a few days earlier on the UMBC “US Air Quality” blog.

The MODIS aerosol optical depth (AOD) product from the IDEA site (below) indicated very high AOD values of 0.8 to 1.0. The 02 May IDEA trajectory forecast suggested that much of this smoke would experience a local recirculation during the following 24-48 hours, along with a transport of some smoke northeastward along the coastal portions of South Carolina and North Carolina. The MODIS AOD product and MODIS visible imagery from the next day (03 May 2007) verified this forecast, with thick smoke remaining over the general source region, in addition to a filament of smoke reaching as far northeastward as the outer banks of North Carolina.

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An animation of 3-hourly water vapor channel image composites from AWIPS during the entire month of April 2007 (25.5 MB QuickTime animation; 1280×1024 screen resolution required) shows the diverse variety of synoptic scale features that affected the Northern Hemisphere during that particular month.

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The Sweat Farm Road / Big Turnaround fire complex (that started on 16 April 2007) has become the largest wildfire in Georgia history, burning over 472,000 acres so far. A series of daily (21:45 UTC) GOES-12 visible images (above) shows that the smoke plume drifted in different directions on various days due to shifting winds. A similar series of daily (21:45 UTC) GOES-12 3.9µm IR images (below) indicated that this was also a very hot fire (darker pixels = hotter brightness temperatures) — on many days the IR images revealed a saturation of the GOES-12 shortwave IR detectors (causing the temperature of the fire pixels to “roll-over” and be displayed as “cold” white pixels). The fire appeared to diminish somewhat on 27 April (note the smaller smoke plume and less intense fire hot spot on that day), but then it intensified the following day (and another new fire started just to the northwest).

A 3-channel red/green/blue (RGB) composite image using the Terra MODIS channels 07, 02, and 01 (below) shows the large size of the resulting burn scar that covered a significant portion of the southern half of Ware county Georgia on 30 April. The active fires that were still burning on that day were evident by the red-colored “hot spots” along the southeastern edge of the burn scar — the leading edge of the active fires had moved southward into extreme northern Charlton county. The new fire that started just to the northwest (in Atkinson county) a day earlier was also exhibiting a pronounced hot spot and smoke plume.

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