Archive for February, 2008

Wildfires in Texas

Wednesday, February 27th, 2008

GOES-12 3.9µm IR images (Animated GIF)

Several large wildfires began to burn across parts of western Texas (and also southeastern New Mexico) late in the day on 25 February 2008, as seen by the large number of fire “hot spots” (black to red pixels, with red being the hottest temperatures) on GOES-12 3.9 µm “shortwave IR” images (above). Strong northerly winds — gusting as high as 67 mph (30 m s-1) at Guadalupe Pass, 51 mph (23 m s-1) at Midland, and 45 mph (20 m s-1) at San Angelo — helped the grass fires quickly grow out of control and spread rapidly southward; this extreme fire growth was evident by the fast rate of increase in areal coverage of “hot” black-to-red pixels on the shortwave IR imagery. Very warm surface air temperatures were also noted across Texas on that day, with a high of 93º F (34º C) at San Angelo and a high of 99ºF (37º C) at Del Rio (which tied the all-time record high for the month of February at that location).

MODIS + GOES-12 shortwave IR images

A comparison of the 1-km resolution MODIS 3.7 µm IR image with the corresponding 4-km resolution GOES-12 3.9 µm IR image (above) as the fire intensity and coverage was beginning to diminish around 05:00 UTC or Midnight local time (near the end of the GOES-12 shortwave IR animation shown at the beginning of this post) demonstrates the superior fire detection capability offered by the improvement in spatial resolution on the MODIS instrument. The largest of the active fires was located to the west/northwest of San Angelo (station identifier KSJT), and hot pixels associated with this large fire (black to red enhancement) could be seen across parts of several different counties.

MODIS true color image (Google Earth)

An extensive burn scar resulting from the largest fire (the “Glass Fire”, which was located between San Angelo and Midland) was apparent on MODIS true color imagery (viewed using Google Earth, above) two days later (on 27 February 2008). In fact, one small fire was still burning along the southeastern periphery of the burn scar, with a subtle smoke plume seen drifting northeastward toward Highway 87. The Glass Fire burned over 219,000 acres in Sterling county alone (InciWeb).

Cloud features related to sharp sea surface temperature (SST) gradients

Tuesday, February 26th, 2008

GOES-12 visible images (Animated GIF)

Some interesting cloud features were seen in the western North Atlantic Ocean on 26 February 2008, about 300 miles southeast of New England (and about 300 miles south of Nova Scotia, Canada): a narrow line of cumulus clouds (oriented approximately north-south), and a patch of stratus cloud (or possibly fog?) that developed just east of the cumulus line. These cloud features were apparently related to very sharp gradients in the Sea Surface Temperature (SST) over that particular area.

GOES-12 10.7µm IR images (Animated GIF)

AWIPS images of the GOES-12 10.7µm IR channel (above) showed that there were large cold eddies (darker green enhancement) located over the western North Atlantic, along the north wall of the Gulf Stream (RTG_SST analysis). These cold water eddies remained stationary as patches of colder clouds (cyan to blue enhancement) drifted eastward across the region.

MODIS sea surface temperature (SST) product

An 8-day composite of the MODIS Sea Surface Temperature product (above) confirmed the presence of a very sharp SST gradient in that area (near 40º N latitude, 65º W longitude), with a patch of water having SST values in the 40s F (cyan to blue enhancement) located just to the east of water having SST values in the 60s F (green enhancements) — black features on the SST image are clouds. Low-level baroclinicity enhanced by the sharp SST gradient was aiding the development and maintenance of the cumulus line; as warm air moving eastward encountered the colder pocket of water, stratus cloud quickly formed as the marine boundary layer air was rapidly cooled to its dew point.