A wildfire was set by arsonists in the Hollywood Hills near Hollywood, California on the afternoon of 30 March 2007. GOES-12 visible channel imagery (above; Java animation) shows the smoke plume that drifted south/southwestward; corresponding GOES-12 3.9µm InfraRed (IR) imagery (Java animation) revealed a local “hot spot” associated with the fire. The CIMSS GOES-11 Wildfire ABBA product (below) detected a “Processed Fire” (red pixel) as early as 20:30 UTC (1:30 PM local time); a 250-meter resolution Aqua MODIS true color image showed the early stages of the smoke plume at 20:47 UTC (1:47 PM local time).

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An IDEA MODIS Aerosol Optical Depth (AOD) image (above) depicted elevated AOD values of 0.6 to 0.8 over parts of the Southeast US (especially the northern half of Georgia) on 29 March 2007. Smoke from recent fire activity was likely the main contributor, but some of the elevated AOD signal may also have been due to very high pollen counts in that region — pine tree pollen has been unusually high this Spring season due to abnormally dry conditions that have plagued much of the southeastern US. In addition, light winds and increasing boundary layer moisture were helping to create an environment favorable for particle pollution growth — GOES sounder total precipitable water values of 25-35 mm were becoming more common over that particular region (below).

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A major outbreak of severe convection developed across the southern and central Plains states during the day on 28 March and 29 March 2007; large and long-lived thunderstorms produced widespread tornadoes (including fatal tornadoes in Texas and Oklahoma, and the first tornado-related fatality in Colorado since 1960), large hail (up to 4.5 inches in diameter in Texas), and damaging winds (28 March SPC storm reports). An AWIPS image of the MODIS 11.0µm InfraRed (“IR window”) channel with overlays of cloud-to-ground lightning strikes and surface wind streamlines (above) shows the large density of lightning strikes (1587 negative strikes and 61 positive strikes in a 15-minute period) that was generally aligned along a cold frontal boundary that was moving eastward across the Texas panhandle region. If we examine the MODIS IR image without any overlays (below), we see that there were 2 examples of a subtle “warm trench” signature (a ring of warmer cloud top temperatures surrounding the coldest temperatures associated with the overshooting tops) — this satellite signature suggests that there may have been some compensating subsidence immediately surrounding the vigorous overshooting tops as they penetrated the tropopause level. You can get a sense that such a “trench” can surround an overshooting top by examining astronaut photography of thunderstorms taken from the space shuttle (image courtesy of Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center). QuickTime animations of rapid-scan GOES-11 10.7µm IR images centered on Lubbock, Texas and Goodland, Kansas show large and persistent enhanced-v signatures exhibited by many of these storms.

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Widespread severe convection developed during the day on 23 March 2007 over parts of New Mexico, Texas, Oklahoma, Kansas, and Colorado. AWIPS imagery of the MODIS and GOES InfraRed (IR) and water vapor channels (above) indicates that six of these storms located over eastern New Mexico and the Texas/Oklahoma panhandle region exhibited “enhanced-v” signatures around 20:30-20:38 UTC (the enhanced-v signatures were better defined on the 1-km resolution MODIS images, compared to the 4-km resolution GOES images). This particular satellite signature is an indicator that thunderstorms are producing (or are about to produce) hail, tornadoes, or damaging winds. According to the SPC storm reports, the storms were indeed producing hail up to 1.75 inches in diameter in New Mexico around the time of the images above; hail up to 2 inches in diameter and several tornadoes were then reported within 1-4 hours of the image time.

A vigorous upper-level cutoff low was located over the Baja California region at 12 UTC that day. AWIPS imagery of the GOES sounder total column ozone product (below) depicted elevated ozone levels (green enhancement) within a broad tropopause anomaly in the vicinity of the upper low — the height of the 1.5 Potential Vorticity Unit (PVU) surface (which defines the dynamical tropopause) was as low 475 hPa . Dynamic forcing associated with this low began to increase over the southwestern US as the cutoff low moved northeastward during the day.

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