Unusually hot conditions developed across parts of the Desert Southwest during the first week of July 2007 — daily maximum temperatures on 05 July included 127º F (53º C) at Death Valley, California, 122º F (50º C) at several locations within the Lake Mead/Lake Mohave basin region of Nevada/Arizona, 120º F (49º C) at Needles, California, and 116º F (47º C) at Las Vegas, Nevada (1º F shy of their all-time record high temperature). Following such hot daytime temperatures, a nighttime AWIPS image of the MODIS 11.0µm InfraRed (IR) channel (above) showed that nocturnal temperatures remained rather warm — IR brightness temperatures at 09:22 UTC (2:22 AM local time) were still 30º C / 86º F or warmer (orange to red enhancement) over a good deal of the Death Valley and Lake Mead/Lake Mohave basin regions. In fact, the official cooperative weather observation site at Death Valley (DEVC1) reported an overnight minimum temperature of 95º F (35º C), while a nearby mesonet site at Death Valley National Park (CQ162) only dropped to 105º F (41º C) at 7:00 AM local time (14:00 UTC).

An AWIPS comparison of MODIS IR, GOES imager IR, and GOES Sounder Skin Temperature (above) revealed brightness temperatures in the lowest elevations of Death Valley were still as warm as 86-96º F (30-36º C) at 09 UTC. In addition, an AWIPS image of the MODIS sea surface temperature product (below) indicated that water temperatures were as warm as 87-89º F (31-32º C) (dark red enhancement) in portions of Lake Mead and Lake Mohave.

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The large “Angora wildfire” began to burn just south of Lake Tahoe in California sometime after 21:00 UTC (1:00 PM local time) on 24 June 2007, eventually destroying 254 homes and burning 3100 acres. Images of the 3.9µm InfraRed (IR) and visible channels from GOES-12 (above; Java animation) and GOES-11 (below; Java animation) revealed a large “hot spot” (black pixels) associated with this fire, as well as a long smoke plume that spread quickly northeastward during the afternoon hours. Dark IR “hot spots” were first evident on GOES-12 imagery at 21:32 UTC and on GOES-11 imagery at 21:41 UTC, with a “processed fire” (red pixel) showing up on the GOES-11 Wildfire ABBA product at 22:00 UTC. Note that the hot fire saturated the 3.9µm detectors on GOES-12, causing the temperature to “roll over” and be falsely displayed as very cold (white) pixels. The saturation temperature of the GOES-11 3.9µm detectors (338.8º K / 66º C / 150º F) was reached as early as 22:30 UTC (2:30 PM local time).

The majority of the smoke was transported rapidly northeastward between Reno, Nevada (KRNO) and Fallon, Nevada (KNFL) by strong winds aloft; however, GOES-12 visible imagery indicated that some smoke at lower altitudes was curving southward away from the main plume and moving toward Fallon (and areas south of Fallon) after about 00:00 UTC on 25 June. The surface meteorogram from Fallon (below) indicates that surface visibility there dropped from 10 miles to 6 miles around 02 UTC as this smoke began to move into the area.

The fire continued to burn for several days; a Terra MODIS true color image from 26 June (below) shows a smaller smoke plume that was continuing to drift northward across the lake.

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The first documented F5 tornado damage on record in Canada occurred on 22 June 2007. GOES-12 10.7µm InfraRed channel imagery (above) and visible channel imagery (below) show the development of severe convection that spawned the tornado that struck the town of Elie in south-central Manitoba (just west of Winnipeg, station identifier CXWN) around 23:30 UTC. A subtle “enhanced-v” signature was seen on the GOES-12 IR imagery (with the most well-defined cold/warm cloud top temperature couplet of -62ºC/-51ºC appearing on the 00:15 UTC IR image); however, in this case the enhanced-v signature did not have the typical 20-30 minutes of “severe weather lead time” that is often noted with severe storms in the central US.

An alternate view of these severe thunderstorms is available using imagery from the GOES-11 satellite (below), which is positioned much father to the west (at 135º west longitude) than GOES-12 (at 75º west longitude). The well-defined cold/warm cloud top temperature couplet associated with the developing enhanced-v signature was evident on GOES-11 imagery a bit earlier in time (at 23:45 UTC).

An overpass of the NOAA-15 polar-orbiting satellite occurred around 22:31 UTC; a false-color image (using AVHRR channels 1, 2, and 3) shows a pair of convective towers that appear to be developing along a SW-NE oriented boundary just southeast of Lake Manitoba (below).

A closer view using the NOAA-15 AVHRR 10.8µm IR channel data (below) reveals cloud top temperature structures that resemble cold/warm couplets associated with those two developing storms just southeast of Lake Manitoba — however, the other NOAA-15 AVHRR visible and  IR channel images suggest that the cloud mass was probably “thinner” in those particular regions, allowing warmer radiation from below to bleed upward through the cloud and be sensed as warmer IR pixels.

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Severe thunderstorms developed over northwestern Kansas on 19 June 2007. An AWIPS image of the MODIS 11.0µm InfraRed (IR) channel (above) revealed an “enhanced-v” and a “warm trench” IR signature on adjacent storm tops. The coldest cloud top brightness temperature values were -77º C on both signatures; the warmest IR temperature associated with the “enhanced-v” was -58º C, while the warmest IR temperature in the “warm trench” was –61º C. 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).

A closer view of the MODIS IR image with a different color enhancement (above) shows that both IR signatures were surrounded by clusters of negative (yellow) and positive (red) cloud-to-ground (CG) lightning strikes. SPC storm reports listed hail (up to 1.75 inches in diameter) within 1 hour of the MODIS image in the region of both IR signatures, but only the southernmost enhanced-v storm produced a tornado; however, higher radar reflectivity values (65-70 dBz) were seen with the northernmost “warm trench” storm.

A comparison of the GOES-12 and MODIS IR images (above) demonstrates the better detection capability of these types of IR signatures using 1-km resolution MODIS IR imagery (vs 4-km resolution GOES IR imagery). The IR channels on the next-generation GOES-R Advanced Baseline Imager (ABI) will have a 2-km resolution.

GOES-12 10.7µm IR imagery (above; 100-image QuickTime animation) showed that these severe thunderstorms in Kansas persisted into the nighttime hours, and eventually became part of a very large Mesoscale Convective Complex (MCC) farther to the south over Oklahoma and Texas. Note the large number of IR pixels exhibiting brightness temperatures of -80º C or colder (violet enhancement) after 02:02 UTC; IR brightness temperatures were as cold as -93º C on a 23:22 UTC NOAA-12 AVHRR IR image, and as cold as -84º C on 05:10/05:13 UTC GOES / MODIS IR images (with 4159 negative and 334 positive CG lightning strikes at that time). Later SPC storm reports included hail up to 4.25 inches in diameter in Kansas (at around 00:05 UTC), and wind gusts to 94 mph in Texas (at around 07:09 UTC).

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