Fire near Lake Tahoe

June 25th, 2007 |

GOES-12 3.9µm IR + visible image

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).

GOES-11 3.9µm IR + visible image

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.

Fallon NV meteorogram

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.

Terra MODIS true color image

Elie, Manitoba tornado

June 22nd, 2007 |

GOES-12 10.7µm IR  images (Animated GIF)

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.

GOES-12 visible images (Animated GIF)

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).

GOES-11 10.7µm IR images (Animated GIF)

GOES-11 visible images (Animated GIF)

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).

NOAA-15 AVHRR false color image

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.

NOAA-15 AVHRR IR image

“Enhanced-V” and “Warm Trench” IR signatures

June 19th, 2007 |


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  image

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).

Severe Convection in Montana

June 16th, 2007 |

GOES-11 10.7µm IR image

Severe thunderstorms developed across parts of Montana on 16 June 2007, producing heavy rainfall (2-6 inches), large hail (up to 3 inches in diameter), damaging winds (gusting to 89 mph), and isolated tornadoes (SPC storm reports). GOES-11 10.7µm InfraRed (IR) imagery (above; Java animation) indicated cloud top brightness temperature values were as cold as -68º C (dark red enhancement) with these storms.

GOES-11 visible image

A closer view using GOES-11 visible channel imagery (above; Java animation) shows the storms in the Billings (KBIL) and Glasgow (KGGW) regions. Of particular interest was the northernmost Glasgow storm, whose northwest-to-southeast track deviated from that of the other eastward or northeastward-moving areas of convection over eastern Montana that day. Also note that the southernmost Billings storm exhibited a well-defined anvil plume after about 00:00 UTC on 17 June — this anvil plume was quite apparent in the visible imagery, but did not seem to exhibit much of a signal in the IR imagery (below).

GOES-11 visible + IR image

The large hail (driven by strong winds) from the northernmost Glasgow storm produced extensive damage to the wheat, alfalfa, and corn crops in that region — Tanja Fransen (WCM, NWS Glasgow) alerted us to the fact that the northwest-to-southeast oriented hail damage swath was clearly evident on Aqua MODIS true color imagery on 20 June, 4 days following the storm (below). A Java image fader applet allows a comparison between the MODIS images on 10 June (before the storm) and 20 June (after the storm), further highlighting hail damage swath. NWS Glasgow measured the damage swath to be about 285 miles long, and up to 12 miles wide (NWS public information statement).

Aqua MODIS true color image