Fourmile Canyon fire near Boulder, Colorado

September 6th, 2010 |
GOES-13 3.9 µm shortwave IR images

GOES-13 3.9 µm shortwave IR images

A wildfire started in the Fourmile Canyon area northwest of Boulder, Colorado on the morning of 06 September 2010 — and strong winds (gusting to around 45 mph) in the wake of a cold frontal passage helped the fire to spread very quickly to a size of about 3500 acres. Some homes and buildings were destroyed, a few  evacuations were ordered, and there were a number of road closures in the area. AWIPS images of 4-km resolution GOES-13 3.9 µm shortwave IR data (above) showed the associated “hot spots” (black to red to yellow pixels) as the fire continued to grow during the day. Note the presence of very dry air over parts of the region –  the dew point was as low as -17º F at Boulder, due to downsloping winds.

AWIPS images of 1-km resolution MODIS 0.65 µm visible, MODIS 3.7 µm shortwave IR, and MODIS 11.0 µm IR channel data (below) showed a more detailed view of the fire smoke plume and hot spots at 18:13 UTC (12:13 pm local time).

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR images

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR images

The MODIS Land Surface Temperature (LST) product (below) indicated LST values as high as 126.7º F (red color enhancement) at the source region of the fire. Note how the Land Surface temperatures were reduced significantly beneath the thick smoke plume, due to a reduction in the amount of solar heating — LST values were in the mid 60s to low 70s F (darker green color enhancement) under the smoke plume, in contrast to areas with LST values in the low to mid 90s F (darker orange color enhancement) in adjacent areas. The highest elevations of the Rocky Mountains had LST values as cold as the low 40s F (darker blue color enhancement).

MODIS Land Surface Temperature product

MODIS Land Surface Temperature product

A comparison of the 1-km resolution MODIS Normalized Difference Vegetation Index (NDVI) product on 05 September (the day before the fire) and 06 September (below) indicated that the fire was burning in an area with adequate fuels — NDVI values near the fire source region were in the 0.5 to 0.6 range on 05 September.

MODIS Normailzed Difference Vegetation Index product

MODIS Normailzed Difference Vegetation Index product

250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed a very detailed view of the structure of the smoke plume.

MODIS true color Red/Green/Blue (RGB) images (displayed using Google Earth)

MODIS true color Red/Green/Blue (RGB) images (displayed using Google Earth)

By the end of the daylight hours, McIDAS images of GOES-13 0.63 µm visible channel data (below; also available as a QuickTime movie) indicated that strong winds aloft had blown the leading edge of the smoke plume as far northeastward as the Nebraska / Iowa border region. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) to monitor the landfall of Tropical Storm Hermine, so images were available as frequently as every 5-10 minutes.

GOES-13 0.63 µm visible images

GOES-13 0.63 µm visible images

Photo of the smoke plume

Photo of the smoke plume

The above iPhone image, looking northwest towards Boulder from the Davidson Mesa Open Space in Louisville, CO, was taken by Tom Davinroy about six hours after the fire started. There is also a time lapse video of the fire as it burned through the night.

===== 07 September Update =====

GOES-11 0.65 µm visible images

GOES-11 0.65 µm visible images

Due to a favorable forward scattering geometry, early morning GOES-11 visible images on 07 September 2010 (above) revealed that the smoke had been transported as far northeastward as southern Wisconsin, northern Illinois, and Lower Michigan.

A comparison of the 250-meter resolution MODIS true color RGB image on 06 September with the MODIS true color and false color RGB images on 07 September (below) showed that there was a much smaller, more localized smoke plume on 07 September — and the burn scar (which appeared darker brown in color) was apparent on the 07 September false color image. At the edge of the burn scar, the brighter pink area seen on the false color image was a heat signature of the active fire that was still burning at that time.

06 September MODIS true color and 07 September MODIS true color + false color images

06 September MODIS true color and 07 September MODIS true color + false color images

Heat burst in eastern Colorado and western Kansas

September 6th, 2010 |
MODIS 3.7 µm shortwave IR, 11.0 µm IR, and Land Surface Temperature product

MODIS 3.7 µm shortwave IR, 11.0 µm IR, and Land Surface Temperature product

As noted on the AccuWeather WeatherMatrix blog, some locations in far eastern Colorado and far western Kansas experienced a “heat burst” as dry convection passed across the region overnight. AWIPS images of the 04:35 UTC (10:35 pm local time) MODIS 3.7 µm shortwave IR, MODIS 11.0 µm IR, and MODIS Land Surface Temperature (LST) product (above) revealed the isolated pocket of warm temperatures (darker orange color enhancement: as high as 24º C / 75.2º F on the shortwave IR image, 21.5º C / 70.7º F on the IR image, and 25.4º C / 78.7º F on the LST product) just northwest of Burlington, Colorado (station identifier KITR), in the wake of the passing convection (which exhibited cloud top IR brightness temperatures as cold as -36º C, darker blue color enhancement). Around the time of the MODIS images, the surface air temperature at Burlington had abruptly risen to 89º F / 32º C with wind gusts to 53 knots (61 mph).

A comparison of the 1-km resolution MODIS 11.0 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm R image (below) demonstrated the dramatic improvement in feature detection with higher spatial resolution. Parallax error associated with the high viewing angle of the geostationary GOES-13 satellite was also obvious in the image comparison.

MODIS 11.0 µm IR  and GOES-13 10.7 µm IR images

MODIS 11.0 µm IR and GOES-13 10.7 µm IR images

An animation of the GOES-13 10.7 µm IR images (below) showed the warm heat burst signature (the pocket of darker orange colors) migrating eastward into western Kansas, where the surface air temperature at Goodland (station identifier KGLD) later rose to 92º F / 33º C at 06:00 UTC (Midnight local time). Note that there no cloud-to-ground lightning strikes associated with the convection that produced the heat burst.

GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

The heat burst signature was even evident on the 10-km resolution GOES-13 sounder Skin Temperature derived product image (below), with a maximum skin temperature value of 21.5º C / 70.7º F just to the northwest of Burlington, Colorado at 05:00 UTC (11:00 pm local time).

GOES-13 sounder Skin Temperature derived product image

GOES-13 sounder Skin Temperature derived product image

Another example of a heat burst signature on satellite imagery can be seen in this case at Amarillo, Texas in June 2002.