GOES-12 6.5 µm water vapor images

AWIPS images of the 4-km resolution GOES-12 6.5 µm water vapor channel (above) showed a southward-propagating  lee-side cold frontal gravity wave over New Mexico and Texas on 22 October 2008. This gravity wave was caused by a surface-based cold frontal boundary that was moving southward across the region.

MODIS 6.7 µm water vapor image + fog/stratus product image

A comparison of the 1-km resolution MODIS 6.7 µm water vapor channel and the MODIS fog/stratus product (above) indicated that there were narrow cloud bands along the leading edge of the frontal boundary / gravity wave, as well as more extensive patches of fog and/or stratus behind the front in the Texas panhandle.The MODIS Land Surface Temperature (LST) product (below) depicted LST values dropping into the 40s F (green colors) behind the front, with much warmer LST values in the 50s and 60s F (yellow to orange colors) ahead of the front.

MODIS 6.7 µm water vapor channel + Land Surface Temperature product

NOAA wind profiler data from Jayton, Texas (below) showed the deepening of the cold northerly flow after the cold front moved through the area — the top of the cold air appeared to be close to the 700 hPa level (around 10,000 feet above ground level).

Jayton, Texas NOAA wind profiler data

GOES-12 water vapor channel weighting functions calculated for the rawinsonde profiles at Amarillo, Texas (below) demonstrated a significant lowering of the layer being detected by the water vapor channel in the 12 hours between 00 and 12 UTC on 22 October. With the drier air mass in place at 12 UTC, the GOES-12 water vapor channel was able to detect a substantial amount of energy originating from within the 500-700 hPa layer, allowing the signature of the frontal gravity wave to appear on the GOES-12 water vapor imagery. The wave structure was better-defined on the MODIS water vapor image, due to the improved spatial resolution and the more direct satellite viewing angle.

GOES-12 water vapor channel weighting functions for Amarillo TX

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GOES-12 10.7 µm IR images

AWIPS images of the GOES-12 10.7 µm “IR window” channel (above) showed extensive cloudiness associated with a shortwave trough that was moving eastward across the Upper Midwest region during the morning hours on 17 October 2008. IR cloud top brightness temperatures of -20º to -40º C (blue to green colors) corresponded to areas of light precipitation (radar mosaic). Also shown on the IR imagery were  aircraft Icing AIRMET advisories (outlined in red) that were issued at 09:00 UTC and 14:00 UTC –  the 14:00 UTC AIRMET was forecasting moderate icing between the freezing level (which was between 5,000 and 10,000 feet) and 20,000 feet. In fact, there were a number of aircraft pilot reports of icing (plotted in yellow) within the boundaries of these Icing AIRMETs.

A closer view using AWIPS images of the MODIS visible channel, 11.0 µm “IR window” channel, Cloud Top Temperature (CTT) product, and Cloud Phase product at 17:29 UTC (below) indicated that much of the cloud shield along the trailing (western) edge of the shortwave over Minnesota and Iowa exhibited cloud top temperatures that were below freezing (generally in the -5 to -12º C range), but the MODIS Cloud Phase product designated those trailing edge clouds as “Water droplet” clouds (blue enhancement). Within this area of supercooled water droplet clouds were several pilot reports of icing at the 8000-foot altitude  across southern Minnesota and western/central Iowa.

MODIS visible + IR window + Cloud Top Temperature + Cloud Phase

A comparison of AWIPS images of the MODIS Cloud Phase product and the GOES-12 sounder Cloud Top Height product (below) showed that these pilot reports of icing at the 8000 foot level were well below the tops of the clouds, which were generally in the 13,000-15,000 foot range (green colors on the Cloud Top Height product).

MODIS Cloud Phase product + GOES-12 sounder Cloud Top Height product

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GOES-11 + GOES-12 water vapor channel images

AWIPS images of the GOES-11 + GOES-12 water vapor channels (above) showed the large size of a major snowstorm that impacted much of the western US during the 10 October – 12 October 2008 time frame. This storm dropped as much as 48.8 inches of snow at Cole Creek, Montana and 29.7 inches at Lander, Wyoming (their greatest October snowfall on record), and Glasgow, Montana received 12.8 inches of snow on 12 October (their heaviest snowfall for any calendar day during the month of October). At Billings, Montana the snow depth of 9 inches on 13 October was the earliest date on record for a 9-inch snow depth.

AWIPS images of the MODIS visible channel and the 1.6 µm near-IR “snow/ice” channel (below) displayed the areal coverage of snow on the ground across much of Wyoming, eastern Montana, far northwestern South Dakota (including the higher elevations of the Black Hills) and western North Dakota, stretching northeastward into portions of Saskatchewan and Manitoba on 13 October. Snow cover exhibits a darker signal on snow/ice channel imagery (in contrast to supercooled water droplet clouds, which appear as lighter shades of gray).

MODIS visible and snow/ice channel images

An AWIPS image of the MODIS Land Surface Temperature (LST) product (below) showed the effect of the deep snow cover on surface temperatures across much of Wyoming and Montana on 13 October — LST values within the snow swath were only in the upper 20s to low 30s F (green colors), compared to the 60s and 70s F (orange colors) north of the deep snow cover. The daily maximum temperature on 13 October at Glasgow, Montana was only 37º F (which tied the record for coldest maximum temperature for that date), while the daily high temperature of 28º F at Wisdom, Montana was the earliest date for such a cold maximum temperature.

MODIS Land Surface Temperature product

A 250-meter resolution MODIS true color image (below, viewed using Google Earth) displayed the extent of the snow cover across parts of Wyoming and Montana. Note that there were a few snow-free patches located within the broad swath of snow cover (a result of the complex terrain across the region).

MODIS true color image (viewed using Google Earth)

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GOES-11, GOES-12, GOES-13 water vapor images

Strong southwesterly winds over the southern and central Rocky Mountains led to the development of mountain waves downwind of the higher terrain in Colorado and New Mexico on 10 October 2008. A distinct mountain wave signature was seen on 6.7 µm water vapor channel imagery from GOES-11 and 6.5 µm water vapor channel imagery from GOES-13 and GOES-12 (above). Note the improved appearance of the mountain waves on the 4-km resolution GOES-13 and GOES-12 imagery (compared to the 8-km resolution GOES-11 imagery). These mountain waves were also easier to identify and track using GOES-13, due to the more direct viewing angle of GOES-13 (positioned at 105º W longitude) and also the fact that GOES-13 was able to operate and supply imagery through the eclipse period (when the satellite was in the Earth’s shadow, and the solar panels could not supply power to the spacecraft).

AWIPS images of GOES-12 and MODIS water vapor channel data

AWIPS images of the GOES-12 and MODIS water vapor channel data (above) showed further improvement in mountain wave identification using 1-km resolution data from MODIS. Mountain waves on water vapor imagery have long been recognized as a signature of potential clear air turbulence, and there were indeed a few pilot reports of light to moderate turbulence over eastern Colorado and New Mexico (below).

AWIPS image of GOES-12 water vapor channel data + pilot reports

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