AWIPS MODIS water vapor channel imagery (above) shows a well-defined (but cloud-free) variant of a “Foehn gap” over central Colorado on 04 January 2007. This Foehn gap was oriented roughly north-south, just to the lee of the highest terrain of the Front Range of the Rocky Mountains (below), and formed as 60-70 knot winds at 500 hPa were flowing from west to east over that region (winds at Boulder CO KBJC were westerly at 21 gusting to 37 mph around the time of the MODIS image). A comparison of MODIS and GOES water vapor imagery reveals that, due to parallax error with the GOES-12 image, this Foehn gap incorrectly appears to the west of the highest terrain.  Also evident on the 1-km resolution MODIS water vapor image is a series of mountain waves further downwind of the Foehn gap (these mountain waves were not apparent on the 4-km resolution GOES-12 water vapor imagery). There was only one isolated pilot report of turbulence in the area around the time of the MODIS water vapor image, but air traffic is generally at a minimum during that time of day.

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An animation of 3-hourly water vapor image composites from AWIPS during the entire month of December 2006 (55-MB QuickTime animation; 1280×1024 screen resolution required) shows the diverse variety of storms that affected the northern hemisphere during that particular month. Strong winter storms left widespread swaths of heavy snow across much of the central US (01, 19-21, 29-31 December), created hurricane-force winds in the Pacific Northwest states (9-10 and 13-14 December), and deposited heavy lake-effect snowfall downwind of the Great Lakes (7-8 December). Outbreaks of severe convection that spawned tornadoes occurred in Pennsylvania (01 December), Florida (25 December), and Texas (29 December); a rare tornado was also reported near London, England (07 December). Super Typhoon Durian (01-05 December) and Typhoon Utor (06-13 December) made landfall in the Philippines and crossed into the South China Sea.

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A powerful winter storm produced widespread heavy snow and freezing rain across much of the central US during the 28–31 December 2006 period — total snowfall amounts included 58 inches in New Mexico, 44 inches in Colorado, 32 inches in Kansas, 16 inches in Nebraska and North Dakota, and 15 inches in South Dakota. Blizzard conditions created snow drifts up to 15 feet high in parts of the Plains. GOES-12 water vapor channel imagery from AWIPS (above | Java animation) revealed the large size of the storm as it was developing over the southern Rocky Mountains on 29 December. This storm also produced significant accumulation of ice due to freezing rain, which resulted in the loss of electrical power for tens of thousands of people in Nebraska alone; MODIS images from 31 December revealed two separate swaths of ice-covered ground in that state (from this storm and the previous winter storm earlier in the month).

In addition, this storm was responsible for an outbreak of tornadoes in Texas on 29 December (which produced 1 fatality) . GOES-12 10.7µm IR imagery (above | Java animation) showed the widespread convection that developed quickly over eastern Texas during the late morning hours — while numerous cloud top temperatures reached -60 C and colder (red enhancement), there were no enhanced-v signatures exhibited by any of these storms on the 15-minute GOES-12 images (nor on the 1-km resolution MODIS IR imagery); however, numerous cloud to ground lightning strikes were associated with this severe convection.

During the hours leading up to the development of the severe convection, AWIPS GOES sounder derived product imagery (above | Java animation) showed that a plume of total precipitable water having values of 30-45 mm (1.2-1.8 inches) was being advected north-northwestward across the Gulf of Mexico toward Texas.

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A comparison of GOES-12 and GOES-13 visible channel images (Java animation) centered over northeastern Minnesota on 25 December 2006 shows the improvement in navigation accuracy with the new GOES-13 satellite. Note how the surface features (such as frozen/snow-covered interior lakes, and the Lake Superior shoreline) appear to have significantly less image-to-image movement on GOES-13 versus GOES-12 — this is a result of changes to the GOES-13 spacecraft bus, which now has an improved Image Navigation and Registration (INR) system that uses star trackers to provide precision image navigation and registration information. This improved navigation will allow for better accuracy of satellite products such as satellite derived winds (or “atmospheric motion vectors”).
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Another item of interest which is apparent in these images is the fact that Duluth, Minnesota (KDLH) recorded it’s first Christmas Day with no snow on the ground since snowfall records began there in 1875. A MODIS true color image of Wisconsin confirms the lack of snow cover over the immediate Duluth vicinity and adjacent portions of northwestern Wisconsin — while some snow cover did exist to the north, west, and south of Duluth, even those areas generally had only 1-4 inches on the ground.

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