AWIPS images of the 4-km resolution GOES-12 10.7µm IR channel (above) showed that the land surfaces across the Upper Midwest region exhibited very cold brightness temperature values (darker blue enhancement) during the pre-dawn hours on 24 January 2008 — GOES IR brightness temperatures were as cold as -36ºC in northern Wisconsin, and -38ºC in northern Minnesota. Most of the area seen in the images above was cloud-free (except for the lake-effect cloud bands downwind of Lake Superior and Lake Michigan); the cloud-free surfaces could then be seen warming very quickly after sunrise. Much of the northcentral US had a deep snow cover of at least 5-10 inches, with snow depths of 15-30 inches common in northern Minnesota, Wisconsin, and Michigan; this deep snow cover (along with cloud-free skies and light winds) allowed for very strong radiational cooling of the air near the surface.

A higher-resolution (1-km) view using the MODIS 11.0µm IR channel and the MODIS fog/stratus product (below) revealed an amazing amount of structure in the surface brightness temperature field over the region (much of which was driven by terrain, with cold air drainage into low-lying areas such as river valleys); the coldest MODIS IR brightness temperatures sampled on the AWIPS images were -38ºC in northern Wisconsin and -42ºC in northern Minnesota. The MODIS fog/stratus product (created by computing the 11.0µm – 3.7µm brightness temperature difference) confirmed that there were no areas of fog or stratus cloud contributing to the interesting IR temperature structure seen across much of the Upper Midwest region around 08:20 UTC (2:20 AM local time). Note the appearance of “urban heat islands” (warmer IR temperatures, cyan enhancement) around cities such as Minneapolis, Minnesota and Sioux Falls, South Dakota.

NWS cooperative observer overnight minimum temperatures were as cold as -31ºF (-35ºC) at Sparta, Wisconsin and -39ºF (-39ºC) at Embarrass, Minnesota. There was also a reported minimum temperature of -51ºF (-46ºC) at a Minnesota Department of Transportation site northwest of Duluth (below), but the temperature data from that particular site appeared to be suspect.

Such cold temperatures aided in the formation of ice along the near-shore waters of western Lake Superior, as seen the following afternoon in a 250m-resolution MODIS true color image from the MODIS Today site (below). Lake Superior is the largest and deepest of the Great Lakes, and is usually the last to experience significant ice formation during the winter months.

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A Terra MODIS true color image from the SSEC MODIS Today site (above) revealed a swath of fresh snow cover across parts of Mississippi, Alabama, and Georgia on 20 January 2008. Snowfall amounts in the state of Alabama (which fell on the previous day) were as high as 5.8 inches near Verbena, 5.0 inches at Orrville, and 4.0 inches at Toxley (located on the MODIS imagery using Google Earth, below); snowfall up to 3.0 inches was reported in Mississippi, with 1.5 inches falling in Georgia.

AWIPS images of the MODIS visible channel, the 1.6µm “snow/ice channel”, and the Land Surface Temperature product (below) confirmed that this feature was indeed snow cover (snow is a strong absorber at the 1.6µm wavelength, and appears darker on the “snow/ice channel” image); in addition, the land surface temperatures within the area of snow cover were generally several degrees F colder (upper 20s to low 30s F, darker green enhancement) compared to the surrounding areas with bare ground (where land surface temperatures were generally in the mid 30s to around 40 F).

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The coldest arctic air of the 2007/2008 winter season (so far) settled in over the Great Lakes region on 19-20 January 2008. Most reporting stations in Wisconsin experienced a daytime maximum temperature below 0ºF on 19 January, with the coldest overnight minimum temperature on 20 January of -34ºF at Nekoosa in central Wisconsin. As this cold air streamed eastward across Lake Michigan, ice began to form along parts of the western and southern nearshore waters as seen on the MODIS true color image (above) from the SSEC MODIS Today site. Also note that the four larger lakes in the Madison area (located toward the upper left corner of the image) had all frozen solid again — they had all frozen completely by late December, but then the largest of Madison’s lakes (Lake Mendota) began to partially open during a brief warm period in early January 2008.

In a comparison of AWIPS images of the MODIS visible and 1.6µm “snow/ice channel” (below), the lake ice (and adjacent snow-covered land surfaces) exhibited a darker signal on the snow/ice image, in contrast to the brighter signal exhibited by the supercooled water droplet lake-effect snow cloud bands that covered much of the central and eastern portion of Lake Michigan.

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An animation of GOES-11 6.7 µm “water vapor channel” imagery (above) shows the development and intensification of a mid-latitude cyclone over the eastern North Pacific Ocean on 13 January 2008. Of particular interest in the water vapor imagery is the appearance of well-defined satellite signatures of an initial warm conveyor belt (WCB1), with a secondary warm conveyor belt (WCB2) later forming; a cold conveyor belt (CCB) is also seen emerging from beneath the secondary warm conveyor belt (as shown on the annotated image below). The “conveyor belt model” was developed and refined (most recently by authors such as Browning, Carlson, and Young) to help visualize the airflow through mid-latitude cyclones (schematic 1 | schematic 2); the flow is ascending in all 3 conveyor belts (producing the enhanced moisture and cloud signatures seen on the water vapor imagery), but the air rises to higher altitudes in the two warm conveyors than in the cold conveyor.

AWIPS images of the GOES-11 water vapor channel at 3-hour intervals (below) show that during the following 2-3 days this cyclone rapidly occluded, became quasi-stationary, and then eventually transitioned to a “cut-off low” which began to slowly retrograde to the northwest on 15-16 January.

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