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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Tornadoes are very rare in the state of Wisconsin during the month of January; however, severe convection did produce at least two tornadoes that moved across far southeastern Wisconsin during the afternoon hours on 07 January 2008. AWIPS images of the MODIS 11.0 µm IR and visible channels (above) depicted one of the early rounds of thunderstorms that produced several reports of hail around 17:00 UTC (11:00 AM local time). Note the unusually warm temperatures and high dew points that were surging northward behind a warm frontal boundary — new daily record maximum temperatures were set for 07 January at Milwaukee (63ºF; this was also Milwaukee’s warmest temperature on record for the entire month of January) and at Madison (50ºF). As this warm and moist air mass began to move over the deep snowpack (NOHRSC modeled snow depth) that was still in place on the previous day (06 January), new daily record high minimum temperature records were also set (39ºF at Milwaukee and 37ºF at Madison), and dense fog formed that afternoon which reduced visibilities to near zero and contributed to a series of chain-reaction accidents (involving around 100 vehicles) along Interstate 90 near Madison, Wisconsin.

AWIPS images of the GOES-12 10.7 µm IR channel (below) showed the evolution of the severe convection that produced the tornadoes in southeastern Wisconsin between about 21:45 UTC and 22:45 UTC. The corresponding radar imagery from NWS Milwaukee/Sullivan revealed a well-defined hook echo as the tornado moved across Kenosha county in extreme southeastern Wisconsin (producing EF-3 damage).

Prior to this event, only one January tornado had ever been recorded in the state of Wisconsin — a long-track F3 in Green and Rock counties on 24 January 1967.

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