MODIS true color images (viewed using Google Earth, above) showed that significant snow cover still remained over parts of the Upper Midwest region (especially across northeastern Ohio) on 11 March 2008. With the highway overlays removed, you can better see that several of the smaller towns across northeastern Ohio have a slightly darker appearance than the surrounding rural areas, due to the higher concentration of trees, buildings, and roadways in those urban areas. Also note the widespread ice that covered much of Lake Erie (in the upper right portion of the images), as well as along the southern shore of Lake Michigan (in the upper left portion of the images).

The National Operational Hydrologic Remote Sensing Center (NOHRSC) snow depth data (below) confirmed that many locations in eastern Ohio still had significant snow cover (as deep as 10-14 inches, with 4 inches on the ground at Toledo and 8 inches on the ground at Columbus) — however, not far to the west there was no snow on the ground in parts of Indiana (Indianapolis had zero snow depth, thus that area exhibited a light brown appearance on the MODIS true color imagery).

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An AWIPS image of the MODIS visible channel (above) showed the coverage of narrow ice features that were floating in the nearshore waters of southern Lake Michigan on 11 March (as was also pointed out by the National Weather Service forecast office at Milwaukee/Sullivan). Southwesterly winds at the surface were increasing during the day and gusting to 20-25 knots in some locations, allowing air temperatures to rise into the upper 30s to low 40s F over the snow-covered areas of southern Wisconsin and northern Illinois.

The effect of these gusty southwesterly winds on the offshore ice could be seen when comparing 2 consecutive MODIS true color images (viewed using Google Earth, below) — the time difference between the 2 images is about 101 minutes (the earlier Terra MODIS image time was around 17:11 UTC or 12:11 PM local time; the later Aqua MODIS image time was around 18:52 UTC or 1:52 PM local time), and the ice is seen to drift some distance to the northeast during that short time interval. The long, narrow, straight cloud features that also appear in the images are aircraft contrails.

[Image source: Liam Gumley, SSEC/CIMSS]

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A sequence of Terra and Aqua MODIS true color images from the SSEC MODIS Direct Broadcast site (above) reveal that widespread ice that had formed in parts of Lake Superior during the 08 March – 09 March – 10 March 2008 period. There are 2 images from each of those 3 days, with the Terra and Aqua images on each day separated by less than 2 hours — and even in that short time, you can see some movement of the ice features due to surface winds blowing across the lake and shifting the ice fields (plus the change in wind direction from day to day moved the ice features in different directions). Temperatures across northeastern Minnesota, northern Wisconsin, and the Upper Peninsula of Michigan had been fairly cold during the first week of March 2008, with minimum temperatures of -33º F (-36º C) at Embarrass, Minnesota and -26º F (-32º C) at Upson, Wisconsin on 07 March, and -31º F (-35º C) at Herman, Michigan on 08 March. While somewhat impressive, the ice coverage over Lake Superior did not match that seen back in February/March 2003.

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According to the National Snow and Ice Data Center, a large portion of the Wilkins Ice Shelf in the Antarctic (map) began to collapse during late February and early March 2008. A Terra MODIS visible image (above; courtesy of Shelley Knuth, SSEC Antarctic Meteorological Research Center) shows the extent of ice shelf disintegration on 10 March 2008.

The latest real-time IR satellite composite and Antarctic synoptic analysis chart from the SSEC AMRC is shown below.

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As a powerful winter storm intensified and produced heavy snowfall and blizzard conditions across much of the Ohio River Valley region of the US during the 07 March – 08 March 2008 period (Columbus, Ohio set new all-time records with a 20.4 inch storm total snowfall and 15.5 inches in 24 hours), a strong surge of cold air plunged southward across the Gulf of Mexico. This cold surge continued equatorward, crossed the terrain of southern Mexico, and emerged as a well-defined “Tehuano wind event“ over the Gulf of Tehuantepec along the Pacific coast (hence the name “Tehuantepecer“ given to this type of strong wind event). An AWIPS image of the GOES-12 10.7µm IR channel (above) includes plots of the surface frontal positions, the 850mb wind streamlines, and polar-orbiting microwave scatterometer winds from the QuikSCAT instrument on the morning of 08 March.

An AWIPS image of wind data from the QuikSCAT SeaWinds scatterometer instrument overlaid on the topography of the region (below) reveals the break in the higher terrain of the Sierra Madres mountain chain (known as the Chivela Pass), through which the northerly winds of a strong cold surge are able to pass from the Gulf of Mexico to the Pacific Ocean.

A closer view of the QuikSCAT wind data (below) shows that wind speeds at the 10-meter height were as strong as 46 knots (24 meters per second) as the cold “mountain gap winds” emerged over the Gulf of Tehuantepec. The accuracy of the QuikSCAT retrieved winds is probably very good in this case, since there is a very low rain contamination as noted by the Rain Falg value of only 6% (high rain contamination often leads to increased errors in QuikSCAT wind direction and speed magnitude).

An animation of GOES-12 visible images during the daylight hours on 07 March, followed by 3.9µm IR images during the overnight hours, and then visible images during the daylight hours on 08 March (below) shows the southward progression of a well-defined cloud arc (or “rope cloud”) that marked the leading edge of the cold surge.

A close-up animation of GOES-12 visible images (below) shows the period where the Tehuano wind event was moving through the Ixtepec, Mexico area (located just north of the Gulf of Tehuantepec) and flowing southward into the Gulf of Tehuantepec on 07 March. Note that the turbidity of the water in the small bay along the coast increased (as seen by the lighter gray, “muddy appearance” of the water).

The strong winds associated with a Tehuano wind event often cause upwelling of the coastal waters, which brings cooler and more nutrient-rich water to the surface. A comparison of MODIS true color and Land Surface Temperature images (below) from the MODIS Rapid Response System site indicated that a pool of colder offshore water temperatures (15º – 19º C, green to yellow colors) was in place in the Gulf of Tehuantepec, surrounded by warmer water temperatures in the 23º – 27º C range (orange colors). A closer view using 250-meter resolution MODIS true color imagery better shows the turbidity of the water in the bay just south of Ixtepec, as well as a plume of blowing dust being advected southward over the water.

Surface weather observations at Ixtepec, Mexico showed that winds changed to northerly and increased to 35 mph (16 meters per second) with the arrival of the Tehuano event (below). There was a ship report of winds as high as 50 knots (26 meters per second) over the Gulf of Tehuantepec at 18:00 UTC on 08 March; surface winds a day earlier were as high as 46 knots (24 meters per second) at Minatitlan, Mexico farther to the north (along the Gulf of Mexico coast).

Reference: Steenburgh, W. J., D. M. Schultz, B. A. Colle, 1998: The Structure and Evolution of Gap Outflow over the Gulf of Tehuantepec, Mexico. Monthly Weather Review: Vol. 126, pp. 2673-2691

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