The lake-effect snowfall (LES) across the eastern Great Lakes region during the early February 2007 arctic outbreak has been phenomenal: as of 12 February, storm total snowfall amounts downwind of Lake Ontario have been as high as 141 inches in Redfield, New York (accumulations of 27 inches in 12 hours were reported, along with snowfall rates of up to 4-5 inches per hour). A series of daily Terra and Aqua MODIS true color images during the 03-09 February period (Java animation) show the well-defined LES bands over Lake Erie and Lake Ontario; you can also see the areal extent of lake ice increasing during this time over Lake Erie (this lake is the most shallow of the five Great Lakes, so it tends to freeze the earliest).

GOES-12 visible imagery (below; Java animation) shows the movement of an intense LES band across Lake Ontario on 06 February 2007.

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The strong arctic outbreak of early February 2007 brought an unusually cold and dry air mass over the northcentral and northeastern US. Water vapor channel imagery from the GOES imager and sounder on 05 February 2007 (above) showed a surprising result once the map overlay was removed (Java animation) — the outlines of parts of the Great Lakes and the Northeast coasts were clearly evident on the imagery. This is somewhat anomalous, given that the water vapor channel imagery normally depicts features in the middle to upper troposphere.

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GOES water vapor channel weighting functions calculated using rawinsonde data from Upton, New York at 00 UTC on 06 February 2007 (below) reveal that the GOES imager 6.5 µm water vapor channel (black plot) was detecting radiation from an atmospheric layer that peaked at an unusually low altitude (near 700 hPa), while the GOES sounder 7.4 µm water vapor channel (red plot) was detecting a significant amount of radiation from near the surface. This enabled a signal of the strong surface thermal contrast (very cold land surfaces adjacent to relatively warm bodies of water) to “bleed up” through what little water vapor was present in the atmospheric column, allowing us to see coastal outlines across the Great Lakes and Northeast US regions on the water vapor channel imagery.

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As a follow-up to the previous blog post, cold air and lake-effect snow continued across the Great Lakes region on 05 February 2007. GOES-12 visible imagery (above; Java animation) revealed a narrow filament of drift ice that was being pushed by strong winds eastward out of the northern portion of Green Bay (just north of Washington Island) and into Lake Michigan. An AWIPS image of the MODIS sea surface temperature (SST) product indicated that lake water temperatures had cooled to the 32º to 41º F (0º to +5º C) range off the coast of Wisconsin. Also, note how the motion of the lake-effect snow bands over Lake Superior (in northern portion of the images) changes during the day, as the boundary layer winds develop more of a westerly component. Finer detail in the drift ice structure in Green Bay and northern Lake Michigan can be seen on a 500-m resolution MODIS true color image (below); drift ice coverage was also increasing in southern Lake Michigan, from Milwaukee WI to Chicago IL to South Bend IN.

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The coldest air of the 2006-2007 winter season (surface temperatures on 04 February 2007 were as cold as -42º F / -41º C at Embarrass, Minnesota, -31º F / -35º C at Tomahawk, Wisconsin, and -21º F / -29º C at Randville, Michigan) was flowing over the still-warm waters of the Great Lakes (water temperatures were generally +35º to +41º F / +2º to +5º C), producing widespread bands of lake-effect snow (LES) which were very apparent on MODIS true color imagery (above). Note the transition from a multiple-LES-band regime over Lakes Superior and Michigan to more of a single-LES-band regime over Lakes Erie and Ontario (below). If you look closely, you can see that ice was beginning to form along portions of the northern shore of Lake Superior, as well as along the western shore of Lake Michigan and Lake Huron. The cold temperatures were limiting snow crystal growth (creating a fine, powdery snow), but snowfall accumulations still managed to reach amounts of 17 inches / 43 cm at Grandville in lower Michigan and 12 inches / 30 cm at Rainbow Lodge in the Upper Peninsula of Michigan; farther to the east, 18 inches / 46 cm fell at Boston in western New York. The strong winds were also producing wind chill temperatures in the -30º to -40º F / -34º to -40º C range across parts of Minnesota, Iowa, and Wisconsin.

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