Midwest Weekly Highlights - November 17-23, 2008
Prelude to Winter
Persistent northwesterly flow funneled cold, dry air deep into the Midwest this week, keeping temperatures well below normal. In addition, the cold air flowing over the relatively warm waters of the Great Lakes generated lake-effect snow in Wisconsin, Michigan, Indiana, and Ohio.
Temperatures this week were well below normal across the entire Midwest, but departures exhibited a strong west-to-east gradient. Temperatures ranged from 5°F to 6°F below normal in the far northwestern portion of the region to 14°F to 16°F below normal in the southeast Midwest (Figure 1).
It was also very dry this week across the Midwest. Other than a few flurries and showers with cold frontal passages, there was no significant precipitation outside of the lake-effect snow belts (Figure 2). Snowfall was heavy in the lee of the lakes, with amounts for the week topping 24 inches at locations in the Michigan U. P. More than 12 inches of snow fell in lower Michigan, northern Indiana, and northeastern Ohio (Figure 3). At the end of the week snow depths exceeded 14 to 16 inches in the Michigan U. P. (Figure 4). There was little change in the U.S. Drought Monitor this week. Areas of Severe Drought continue to be depicted in Wisconsin, the Michigan U. P., and in Kentucky, while a portion of south-central Kentucky was depicted in Extreme Drought (Figure 5).
Lake-Effect Snow Machine Into High Gear
On November 17 an Arctic air mass was building into the Midwest (Figure 6). Strong northerly winds circulating around the high pressure system picked up moisture off of the Great Lakes, producing bands of localized heavy snow across parts of four states. A variety of winter weather watches, warnings, and advisories were posted for areas downwind of the lakes (Figure 7). Snow began late on November 17 and continued through November 18. Amounts in Michigan exceeded 14 inches in Marquette County and 10 inches in Allegan County. Snow abated late on November 18 as the high moved east and winds shifted into the south over the Midwest. However, another cold front was already moving out of the Northern Plains, setting the stage for another round of snow on November 20. Watches, warnings and advisories were again issued for areas downwind of the lakes as some of the coldest air of the season so far spread across the Midwest (Figure 8). High temperatures on November 20 in northern Minnesota were only in the low and mid teens. Gaylord, MI set a new record low temperature of -2°F on the morning of November 21, breaking the old record of 1°F set in 1987. Bands of snow developed as the frigid air streamed over the comparatively warm waters of the lakes (Figure 9). Eight to 12 inches of snow fell in southern Michigan and northern Indiana, while 4 to 7 inches of snow accumulated in northern Ohio. An inch of snow also accumulated in western and southern Ohio, and more than 2 to 3 inches fell in higher elevations in eastern Kentucky (Figure 10).
The lake-effect snow continued into November 21, but then tapered off as the center of the high moved to the east coast and another system poised to push through the Midwest. Some light snow developed across western and central Iowa in advance of this system on November 22, with 1 to 2 inch amounts in general, but some locally higher amounts of 4 to 5 inches.