December 1-7, 2009
Midwest Weekly Highlights - December 1-7, 2009
An Upside Down Start to December
There was a strong gradient in the temperature departures the first week of December, but not in the usual sense. The northern half of the region experienced above normal temperatures, while the southern half of the Midwest was much colder than normal. Average daily temperatures were 1°F to 3 °F above normal from western Minnesota eastward to lower Michigan. In the southern half of the region, temperatures were as much as 9°F below normal, with the greatest departures found from southwestern Missouri into the Ohio Valley (Figure 1). The week started out very mild, but quickly turned colder behind a strong storm departing the area. Only a few temperature records were set this week.
Significant precipitation was generally limited to the far northern and eastern portions of the region this week. Precipitation was two to four times normal across northern Minnesota and into the U. P. of Michigan. Precipitation was near normal to slightly above in a narrow band from the Missouri boot heel into southeastern lower Michigan, and in eastern Kentucky (Figure 2). Moderate to severe drought was still depicted over northern Wisconsin on the December 1 U.S. Drought Monitor.
One and Done
There was only one major weather system this week affecting the Midwest which brought the precipitation to the eastern half of the region. A strong low pressure system lifted northward from Gulf Coast on December 2 (Figure 3), moving the into the northern Appalachians by the morning of December 3 (Figure 4). This system spread rain into the Ohio Valley and brought rain to much of Kentucky and Ohio.
Snow in the far northern Midwest occurred early in the period as a weak storm system moved eastward from the Northern Plains into the Great Lakes. Three to five inches of snow fell across far northern Minnesota on December 1-2, and two to three inches fell in northern Michigan on December 3. As the Gulf Coast low moved into southern Canada on December 3 and 4, strong northwest winds produced 3 to 6 inches of snow along the eastern shores of Lake Michigan, with some isolated amounts to one foot in western lower Michigan. More than a foot of snow piled up over a three-day period in the Keweenaw Peninsula of Michigan. At the end of the week four or more inches of snow covered northern Minnesota, northern Wisconsin, parts of the Michigan U. P., and western lower Michigan (Figure 5).
The coldest air of the season so far spilled in behind the departing storm on December 5. Low temperature fell below zero in northern Minnesota, and were in the mid-teens as far south as southern Missouri and the Ohio River (Figure 6). The cold air was accompanied by some light snow and flurries as a weak disturbance aloft moved through the central Midwest.
The Next Storm Takes Aim
A variety of winter weather watches and advisories were posted for much of the northwestern half of the region on December 7 in anticipation of the next storm to take aim on the Midwest (Figure 7). On December 7 this storm was still west of the Rocky Mountains, but was expected to be affecting the region within 24 hours.
SDH