Midwest Weekly Highlights - December 1-7, 2004

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The first week of meteorological winter was mild and wet across most of the Midwest.  The warmest weather was found over the northwestern portion of the region, where temperatures were 8F to 10F above normal from western Minnesota to northwestern Iowa (Figure 1).  A broad area of temperatures 4F to 6F above normal extended from Iowa and Wisconsin across Illinois and into Ohio. 

A series of low pressure systems moving through the Mississippi and Ohio River valleys during the week brought copious amounts of precipitation to the southeastern two-thirds of the Midwest (Figure 2).  Precipitation was two to three times normal for the week, and some locations in the central Midwest received more than half the normal December precipitation in the first week.  While precipitation across much of the southern half of the region was mostly rain this week, significant snow fell across the northern Midwest as well as in a band from northern Missouri to northeastern Illinois (Figure 3). The southern half of Minnesota and northern Iowa missed out on much of the precipitation, with only 10 to 50 percent of the normal weekly amount. 


The Storm Train

This first of several low pressure systems this week began to affect the region on November 30th, and by dawn on December 1st it was already exiting the region (Figure 4, Unisys).  However, in its wake the storm and cold front left a band of snow from northern Missouri through northeastern Illinois and into Michgan.  Rain changed to snow behind the cold front late on November 30th and into the early morning hours of December 1.  For more description on the impacts of this storm, see the November 30 summary of the Midwest Climate Watch.

High pressure and seasonable temperatures made for pleasant weather across the central and southern Midwest December 2-4.  To the north, winter weather hung on as a front stalled out over the upper Great Lakes (Figure 5, Unisys).  A low pressure wave on the front brought snow to northern Wisconsin and Michigan, prompting heavy snow warnings for parts of northern Michigan.  The cold front finally pushed through the upper Midwest on December 4, only to stall across the central Midwest on December 5th.  Yet another low developed on the front in the central plains and moved toward the central Midwest on December 6-7.  Precipitation with this sytem was mostly rain, and lots of it.  A broad swath from southern Missouri through Illinois and into southern Michigan received an inch or more of rain (Figure 6).  Flood watches were issued for much of southwestern Missouri as the heavy rains with this system fell on saturated ground, and a number of smaller rivers and streams experienced minor flooding in Missouri, central Illinois, and Indiana.