Midwest Weekly Highlights - November 22-30, 2005

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An Active End to a Turbulent November

The period of November 22-30 had cold and warm, snowy and rainy, and calm and violent weather interludes. A few areas, including western Minnesota, the lake effect belts of Michigan, and southeastern Missouri / southwestern Illinois, received more then 1.5 inches of precipitation for the nine days (Figure 1). Precipitation amounts were 200-700% of normal in the northern Midwest, but there were some drier than normal patches in the southern portion of the region in areas of developing drought (Figure 2). Despite the cold start to the period, the warm influx was of such a large magnitude at mid-period that Minnesota, Iowa, and Missouri were actually above normal in temperature for the whole 9 days, while the eastern Midwest was only 2-4°F below normal (Figure 3). Significant lake effect snows are apparent in the snow fall map for the period (Figure 4), along with the heavy snow in western Minnesota from the huge Great Plains blizzard on the 27th and 28th. Despite the adequate moisture that fell on the core drought region from November 22-30, low precipitation records were set for the March-November period in 2005 at both Chicago and Rockford. Therefore, the underlying hydrologic drought remains extreme in far eastern Iowa and northern Illinois (Figure 5, National Drought Mitigation Center). However, this November will be most remembered for 4 widespread and highly destructive severe weather events in the Midwest, all of which led to at least one fatality, including an event on the 27th.
  

Low Pressure Systems and Snow

Early in the period, a strong low pressure center moved across the far northern Midwest. By late on the 23rd, sea level pressure was below 986 mb in the Lake Superior area (Figure 6, College of DuPage - COD), and strong trough and cold front swept through the region with moderate to heavy snow before it (Figure 7, COD), and high winds behind it (Figure 8, COD). In addition to this snow, strong lake effect events took place downwind of the still-warm Great lakes (Figure 9, University Corporation for Atmospheric Research - UCAR). Between the original storm, enhanced lake effect snow on the 24th, and another clipper system on the 25th, snow totals reached more than a foot in the Upper Peninsula of Michigan, western lower Michigan, and northeastern Ohio (Figure 10). Cold and snowy conditions greatly impeded road travel for the Thanksgiving holiday, especially in Michigan and northern Indiana and Ohio. In a sad outcome of the cold weather, the initial freezing of ponds and lakes tempted some people to walk or skate on the ice, and three people broke through the ice and drowned in two separate incidents in Wisconsin.
  

The Last, Last Severe Outbreak of the Season

On November 27, a tremendous surge of warm (Figure 11a, Unisys) and moist (Figure 11b, Unisys) air entered the Midwest ahead of a strong low pressure system in Kansas (Figure 11c, Unisys). Along with this warm, unstable air, a very strong jet stream moved in overhead (Figure 12, Unisys). Considerable rain fell ahead of the warm front in Wisconsin and Michigan (Figure 13, UCAR). While the Great Plains states were being warned for blizzard conditions on the backside of the low, the western Midwest was being watched for tornadoes (Figure 14, Storm Prediction Center - SPC). Some of this nasty winter portion of the storm impacted western and northern Minnesota. In far western Minnesota, the full force of the blizzard whipped 4-8 inches of snow into drifts several feet high in places, causing white-out conditions and closing roads. More than 100 cars went off the road due to bad conditions in western Minnesota prior to road closure, either from the snow itself or a layer of freezing rain preceding the snow. One road fatality was attributed to the storm in Minnesota.

There were severe impacts in the Midwest related to wind, hail, and tornadoes to the south and east of the storm center. Two lines of storms developed ahead of cold front through Missouri and Arkansas (Figure 15a, SPC), leading to a number of tornado and severe thunderstorm warnings early during the evening of the 27th (Figure 15b, SPC). Most of the energy eventually went into a single squall line that entered Illinois and Kentucky early in the morning of the 28th (Figure 16a, SPC), resulting in a large number of severe thunderstorm warnings (Figure 16b, SPC) before fading later in the morning. More than 30 tornado touch downs were reported in the south central U.S., including 8 in Missouri, and several dozen severe wind and hail events were reported in Iowa, Missouri, and Illinois (Figure 17, SPC). One person near the town of Briar in southeast Missouri lost their life when a tornado destroyed their home.

The period ended just as a strong clipper system entered the far western Midwest on the evening of the 30th. Considerable snow ensued overnight (Figure 18, UCAR), causing substantial travel delays and other impacts. The snow from this storm will be recorded by most stations on the morning of December 1.