Midwest Weekly Highlights - October 25-31, 2010

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Historic Storm

The weather during the last week of October was dominated by a huge, historic storm. The system moved across the Midwest early in the week. The central pressure was among the lowest ever for a non-tropical storm in the continental US as the low tracked across northern Minnesota (Figure 1). The resulting pressure gradient caused strong, sustained winds that covered the region for two days, three days in the northern states. Severe weather (Figure 2), tornadoes and thunderstorm winds mostly, erupted along a trailing cold front that swept across the Midwest from west to east. Further to the north, wind damage was caused by non-thunderstorm winds reaching 60+ miles per hour.

State records for lowest sea level pressure were set in both Minnesota and Wisconsin. Some long-term weather stations also set their all-time record low pressure including Duluth and International Falls in Minnesota and Peoria and Springfield in Illinois. NWS offices across the region had stories on the storm and its impacts in their areas.
 

Precipitation

The big storm brought rain to most of the region. Nearly 300 daily precipitation records were set, mostly early in the week, as the storm moved through the Midwest. Northern Minnesota picked up two to nearly four inches of rain (Figure 3) which will allow for improvement of the drought conditions in the upcoming week (Figure 4). The trailing cold front extending all the way to the Gulf of Mexico causing rain and thunderstorms (Figure 5). Rainfall totals were above normal for the northern states and the southeast states. Below normal totals extended from southeast Michigan back to Missouri and Iowa with western Missouri and extreme southern Iowa getting less than 25% of normal (Figure 6).

Following the passage of the low, colder air and snow spilled into northern Minnesota. The first snow of the season brought two to six inches of snow to the northern reaches of the Midwest with some isolated reports of up to nine inches northwest of Duluth, Minnesota (Figure 7). There were also some daily records as a result of the snow.
 

Temperature Shift

As the low pressure moved through Iowa and Minnesota, most of the Midwest was experiencing strong warm advection on the southwesterly winds. Following the passage of the system winds shifted cutting off the warm advection and cooling down the region. A hard freeze reached down across Missouri on the morning of the 29th as minimum temperatures dropped into the 20s (Figure 8) following 50s (Figure 9) just a few days before. Daily temperature records were made up of mostly warm overnight minimums early in the week but a handful of cold records were recorded by the end of the week.

For the week, temperatures averaged out to above normal in the eastern half of the region, as much as 5° to 6°F above normal in eastern Michigan. Most of the western half of the region was near normal except Minnesota which recorded temperatures as much as 4°F below normal in the west central part of the state (Figure 10).
 

Several Midwest Tornadoes

October 26th was a busy day for tornadoes, especially considering how late it occurred in the year. Several tornadoes were reported across five states, all falling into the EF0 or EF1 rating on the Enhanced Fujita Scale.

In Illinois, five tornadoes were reported in the morning with the EF1 tornado near Elburn, Illinois (Kane County) causing the most damage as it destroying two barns and a grain bin. Wisconsin also reported a morning tornado on the 26th. The tornado that moved from Kenosha County to Racine County damaged trees, power poles, homes and injured two people. This brings the Wisconsin 2010 total to 44 tornadoes which ranks as the state's second highest count.

Indiana had tornado reports from 10 different counties on the morning of the 26th. Ohio had 14 reports spread across 11 counties . Across the two states, there was extensive damage to numerous buildings by more than 20 tornadoes.

Eight counties in Kentucky reported twisters, rated EF0 or EF1, with damage mostly to trees and some minor damage to homes and barns.
 

Strong Winds Cause Damage

High winds raked the Midwest with most of the reports from Missouri and Illinois on the first day and from Indiana, Kentucky, and Ohio on the following day. Widespread power outages were blamed on the high winds. Both thunderstorm and non-thunderstorm winds were strong enough to blow down trees along with power lines and poles. Hundreds of thousands of customers lost power all across the Midwest. In northeast Illinois, ComEd alone reported more than 300,000 affected customers. Semi-trucks were reported blown off interstate highways in both Iowa and Illinois. Wind and waves on the Great Lakes led to numerous warnings due to the dangerous conditions which included waves up to 30 feet on Lake Superior and Lake Michigan (Figure 11).
 

Minor Red River Flooding

Red River levels rose above flood level late in the week along the western border of Minnesota. Crests were projected to remain in the category of minor flooding as some locations had already crested by the end of the month.
 

Dry Halloween Weather

The kids trick-or-treating weather remained dry across the Midwest. Although temperatures were cool on the 31st, the dry conditions allowed for an enjoyable evening.
 

-MST-