November 22-30, 2010
Midwest Weekly Highlights - November 22-30, 2010
An Active End to November
The last nine days of November featured a range of weather from tornadoes to snow in the Midwest, in contrast to the first three weeks of generally quiet weather. Precipitation was the major story this period, as several inches of rain fell in the Ohio Valley putting a huge dent in the drought that has been occurring over the last three months.
There was a large range in average temperature departures the last nine days of the November. It was colder than normal across the upper Midwest, and warmer than normal in the southern third. Average daily temperatures ranged from 11°F below normal in northwestern Minnesota to 4°F above normal in southern Missouri (Figure 1). Temperatures were near to slightly above normal in northeastern lower Michigan and in northeastern Ohio. There were numerous high minimum and maximum temperature records set across the region on November 23-24 as strong southerly winds pumped in warm air ahead of a strong storm system.
Heavy Rain Puts Dent in Drought
Precipitation across the southeastern half of the region was from two to three times normal this period (Figure 2), with the heaviest rain in the Ohio Valley where Severe to Extreme drought has been occurring for the last few months. The abundant rainfall resulted in a one to two category improvement in drought status across the Ohio Valley (Figure 3). Only the Missouri Bootheel is still being depicted in Extreme Drought. Precipitation was also well above normal across the northern third of Minnesota and the Upper Peninsula of Michigan. In between these two areas, it was particularly dry from southwestern Minnesota south in northwestern Missouri. Precipitation in this area the last nine days of November was only 10 to 25 percent of normal.
November Tornadoes
This period began with a strong cold front bisecting the region (Figure 4). The temperature contrast between the air masses on either side of the front was more than 65°F. Early morning temperatures on November 22nd ranged from the upper 60s across southern Missouri to below 0°F in Montana and North Dakota (Figure 5). The contrast between the air masses combined with strong winds aloft set the stage for severe weather ahead of the front. To the north and west of the front moist air overrunning the very cold air set the stage for a variety of winter weather. On the morning of November 22nd a variety of winter weather advisories, watches, and warning were in effect for portions of Iowa, Wisconsin, and Minnesota (Figure 6). By early afternoon tornado watches were issued for portions of Missouri, Illinois, and Wisconsin as thunderstorms began to fire ahead of the front. The strongest storms occurred in northwestern Illinois into southern Wisconsin (Figure 7). In the late afternoon a tornado touched down in northern Illinois, causing damage and three injuries. The National Weather Service office in Chicago confirmed that an EF2 tornado occurred near Caledonia Illinois, northeast of the city of Rockford (Winnebago County). There was a a second confirmed tornado that also touched down in northern McHenry County. Two additional tornadoes touched down in Wisconsin as these storms moved northeastward out of Illinois. An EF1 tornado touched down in Kenosha County. A second EF1 tornado touched down just south of the Illinois-Wisconsin state line and moved into Walworth County.
While severe weather was generally confined to the mid to late afternoon, thunderstorms with heavy rain continued along the front as it pushed into the Ohio Valley. Rainfall for the 24 hour period ending on November 23rd was heaviest from central Missouri northeastward into lower Michigan, with many locations receiving an inch or more of rain (Figure 8). The front stalled out across the Tennessee Valley, then began to move north as a warm front on November 24th in response to another developing low pressure system in the Southern Plains (Figure 9). Thunderstorms developed north of the warm front's advance, and scattered severe storms were reported from southern Missouri into southern Indiana. Two tornadoes touched down in southwestern Missouri late on November 24th in Hickory and Polk Counties. In addition to the severe weather, flash flooding was reported from the heavy rain produced by training thunderstorms over the area. A wide band from near Springfield, MO (Greene County) to St. Louis and east-northeast through Illinois into western Indiana received from 2.50 to 3.50 inches of rain in the 24 hours ending the morning of November 25th (Figure 10).
The heavy rain shifted south into the Ohio Valley on November 25th, bringing copious rainfall to the heart of the drought in the Ohio Valley. During the period November 22-26 many locations from southeastern Missouri eastward through southern Illinois and Indiana received more than twice the amount of rain as they had received in the preceding two months (Figure 11). There were also 365 daily precipitation records set, and a number of locations set new November daily precipitation records.
Winter Weather Causes Travel Problem in Upper Midwest
As the cold air spilled in behind the advancing front rain changed to freezing rain and sleet of over northwestern Illinois and Iowa at the start of the busy Thanksgiving travel period. Multiple automobile accidents resulted from the icy conditions and there were some weather-related airport delays. To the north of the freezing rain, snow fell across the northern half of Minnesota, northern Wisconsin, and the Michigan Upper Peninsula. Three-day snowfall totals for this area reached upward of nine inches, with most locations receiving from four to eight inches (Figure 12).
Lake-effect snow occurred in northern Lower Michigan and the Michigan U. P. on November 26th. 24-hour snowfall totals on the morning of November 27th ranged generally from 3.0 inches to 6.0 inches (Figure 13), but a total of 9.0 inches was reported in Houghton, MI (Houghton County).
More Rain and Snow Ushers Out November
Another low pressure system was organizing over the Central Plains on the morning of November 29, spreading showers and some thunderstorms through Missouri (Figure 14). The shield of precipitation spread northeastward during the day bringing more rain to the eastern half of the region. During the afternoon the public reported an unconfirmed tornado in Livingston County, MO for the only severe weather report in the region that day. The axis of the heaviest rain extended from the Missouri Bootheel east northeast along the Ohio River into southern Indiana, where rainfall ranged from 1.50 to 2.00 inches. On the cold side of the system, a variety of winter weather watches and warnings were posted for Minnesota and northwestern Wisconsin (Figure 15). The watches and warnings continued through November 30th (Figure 16) as the low pressure system slowly northeast to Lake Superior (Figure 17). Snowfall amounts in Minnesota as of the morning of November 30th ranged from 4.0 to 8.0 inches (Figure 18), with 10.0 inches reported in both Morgan and Redwood Falls, MN (Redwood County). Snow continued to accumulate during the day in central and northeastern Minnesota, and 10 inches or more accumulated near Duluth (St. Louis County) (Figure 19). Storm total snowfall near Bruno, MN (Pine County) reached 13.5 inches by the morning of December 1st. Snow showers and flurries occurred as far south as the Ohio River through the night on November 30th as the colder air spilled into the central and eastern Midwest.
-SDH-