MADISON, Wis. — Wednesday night’s severe weather outbreak in Wisconsin and parts of the Midwest was not only unusual in its timing for this time of year but also set records for its location and magnitude.
Severe thunderstorms developed Wednesday afternoon in eastern Nebraska. These storms formed into a squall line that raced northeastward at speeds that at times exceeded 80 miles per hour. The strong wind fields aloft coupled with high winds near the ground that swept spring-like warmth and moisture into the Midwest fueled severe thunderstorms and a number of tornadoes into Iowa, Minnesota, and Wisconsin by late Wednesday evening.
The National Weather Service Storm Prediction Center issued a severe weather outlook early on Wednesday morning that included a Moderate Risk (or level 4 on a scale of 1 to 5 in increasing severity) of severe thunderstorms over northern Iowa, southeastern Minnesota, and far west-central Wisconsin. A severe weather outbreak of this intensity and coverage has never been issued for an area this far north in the United States for this late in the year.
The prediction turned out to be very accurate. Here is an image of the severe weather reports overlayed onto the severe weather outlook from the National Weather Service.
As of early Thursday afternoon, almost 600 severe weather reports of tornadoes, high winds, and hail have been recorded at the Storm Prediction Center. These are preliminary reports; the number may change with time as duplicate reports are consolidated and additional reports are added to the list.
RELATED: National Weather Service confirms tornados in Neillsville, Lewiston
This list does not yet include an EF-2 intensity tornado already confirmed by the La Crosse National Weather Service office in Neillsville in Clark County. Also, the Twin Cities National Weather Service office is investigating damage reports of a tornado east of Eau Claire in the village of Stanley.
The tornado in Stanley may set a record for the northernmost tornado ever recorded in Wisconsin in December and possibly the northernmost December tornado ever in the United States. In any case, this is the latest a tornado has ever been reported in Wisconsin in December. Also, the La Crosse National Weather Service office confirmed an EF-0 tornado in Lewiston in Winona County, Minnesota. This is the first-ever December tornado reported in that state.
The tornado watch for Dane County and areas to the west was the first one ever for Wisconsin in December. The National Weather Service offices issued 71 tornadoes warnings from central Kansas and Nebraska northeastward into central Wisconsin. Every county was under a tornado or severe thunderstorm warning at some point Wednesday afternoon and evening in an area stretching from extreme northern Oklahoma to northeastern Wisconsin, and as far west as central Nebraska to as far east as Iowa County, just west of Dane County.
In addition to the tornadoes, very high straight-line winds were reported in many of the thunderstorms. So far, at least 60 reports of wind gusts of at least 75 miles per hour — or hurricane-force intensity — have been recorded. This is the most in a single day since 2004 when detailed wind reports began being recorded.
The Storm Prediction Center and the local National Weather Service offices will determine through weather records and storm damage surveys if this event qualifies as a derecho, a long-lived windstorm along a line of thunderstorms that produces damage over a path of at least 250 miles.
While Wednesday’s event meets that criteria, it is possible that some of the damage was caused more by straight-line winds ahead of or behind the storms rather than by the line of storms itself. These high winds continued to produce wind damage over much of the Midwest into early Thursday morning.
As additional information becomes available from the National Weather Service, local offices will post updated storm damage information.
Click below to visit each office’s website:
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