AccuWeather predictive radar for 6 p.m., 12/15/21.
SIOUX FALLS, S.D. (KELO.com) — AccuWeather forecasters say a significant severe weather threat will unfold across parts of the Midwest from late Wednesday into Wednesday night. The dangers will include tornadoes, with the potential for some to touch down at nighttime.
The storms will generally target areas well north and west of those that were ravaged by a deadly and devastating tornado outbreak late last week, but there will be the risk for some severe thunderstorms and drenching rain to slow recovery efforts across portions of the Mississippi Valley that were pummeled by tornadoes.
Dozens of people have been killed, and officials fear the fatality count may continue to climb as search operations for those still unaccounted for continue.
Even though the setup for Wednesday night has significant differences when compared to last Friday night, especially for the geographical areas that will be targeted, there is a significant risk to lives and property. The most powerful storms could spawn tornadoes and damaging straight-line wind gusts up to 100 mph.
The Storm Prediction Center’s outlook for severe weather on Wednesday and Wednesday night calls for a moderate risk across parts of Wisconsin, Minnesota and Iowa. (SPC)
The storm system that will trigger the severe weather is as strong as last week’s system. It will unleash a tremendous amount of energy in the form of high winds, even where tornadoes do not touch down, over approximately half a million square miles of the Central states, stretching from the Rockies to the Upper Midwest.
“The storm may set low barometric pressure levels for December in parts of Minnesota Wednesday night, and that is a testament of the storm’s intensity,” AccuWeather Meteorologist Alex DaSilva said. Minneapolis could rival its record low pressure of 28.96 inches of mercury for December as the storm rolls through.
Moist air is needed to fuel severe thunderstorm and tornado development, and while this system will not pull in the same level of humidity that was present during last Friday’s outbreak, the central Plains and Upper Midwest will get an influx of humid air that is unusual for mid-December, according to DaSilva.
That anomaly, when combined with the tremendous wind energy from the storm, should be enough to spawn tornadoes toward evening Wednesday and during the first part of Wednesday night, resulting in the second nocturnal tornado threat in less than a week in December.
The main threat of a few tornadoes will begin late Wednesday afternoon Central time from near the border of northeastern Kansas to northwestern Missouri, eastern Nebraska and western Iowa. After dark, the tornado risk will shift northeastward across central and northwestern Iowa. The tornado threat may extend into part of southern Minnesota, where heavy snow fell from the same storm that brought the tornado outbreak last week. Tornado warnings have never been issued for Minnesota by the National Weather Service (NWS) in December.
A few hours after the initial thunderstorms capable of spawning tornadoes erupt, severe thunderstorms are likely to form a long line that will extend for hundreds of miles from Wisconsin, eastern Iowa and northern Illinois to southern Missouri and perhaps eastern Oklahoma. Fast movement of the storm system will allow this line to travel a great distance.
If wind damage from showers and thunderstorms occurs across a swath of more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length, then the event may be classified as a derecho, according to the NWS.
“It will definitely have derecho-like winds and forward speed, and it appears it will go the distance, so it would seem the criteria will be met,” AccuWeather Chief On-Air Meteorologist Bernie Rayno said. “Call it what you will, but the severe storms with high wind gusts will form a long, skinny line that will progress quickly to the south and east Wednesday night and into Thursday.”
Gusts in the storms, outside of any tornadoes, from Wednesday night to daybreak Thursday can frequent 50-80 mph, which is high enough to cause property damage, flip over trucks, topple trees and trigger power outages. In the most powerful supercell thunderstorms from Iowa to southeastern Minnesota, AccuWeather Local StormMax™ wind gusts up to 100 mph are possible and can lead to significant property damage.
Cities that are in the path of storms that may contain damaging wind gusts Wednesday night include Rochester, Minnesota; Des Moines and Davenport, Iowa; Madison, Milwaukee and Green Bay, Wisconsin; Chicago, Rockford and Peoria, Illinois; and St. Louis, Springfield and Kansas City, Missouri.
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Since the storm system and much of the wind energy with it will lift northward into Canada by Thursday, the forward speed of the front sparking severe thunderstorms is likely to slow down and weaken as it approaches the zone from southern Ohio to central Arkansas.
There is still the potential for heavy, gusty and isolated severe thunderstorms in this zone from Thursday to Thursday night. However, even though most of the storms will be subsevere by then, the mere effect of thunder and lightning along with gusty winds and downpours can have many people on edge that are just beginning to pick up the pieces from last Friday night’s tornadoes.
Another potential problem may arise due to the front’s forward speed slowing to a crawl.
“The setup from later Thursday to the first part of this weekend has the potential to bring repeating showers and thunderstorms or at least persistent rounds of drenching rain in some locations,” AccuWeather Senior Meteorologist Brett Anderson said.
A general 1-4 inches of rain will fall in the zone from northeastern Texas and much of Arkansas to southern Indiana and northern and western Kentucky, with an AccuWeather Local StormMax™ of 9 inches.
“The rain can be a major hindrance to operations in the wake of the devastating and deadly tornadoes that touched down in much of this same zone,” Anderson said, adding that enough rain could fall in some cases to lead to isolated flash flooding.
(By AccuWeather senior meteorologist, contributed this report.)
