This story may take weeks to be in final form. Any statistics reflect current understanding as of the date posted at the bottom.
A line of destructive thunderstorms tracked over south-central and southeastern Minnesota, as an extraordinary weather system produced severe thunderstorm hazards never before recorded during December in the state, along with other record-breaking and highly unusual weather phenomena.
These severe thunderstorms, with winds frequently exceeding 75 mph and occasional embedded tornadoes, traveled hundreds of miles from Nebraska and Kansas, through Iowa, southern Minnesota, and eventually into Wisconsin on Wednesday December 15th, 2021.
The storms entered southwestern Minnesota around 5:30 PM, and exited far southeastern Minnesota by 8:30PM. Moving at speeds of 65 to 80 mph, the storms damaged churches, barns, outbuildings, small businesses, and some homes. The winds uprooted and snapped trees, and blew down power lines as well.
The thunderstorms produced 22 confirmed tornadoes (as of Friday March 11, 2022) in Minnesota. The strongest hit the town of Hartland in Freeborn county, and was rated EF-2, with winds estimated at 115 mph. The National Weather Service confirmed over adozen additional EF-1 tornadoes, with winds of 90-110 mph, in Fillmore, Freeborn, Goodhue, Houston, Mower, Wabasha, and Winona counties. At least six EF-0 tornadoes with 80-85 mph winds were confirmed in Fillmore, Freeborn, Steele, and Winona counties, including one that went through Preston.
In addition to the tornadoes, the thunderstorms also produced damaging downburst winds (that is, unrelated to tornadoes), damaging Kasson, Austin, Rochester, and other towns in the southeastern part of the state. The Rochester airport recorded a wind gust of 77 mph at 7:45 PM, and the La Crosse National Weather Service received reports of gusts of up to 85 mph from personal weather sensors in southeastern Minnesota. A man was killed by non-tornadic winds in the Rochester area, when a tree fell on him.
(The National Weather Service may continue to add details about the severe weather reports in the weeks following the storm.)
This event was not only remarkable for occurring in December, but also for the fact that virtually all of the damage occurred after dark. Moreover, it also had an unusually large number hurricane-force wind gusts reported across the region. The NOAA Storm Prediction Center tweeted that this event produced more wind gust reports of at least 75 mph than any other event at any time of year, anywhere in the US, back to 2004, when consistent modern record-keeping began.
The long path length, the nearly-continuous nature of strong winds along that path, and the abundance of high-end and destructive wind gusts, appear to qualify this event as a "Derecho," (pronounced "deh-REY-cho"). Derechos are long-lasting, damaging windstorms caused by concentrated thunderstorms that travel long distances. They often produce pockets or swaths of tornado-like damage. This particular type of derecho is called a "serial derecho," forming from a "quasi-linear convective system", or QLCS. These are long lines or arcs of thunderstorms, with many cells producing damaging gusts as the complex races forward, typically ahead of a cold front.
If the system had only produced damaging thunderstorms and tornadoes, it would have been enough to qualify it as one of the most significant Minnesota weather events on record. However, when the final severe thunderstorms cleared southeastern Minnesota Wednesday evening, it marked the approximate half-way point on the timeline of damaging weather affecting the state. Indeed, a hand-off to a whole other wave of intense winds was taking place at about that time.
As the the severe thunderstorms raced away, a cold front plowed west-to-east across the state, ushering in a larger, longer-lasting, and equally intense rush of winds across much of southern Minnesota. These winds were not thunderstorm-related, but instead were the "pressure gradient winds" that equalize the pressure differences between the outer and inner parts of a low-pressure system. In this case, the low-pressure system was quite intense, and was able to generate an area of roaring winds about the size of Kansas. Arriving with bursts of rain, sleet, and snow, these winds eventually crossed the entire state, and produced gusts in excess of 60 mph across the southern third of Minnesota on and off for a period of five hours. The Redwood Falls airport recorded a gust to 78 mph, Jackson recorded a gust to 77 mph, and Fairmont recorded a 70 mph wind gust. These winds also led to damages scattered widely across rural Minnesota, and between the two separate high-wind events, the state experienced tens of thousands of power outages.
The strong gradient winds could have been associated with any similarly powerful low-pressure system, but the destructive thunderstorms were possible only because this low-pressure system was able to pull out-of-season warmth and humidity into the region. Temperatures reached well into the 60s F in southern and southeastern Minnesota, including 66 F at Caledonia and 65 F at Albert Lea and Preston. High temperature records were set at four of Minnesota's five major climate stations, including 64 F at Rochester, 58 F in the Twin Cities, 54 F in St. Cloud, and 49 F in Duluth. The Twin Cities recorded an hourly dew point reading of 54 F, breaking the record for the date, and marking the latest value of 50 F or higher on record. Previously no such values had been recorded between December 5th and February 20th.
The unseasonably muggy air was followed by a cold front that sent temperatures tumbling by 30-45 degrees in a matter of 12 hours in some areas. Back in the colder air, a blustery winter storm raged in western and northwestern Minnesota, with 2-5 inches of snow falling into winds gusting over 50 mph at times. Travel was nearly impossible in open areas late Wednesday night and early Thursday.
Forecasters had anticipated an extremely active weather day, and Minnesotans woke up Wednesday morning to find that the Storm Prediction Center had placed southeastern Minnesota in a "Moderate Risk" for severe thunderstorms, with the chance for wind gusts exceeding hurricane force and isolated strong tornadoes. Despite the tame-sounding name, Moderate Risks are actually quite rare and generally signify unusual severe weather damage potential. Minnesota typically sees this level of severe weather risk just once or twice per year on average, and has never had one issued during December; not even during November!
The Moderate Risk was followed by two Tornado Watches issued for southern Minnesota. No part of Minnesota had ever been in a Tornado Watch during December. The Tornado Watches were soon overrun by a flurry of Severe Thunderstorm and Tornado Warnings, and nothing even remotely like this had ever happened during any winter month.
The low-pressure system responsible for everything that happened was very strong, with pressure bottoming out near 975 millibars, but not nearly the strongest on record in Minnesota. The snows were also dangerous but somewhat typical. Nearly everything else, from the high temperatures and dew points, to the severe convective storms and tornadoes, to the destructive gales, was unprecedented, record-breaking, or unusual in some way.
Indeed, this mid-December destructive weather event will go down as one of the greats, and certainly as one of the most bizarre and oddly-timed episodes on record in Minnesota.
Below are some reports from National Weather Service forecast offices around the region. Note: these summaries may not be up-to-date and may be missing some details or known events.
PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 1136 AM CST FRI DEC 17 2021 ...NWS DAMAGE SURVEY FOR 12/15/21 FREEBORN COUNTY TORNADO EVENT... .OVERVIEW... HERE ARE THE PRELIMINARY DAMAGE SURVEY RESULTS FOR A SERIES OF THREE TORNADOES ACROSS RURAL FREEBORN IN SOUTHERN MINNESOTA WITH THE MOST SIGNIFICANT DAMAGE IN HARTLAND. .HARTLAND TORNADO... RATING: EF-2 ESTIMATED PEAK WIND: 115 MPH PATH LENGTH /STATUTE/: 2.17 MILES PATH WIDTH /MAXIMUM/: 55 YARDS FATALITIES: 0 INJURIES: 0 START DATE: DEC 15 2021 START TIME: 7:10 PM CST START LOCATION: 1 SW OF HARTLAND START LAT/LON: 43.7966 / -93.4943 END DATE: DEC 15 2021 END TIME: 7:13 PM CST END LOCATION: 2 NNE OF HARTLAND END LAT/LON: 43.8260 / -93.4751 SURVEY SUMMARY: A FAST MOVING TORNADO TOUCHED DOWN TO THE SOUTHWEST OF HARTLAND AND MOVED INTO TOWN DAMAGING NUMEROUS BUILDINGS, TREES, AND UTILITY POLES. THE DAMAGE IN THE SOUTHERN RESIDENTIAL PART OF TOWN WAS MAINLY TREE AND ROOF DAMAGE. AS THE TORNADO TRACKED INTO THE CENTER OF TOWN, MORE SIGNIFICANT DAMAGE WAS OBSERVED TO BUILDINGS ALONG BROADWAY STREET. THE MOST SIGNIFICANT DAMAGE WAS THE TWO BUILDINGS ALONG BROADWAY AND JOHNSON IN THE CENTER OF TOWN WITH SIGNIFICANT DAMAGE TO THE WALLS OF LOW RISE COMMERCIAL BUILDINGS. MORE TREE AND ROOF DAMAGE WAS OBSERVED TO THE NORTHEAST WITH SOME BRANCHES OBSERVED ALONG STATE HIGHWAY 13. THE TORNADO DISSIPATED TO THE NORTHEAST IN A FIELD WITH NO FURTHER DAMAGE OBSERVED. .ALDEN TORNADO 1... RATING: EF-1 ESTIMATED PEAK WIND: 105 MPH PATH LENGTH /STATUTE/: 3.62 MILES PATH WIDTH /MAXIMUM/: 90 YARDS FATALITIES: 0 INJURIES: 0 START DATE: DEC 15 2021 START TIME: 6:56 PM CST START LOCATION: 2 ENE OF WALTERS START LAT/LON: 43.6146 / -93.6292 END DATE: DEC 15 2021 END TIME: 6:59 PM CST END LOCATION: 1 SW OF ALDEN END LAT/LON: 43.6585 / -93.5880 SURVEY SUMMARY: FIRST DAMAGE OBSERVED OF TWISTED ROAD SIGN NEAR TORNADO ORIGIN POINT. PATH OF TREE AND UTILITY POLE DAMAGE CONTINUED TO THE NORTHEAST ENDING JUST SOUTH OF I-90. .ALDEN TORNADO 2... RATING: EF-1 ESTIMATED PEAK WIND: 100 MPH PATH LENGTH /STATUTE/: 1.64 MILES PATH WIDTH /MAXIMUM/: 40 YARDS FATALITIES: 0 INJURIES: 0 START DATE: DEC 15 2021 START TIME: 7:03 PM CST START LOCATION: 1 E OF ALDEN START LAT/LON: 43.6728 / -93.5438 END DATE: DEC 15 2021 END TIME: 7:05 PM CST END LOCATION: 3 ENE OF ALDEN END LAT/LON: 43.6932 / -93.5288 SURVEY SUMMARY: AFTER THE DISSIPATION OF THE PREVIOUS TORNADO, A NEW TORNADO DEVELOPED TO THE EAST OF ALDEN DAMAGING TREES AND A FARM OUTBUILDING. IT THEN CONTINUED TO THE NORTHEAST, DAMAGING ADDITIONAL TREES BEFORE DISSIPATING IN A FIELD. EF SCALE: THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES INTO THE FOLLOWING CATEGORIES. EF0...WEAK......65 TO 85 MPH EF1...WEAK......86 TO 110 MPH EF2...STRONG....111 TO 135 MPH EF3...STRONG....136 TO 165 MPH EF4...VIOLENT...166 TO 200MPH EF5...VIOLENT...>200MPH --- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 212 PM CST FRI DEC 17 2021 ...NWS DAMAGE SURVEY FOR 12/15/21 TORNADO EVENT - UPDATE 5... .UPDATE...ADDED TORNADO FROM PLAINVIEW MINNESOTA AREA .PLAINVIEW AREA TORNADO... RATING: EF1 ESTIMATED PEAK WIND: 93 MPH PATH LENGTH /STATUTE/: 4.584 MILES PATH WIDTH /MAXIMUM/: 40.0 YARDS FATALITIES: 0 INJURIES: 0 START DATE: 12/15/2021 START TIME: 08:02 PM CST START LOCATION: 3 SE PLAINVIEW / WABASHA COUNTY / MN START LAT/LON: 44.1313 / -92.1369 END DATE: 12/15/2021 END TIME: 08:05 PM CST END LOCATION: 4 ENE PLAINVIEW / WABASHA COUNTY / MN END LAT/LON: 44.1909 / -92.0967 SURVEY SUMMARY: A TORNADO PRODUCED DAMAGE TO NUMEROUS TREES AND SEVERAL FARM BUILDINGS SOUTHEAST TO NORTHEAST OF PLAINVIEW IN WABASHA COUNTY MINNESOTA. && EF SCALE: THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES INTO THE FOLLOWING CATEGORIES: EF0...WEAK......65 TO 85 MPH EF1...WEAK......86 TO 110 MPH EF2...STRONG....111 TO 135 MPH EF3...STRONG....136 TO 165 MPH EF4...VIOLENT...166 TO 200 MPH EF5...VIOLENT...>200 MPH NOTE: THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT AND PUBLICATION IN NWS STORM DATA. --- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 608 PM CST THU DEC 16 2021 ...NWS DAMAGE SURVEY FOR 12/15/21 TORNADO EVENT - UPDATE 2... .OVERVIEW...HERE IS A PRELIMINARY DAMAGE SURVEY RESULT FROM STORMS THAT HIT RURAL PARTS OF WINONA COUNTY, MINNESOTA DURING THE EVENING HOURS OF DECEMBER 15TH. OTHER SURVEY RESULTS ARE COMING. .WYATTVILLE TORNADO... RATING: EF-0 ESTIMATED PEAK WIND: 85 MPH PATH LENGTH /STATUTE/: 0.6 MILES PATH WIDTH /MAXIMUM/: 40 YARDS FATALITIES: 0 INJURIES: 0 START DATE: DEC 15 2021 START TIME: 8:09 PM CST START LOCATION: 1 MILE N OF WYATTVILLE MN START LAT/LON: 43.9605 / -91.7913 END DATE: DEC 15 2021 END TIME: 8:10 PM CST END LOCATION: 2 MILES N OF WYATTVILLE MN END LAT/LON: 43.9696 / -91.7892 SURVEY SUMMARY: DAMAGE WAS NOTED TO TREES, A GARAGE, AND SEVERAL OUTBUILDINGS ALONG AND NEAR COUNTY ROAD 23 BETWEEN LEWISTON AND WYATTVILLE. && EF SCALE: THE ENHANCED FUJITA SCALE CLASSIFIES TORNADOES INTO THE FOLLOWING CATEGORIES: EF0...WEAK......65 TO 85 MPH EF1...WEAK......86 TO 110 MPH EF2...STRONG....111 TO 135 MPH EF3...STRONG....136 TO 165 MPH EF4...VIOLENT...166 TO 200 MPH EF5...VIOLENT...>200 MPH --- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 546 AM CST THU DEC 16 2021 ..HIGHEST WIND REPORTS SINCE WEDNESDAY EVENING SOME REPORTS ARE FROM THUNDERSTORMS, BUT MOST ARE FROM NON-THUNDERSTORM WINDS OVERNIGHT. LOCATION SPEED TIME/DATE PROVIDER REDWOOD FALLS AP 78 MPH 1130 PM 12/15 ASOS FAIRMONT AP 70 MPH 1019 PM 12/15 AWOS EAU CLAIRE AP 67 MPH 0900 PM 12/15 ASOS ELLENDALE 5NNE 65 MPH 1050 PM 12/15 MNDOT EDEN PRAIRIE AP 63 MPH 0211 AM 12/16 ASOS CANNON FALLS 7SSE 63 MPH 0105 AM 12/16 MNDOT ST. JAMES AP 62 MPH 1155 PM 12/15 AWOS MANKATO AP 62 MPH 1107 PM 12/15 AWOS OWATONNA AP 62 MPH 1053 PM 12/15 AWOS TWIN LAKES 5SE 62 MPH 1110 PM 12/15 MNDOT MINNEAPOLIS-ST. PAUL AP 61 MPH 0317 AM 12/16 ASOS RED WING 4W 61 MPH 1235 AM 12/16 MNDOT WASECA AP 60 MPH 1135 PM 12/15 AWOS OLIVIA AP 60 MPH 1255 AM 12/16 AWOS NEW ULM AP 60 MPH 1135 PM 12/15 AWOS WASECA 1SSE 60 MPH 1130 PM 12/15 MNDOT RED WING 59 MPH 0206 AM 12/16 CWOP HANSKA 59 MPH 0700 PM 12/15 CWOP LYDIA 59 MPH 0116 AM 12/16 CWOP EAU CLAIRE 59 MPH 0108 AM 12/16 CWOP HUTCHINSON AP 59 MPH 1155 PM 12/15 AWOS NEW GERMANY 1NW 59 MPH 1220 AM 12/16 MNDOT GANOE HILL 59 MPH 0107 AM 12/16 RAWS HOPE 58 MPH 1109 PM 12/15 CWOP STANTON AP 58 MPH 1115 PM 12/15 AWOS MADELIA 3ENE 58 MPH 1150 PM 12/15 MNDOT MINNESOTA LAKE 57 MPH 1045 PM 12/15 CWOP SILVER LAKE 3E 57 MPH 1206 AM 12/16 MNDOT CLARA CITY 2WSW 57 MPH 1110 PM 12/15 MNDOT WINTHROP 2W 57 MPH 1140 PM 12/15 MNDOT MANKATO US-169 MILE POST 52 57 MPH 0100 AM 12/16 MNDOT EASTON 56 MPH 1046 PM 12/15 CWOP ALBERT LEA AP 56 MPH 1055 PM 12/15 AWOS WILLMAR AP 56 MPH 1215 AM 12/16 AWOS CRYSTAL AP 56 MPH 0436 AM 12/16 ASOS ST. PAUL DWTN AP 56 MPH 0200 AM 12/16 ASOS LITCHFIELD 3S 56 MPH 0211 AM 12/16 RAWS GLENCOE AP 55 MPH 1215 AM 12/16 AWOS --- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 841 PM CST WED DEC 15 2021 ..HIGHEST WIND REPORTS SO FAR TODAY [thunderstorm winds] LOCATION SPEED TIME/DATE ROCHESTER INTERNATIONAL AIRP 77 MPH 0745 PM 12/15 JCT CR 7 I-90 MILE POST 226 74 MPH 0800 PM 12/15 1 ENE DEXTER 73 MPH 0740 PM 12/15 2 E KASSON 72 MPH 0750 PM 12/15 3 N STEWARTVILLE 59 MPH 0750 PM 12/15 ROCHESTER 57 MPH 0756 PM 12/15 WABASHA 57 MPH 0828 PM 12/15 1 SSE KELLOGG 57 MPH 0820 PM 12/15 AUSTIN MUNICIPAL AIRPORT 54 MPH 0735 PM 12/15 --- PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 450 AM CST THU DEC 16 2021 ..HIGHEST NON-THUNDERSTORM WIND REPORTS FROM LAST 12 HOURS LOCATION SPEED TIME/DATE LAT/LON ..MINNESOTA ..DODGE COUNTY DODGE CENTER AIRPORT 58 MPH 0135 AM 12/16 44.02N/92.82W ..FILLMORE COUNTY PRESTON AIRPORT 60 MPH 1135 PM 12/15 43.68N/92.17W ..MOWER COUNTY AUSTIN MUNICIPAL AIRPORT 58 MPH 1115 PM 12/15 43.67N/92.92W ..OLMSTED COUNTY ROCHESTER INTERNATIONAL AIRP 77 MPH 1125 PM 12/15 43.90N/92.50W 3 N STEWARTVILLE 65 MPH 1205 AM 12/16 43.90N/92.48W MAYO HELIPAD 61 MPH 1115 PM 12/15 44.02N/92.48W ROCHESTER 48 MPH 1155 PM 12/15 44.05N/92.53W BYRON 45 MPH 0216 AM 12/16 44.04N/92.64W ..WABASHA COUNTY 1 SSE KELLOGG 63 MPH 1150 PM 12/15 44.28N/91.99W LAKE CITY 60 MPH 0145 AM 12/16 44.32N/92.44W ..WINONA COUNTY WINONA MUNICIPAL AIRPORT 52 MPH 1155 PM 12/15 44.07N/91.70W ---
Modified March 11, 2022