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Unique Storm of December 15, 2021

Unique Storm of December 15, 2021:

The storm system that crossed over Nebraska, Iowa, Minnesota, Wisconsin and Illinois over December 15-16 was almost totally unique in many of its atmospheric attributes. Hundreds of temperature and dew point records were set with the rapid transport of heat and moisture from the south. The wind structure of the atmospheric layers supported record-setting wind speeds, as well as producing 25 reports of tornadoes (12 in NE, 13 in IA), and three suspected reports of tornadoes in MN, yet to be verified. Though fast moving, the storm system produced some record-setting rainfall amounts as well.

Among the most rare and unique measurements of the storm were: confirmed tornadoes on the ground near Lewiston (Winona County) and Hartland (Freeborn County), the first ever observed such storms in Minnesota during the month of December; a radiosonde (balloon) measured precipitable water measurement from the Twin Cities (integrated water vapor content in the atmosphere overhead) of 1.23inches, the highest measurement ever made in Minnesota during the months of December, January, and February; a dew point measurement at MSP airport of 55°F, the highest historical dew point measurement historical for the Twin Cities between December 6th and March 6th; a maximum temperature reading of 66°F at Caledonia, Winona, and Austin, all-time statewide record high for this time of year, and about 30-35 degrees F above normal.

A sampling of records set during the storm across Minnesota (for long term climate stations):

New record daily high temperatures:
65°F at Albert Lea
64°F Rochester, Grand Meadow, and Theilman
63°F at Winnebago and La Crescent
62°F Mankato
61°F at Jordan
60°F at Red Wing
58°F at MSP
55°F at St Cloud
54°F at Mora and Litchfield
49°F at Duluth

A sampling of the rainfall records from the storm across Minnesota (long term climate stations):
2.14” at Embarrass
2.10” at Zumbrota
1.96” at Floodwood
1.77” at Brainerd
1.44” at Hibbing
1.34” at Alexandria
1.28” at Tower
1.25” at Long Prairie
1.16” at Dawson
1.03” at Canby

Sampling of some record-setting maximum wind gusts:
85mph at Plainview
84 mph at Mabel and Harmony
83 mph at Grand Meadow
78 mph at Rochester Airport and Redwood Falls Airport
75 mph at Morristown
72 mph at Kasson
70 mph at Dodge Center
68 mph at Elko New Market

Sampling of record dew points:
55°F at MSP
59°F at Winona
57°F at Austin and Faribault
56°F at Preston

Overall, the convergence of these atmospheric conditions over Minnesota at this time of year is probably a “singularity” or one-off in historical terms. It can certainly be argued that it is symptomatically characteristic of climate change and will probably be investigated and reported by the American Meteorological Society specialists that do “forensic meteorology” studies. 

Weekly Weather Potpourri:

Preliminary data indicate that the year 2021 will end up among the warmest six years in Minnesota history (back to 1895) on a statewide basis. In addition, though it will be noted as a year when drought had a major effect on the state (especially in summer), the year 2021 will likely be about the 30th driest year in state history, and far wetter than some of the worst drought years such as 1910, 1976, 1936, 1934, and 1917.

This week’s AGU-EOS Bulletin highlights some recent tornado research out of the University of Oklahoma. The findings suggest that tornado frequency in the May through September period across the Southern Plains and Midwest may decline, but that the intensity of storms may increase. In addition, the study suggests that during the cool season, tornadoes may actually increase in both frequency and intensity.

NOAA released its annual Arctic Climate Report Card this week, assessing how the warming climate trends are affecting the high latitudes of the Northern Hemisphere. It is a telling tale of decline in sea ice volume, disappearance of permafrost, browning of the tundra, and record-setting warmth.

Super Typhoon Rai lashed the Philippines with high seas, damaging winds, and very heavy rains this week as it crossed over into the South China Sea. The BBC reported thousands of people were evacuated to higher ground and there were widespread power outages.

MPR listener question:

Besides the storm on December 15th this week have we ever experienced a seasonal storm that was completely out of character and not in our range of historical experience in Minnesota?


In my experience the only other storm that I would characterize as a historical singularity is the March 31, 2014 storm that passed over southwestern Minnesota, notably the counties of Lincoln, Lyon, Yellow Medicine and Lac Qui Parle. This storm produced a simultaneous blizzard and tornado warning for citizens of the area between 4pm and 5pm in the afternoon. If you were driving north that day on Hwy 75 you could have seen both of these storm types within miles of each other. This is perhaps one of the oddest weather events in state history.

Twin Cities Almanac for December 17th:

The average MSP high temperature for this date is 28 degrees F (plus or minus 12 degrees F standard deviation), while the average low is 15 degrees F (plus or minus 14 degrees F standard deviation).

MSP Local Records for December 17th:

MSP records for this date: highest daily maximum temperature of 53 degrees F in 1939; lowest daily maximum temperature of -5 degrees F in 1945; lowest daily minimum temperature of -17 degrees F in 1985; highest daily minimum temperature of 35 degrees F in 1977; record precipitation of 0.81 inches in 1908. Record snowfall is 10.8 inches also in 1908.

Average dew point for December 17th is 10°F; the maximum dew point on this date is 40°F in 1977; and the minimum dew point on this date is -22 degrees F in 1983.

All-time state records for December 17th:

The state record high temperature for this date is 63 degrees F at Farmington (Dakota County) in 1939. The state record low temperature for this date is -44 degrees F at Mora (Kanabec County) in 1983. The state record precipitation for this date is 1.80 inches at Hinckley (Pine County) in 1984. Record snowfall is 15.0 inches at Beaver Bay (Lake County) in 1863.

Past Weather Features:

The warmest December 17th in state history was in 1939 when many communities in Minnesota saw afternoon high temperatures climb into the 50s and 60s F. With little or no snow on the ground, even the overnight low at Winona was a mild 43°F.

An Arctic air mass occupied the state on December 17, 1983 sending overnight low temperatures into the minus twenties and minus thirties. Warmest spot in the wee hours of the morning was Grand Marais with a reading of -10°F. The high temperature at Wannaska (Roseau County) was -21°F. It was the start of a week-long episode of record-setting cold temperatures leading up to Christmas.

A major winter storm brought 1 to 2 inches of precipitation (and 4-6 inches of snow) to portions of central and northeastern Minnesota over December 16-17, 1984. Gunflint Lake reported a record 2.57 inches of precipitation, while Grand Marais had 1.80 inches.


Partly cloudy with slightly cooler than normal temperatures over the weekend. It will be mostly a dry period next week with temperatures hanging around normal in most places and perhaps creeping to above normal values by Christmas Eve.

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