Soaking-Wet Holiday Heat Wave!

city intersection at night with streetlights

A bank marquee tells the story of a warm winter evening in Rochester on December 23, 2023.

Courtesy: Minnesota State Climatology Office

An extremely warm and humid winter air mass obliterated temperature, dew point, and even some precipitation records on Christmas Eve and Christmas Day, 2023, across Minnesota.

The stage was set for unusually warm conditions across the state because the flow pattern for most of the already-warm December had kept cold, winter-like air masses bottled up in northern Canada, leaving mild air over Minnesota. As a series of low-pressure systems moved out of the southwestern US from Saturday the 23rd through Monday the 25th, they brought surges of very warm and humid air into the region, accompanied by waves of rain, and just the faintest accumulations of wet snow late in northwestern and northern Minnesota.

The warm, humid, and wet conditions set a surreal holiday scene, with grasses brightening up, Minnesotans walking outside in light clothing, holiday lights reflecting off of street puddles, and scarcely any snow to be found.

Record Warmth

The temperatures had already been elevated for most if not all of the month, but the first hints of a new surge of warmth could be detected on Friday December 22, as temperatures remained above freezing for the entire day across virtually all of the state. Temperatures increased by 5-10 degrees F on Saturday the 23rd, and then jumped another 5-10 degrees F in most places as they peaked Christmas Eve and Christmas Day - December 24 and 25th. During this time, high temperatures were in the 50s F and low temperatures in the 40s F across southern and eastern Minnesota, with highs generally in the 40s F and lows in the 30s F elsewhere.

It was the warmest December 24th on record at each of Minnesota's five "first-order" climate stations, with Duluth, International Falls, Rochester, St. Cloud, and the Twin Cities all observing both the highest high temperature, and the highest low temperature on record for the date. December 25th nearly repeated the feat, except the high temperature of 33 F at International Falls missed the daily record; the other stations all broke daily high temperature records, and all of them, including International Falls, broke the record again for the highest low temperature for the date.

The daily high temperatures were quite unusual, but it was the daily minimum temperatures (the lows) that stood out most. Some of the daily low temperature were 6-10 degrees higher than any other low temperature on record for the date -- a huge margin given the long records of these stations. Many of the low temperature values are now the highest for any date between early or mid-December, and late February or early March.

Below is a table of daily highs and lows at Minnesota's five major climate stations, from December 22 through December 26, 2023. Bold numerals indicate a record for that date.

Daily maximum and minimum temperatures in deg. F

Date	Duluth	International Falls	Rochester	St. Cloud	Twin Cities
Fri 12/22	35/33	36/34	43/34	39/35	43/36
Sat 12/23	41/35	41/35	46/39	45/38	48/40
Sun 12/24	48/41	47/33	52/44	52/38	55/45
Mon 12/25	46/36	33/30	53/44	48/36	54/42

Record Humidity

With the warm air came a record-shattering surge of moisture, easily the strongest to occur so late in the season. Dew point temperatures surged into the 40s F through the Boundary Waters and as far northwest as Crookston, with values reaching or exceeding 50 F throughout the eastern and southern Minnesota. These, too, are extraordinarily high values for so late into winter, and in many cases represent the highest recorded values for any date during an 8 to 12-week block extending deep into or through February.

For instance, the dew point of 45 F recorded at International Falls at 2 PM on December 24th is not only the highest on record for any date from early December into late February at that location, but also would have set a daily record at any of the much more humid southern Minnesota stations, including the Twin Cities and Rochester.

The Twin Cities broke three consecutive daily dew point records, with the 50 and 51 F values on the 24th and 25th, respectively, breaking previous records by over 10 F. This event expanded the range of dates with 50-degree (or higher) dew points in the Twin Cities by 10 days. The range of dates had just by expanded 10 days In 2021, because of rare warmth and moisture associated with a destructive severe weather outbreak. Thus, in just over two years' time, the latest date with a 50-degree F dew point in the Twin Cities has advanced 20 days, from December 5th to December 25th.

Record Precipitation Too!

Map of total precipitation for the 72-hour period ending 7 AM on December 26, 2023. Based on combined data sources. Labeled values may not match exact observations at those locations.

Courtesy: National Weather Service Forecast Office, Chanhassen

Not to be outdone by chart-topping temperature and dew point performances, this system also produced widespread precipitation, almost entirely in the form of rain. The precipitation stretched from late on the 23rd in western Minnesota, to the morning of Tuesday December 26th. Duluth, International Falls, and St. Cloud each set daily precipitation precipitation records for December 24th, including 1.47 inches at St. Cloud. The highest daily or 24-hour precipitation total was 2.63 inches, recorded on the morning of the 26th at Watson, which is in western Minnesota between the Chippewa and Minnesota rivers. Glenwood had a daily total of 2.27 inches, also on the 26th. At both stations, this represents the largest daily precipitation total of the year, a distinction almost always reserved for the warm months.

Most of Minnesota, minus the northwest, northeast, and far southeast corners, received at least an inch of precipitation, and nearly 60% of the state received 1.5 inches or more. The highest totals recorded by National Weather Service cooperative observers through the morning of December 26 included 3.32 inches at Litchfield and 3.07 inches at Bird Island. Some CoCoRaHS observers in central and western Minnesota also recorded over three inches for the event, including a high of 3.52 inches reported near Big Lake. In these areas, 3-day precipitation totals exceeded the normal precipitation for the entire December-through-February winter.

Effectively No Snow

Minnesotans, and those familiar with our wintry state, could not be blamed for assuming that a storm system producing 1-3 inches of precipitation in late-December also would have been a whopper of a snow storm. Given the major holiday, it would have seemed fitting to have roads shut down and travelers stranded from all directions. Yet this storm produced almost no snow snow in Minnesota, and perhaps its oddest feature was the utter lack of cold air anywhere in the state, even on the northwest side of the circulation. As a result, precipitation was almost entirely rain, with mixed precipitation at times on the state's far northern and western borders, and snow accumulations uniformly under an inch, if and where any snow fell at all, generally in northwestern and northern parts of Minnesota.

As the 26th wore on, accumulating snows were falling in parts of northwestern and far northern Minnesota, but only after 90-95% of the precipitation had already fallen.

Turning Up the Heat on a Champion

Prior to this event, December 2023 was already running in the top-10 for warmth across Minnesota, but after it, most stations were ranked at or near the top spot. For Duluth and the Twin Cities, the year to beat is 1877, which has been unchallenged by other Decembers for over 145 years. As of the 26th, however, December of 2023 is a definite contender, with the Twin Cities running slightly ahead. Breaking monthly temperature records from December 1877 would be a historic event indeed.

Updated December 26, 2023