The Milding of February: All-Time Winter Warmth in Midwest

Residents of Wisconsin have never experienced a winter day like the one that enveloped the state in a springlike balm on Wednesday. An uncommon lack of late-February snow cover across Illinois and southern Wisconsin allowed very mild air streaming northward to sweep across the state with very little surface cooling. All three of Wisconsin’s largest cities saw the highest temperatures observed on any December, January, or February day in more than a century of recordkeeping. Milwaukee’s 71°F smashed its winter record of 68°F (Dec. 5, 2001 and Feb. 11, 1999). Madison’s 68°F beat out 65°F from Dec. 3, 2012, as well as the monthly record of 64°F from Feb. 25, 2000. Meanwhile, Green Bay’s 65°F eclipsed the previous winter record of 64°F (Dec. 5, 2001) and the monthly record of 61°F (Feb. 26, 2000).

Wednesday’s warmth was a fitting coda to a remarkably warm stretch across most of the Midwest. In some ways, the ultra-mild period is reminiscent of the Great Warm Wave of March 2012, if not quite as spectacular as that summerlike spell was. Duration is one of the most impressive aspects of the past week’s Midwestern mildness. St. Cloud, Minnesota, saw its sixth consecutive day above 50°F on Wednesday, the longest such streak on record for any February, while Chicago, Illinois, set a similar record for its first six-day streak of 60°F readings in any February (or in any winter month, for that matter). Rockford, Illinois, set six daily record highs in a row on February 17-22. Each of these new records was between 66°F and 70°F, beating out previous records that ranged from 58°F to 64°F.

In Detroit, Michigan, the high on Wednesday hit 65°F, and was already at 66°F at 1 pm Thursday, marking the third and fourth time in the past week the Motor City has reached or exceeded 65°F. The forecast for Friday calls for a fifth February 2017 day of 65°F or greater, with a high of 67°F—a full thirty degrees above average.  Between 1874 and 2016, Detroit reached or exceeded 65°F only six times in February. Jeff Masters reports from southeast Michigan: “My lawn is starting to green up--an extraordinary occurrence for a time of year when the ground is usually frozen and covered with a hefty layer of snow!”


Figure 1. Spring in February? A crocus blooms in Dravosburg, Pennsylvania on February 20, 2017. Image credit: Wunderphotographer gingyb


Figure 2. Snow cover was lacking across the Northern Great Lakes on Wednesday, February 22, 2017. Image credit: NOAA/NWS/National Operational Hydrologic Remote Sensing Center.

Snow is a rare commodity in the Upper Midwest right now
Only 26.5% of the Upper Midwest was covered by snow on Wednesday, with an average coating of just 1.7 inches. Even the Northern Great Lakes were just 27.2% snow-covered. These are striking numbers to witness a full month before the spring equinox. The only states in the contiguous U.S. east of the Rockies where snow cover truly predominated on Wednesday were North Dakota, New York (the eastern half), and the New England states, still buried after a sequence of storms earlier this month.

Lake ice is also in relatively short supply across the Midwest. Only 8.7% of the Great Lakes were ice-covered as of Tuesday, compared to 12.7% on that date in 2016 and a far more impressive 82.8% in 2015. It appears that the maximum coverage this year will be the already-observed 15%. That would place 2015-16 in fourth place for lowest maximum ice extent among all winters tracked since 1973 by NOAA, as related by George Leshkevich (NOAA Great Lakes Environmental Research Laboratory) to the Detroit Free Press.

Back to a more late-winter-like pattern
A strong, blustery winter storm pushing across the Midwest late Wednesday into Thursday will send the region back into a more seasonable pattern for at least a few days, starting off with a swath of snow extending from Colorado and Wyoming across the central and northern Great Plains into the Midwest. After reaching the mid-60s on Wednesday (35°F above average), Green Bay was expecting 1” - 3” of snow late Thursday into Friday. A blizzard warning was in effect for Thursday night into Friday across northwest Iowa and neighboring areas. It looks like Chicago will get mostly rain until at least Friday, thus prolonging its record-long “snow drought.” As of Wednesday, it had been 67 days since Chicago got its last inch of snow, surpassing the record of 66 days (Dec. 25, 1921, to Feb. 28, 1922).

We’ll be back with a new post by Friday afternoon. Stay tuned for more in coming days on how this strikingly mild late winter is affecting other parts of the U.S.

Bob Henson