A look at weather extremes and the big-picture climate connections.

Heat Wave Sends Temps Soaring into Uncharted Territory

The March heat wave went from extreme to downright unprecedented in parts of the Midwest on Tuesday, as Chicago, Detroit and areas all the way north into Canada shattered longstanding records. So many records have been broken — 3,550 record daily highs and 3,109 daily warm low temperature records during the March 12-18 period — that it’s difficult to sort through them all. In Chicago, where the temperature rose to 85°F, an all-time record high for the month and the record sixth March 80-degree day, a National Weather Service (NWS) forecaster described the situation as “unreal.” Through Tuesday, the city had set warm temperature records seven days in a row — with more records likely to fall Wednesday and possibly Thursday.

"It is remarkable enough to watch longstanding all-time record temps be threatened . . . but the total scope (duration and intensity) of this warm spell is something that has [been] historic and [is] unlikely to be matched in our liftetime,” read an NWS forecast discussion on Tuesday.

Locations that set daily high temperature records on March 19. Credit: NOAA/NCDC.

With temperatures forecast to once again soar into the 80s today in the Windy City, think about the warmth this way — as an NWS meteorologist noted, only once in the 140 recorded years of weather observations has April produced as many 80°F days as have been observed so far this March in Chicago.

The volume of records being set during this long-duration heat wave is staggering. On March 18 alone there were 1,597 warm temperature records set or tied in the U.S., compared to just 58 cold temperature records. For the year-to-date, there have been 14,737 warm temperature records set or tied, compared to 1,296 cold records — a ratio of about 11-to-1.

Among these figures are many record warm overnight low temperature readings. On March 19, 555 daily highest-minimum temperature records were set or tied, compared to 435 daily record highs. In some cases, the overnight low temperature was warm enough to break a daily high temperature record, which is no easy feat in any month, let alone March.

In a long-term trend that has been found to be inconsistent with natural variability alone, daily record-high temperatures have recently been outpacing daily record-lows by an average of 2-to-1, and this imbalance is expected to grow as the climate continues to warm. According to a 2009 study, if the climate were not warming, this ratio would be expected to be even. Other studies have shown that climate change increases the odds of extreme heat events and may make them warmer and longer lasting.

Land surface temperature anomalies during the period March 8-15. Click on image for a larger version. Credit: NASA.

Record warmth also spread across the state of Michigan yesterday. Traverse City set an all-time March high temperature record with 86°F on Tuesday, its fourth 80-degree reading since March 17. Detroit, Flint, and Saginaw all broke daily records on Tuesday as well. Grand Rapids, Lansing and Muskegon broke all-time monthly records, with high temperatures in the lower 80s. According to the NWS, the only early-season warm spell that compares to this one in Detroit occurred in April 1886.

In Marquette, Mich., located along the shores of Lake Superior, the temperature of 78°F tied an all-time monthly record. Marquette also tied its daily low temperature record, as temperatures only dropped to 54 degrees. The average high temperature at Marquette this time of year is 36 degrees, with a typical low of 15. The observed high and low, were closer to typical mid-July values.

The NWS office in Detroit released a statement on the warm weather, noting that it follows on the heels of Detroit’s fifth-warmest winter on record, an unusually warm fall, and a summer that included the city’s warmest July on record. “In fact, the jet stream has been displaced well north of its typical position since the middle of last year,” the NWS stated. “Now, with none of the typical ice on the Great Lakes to insulate Michigan from the effects of this unusually warm spring, record warmth has been allowed to surge into the state like never before.”

Jet stream winds on Tuesday, March 20, showing the strongest winds blowing (reds and orange colors) from south to north into Canada, drawing warm air in that direction. Credit: NCAR.

Water temperatures in the Great Lakes are indeed climbing sharply in response to the heat wave, and the NWS said that the water temperature in Lake Michigan might have set a record for the warmest reading so early in the year.

Record warmth also spread into Wisconsin again Tuesday. In Green Bay, the temperature reached 80°F, the earliest such reading on record. Prior to Tuesday, there had only been one 80-degree day in March in 120 years of recordkeeping.

The warm weather also extended farther east Tuesday, with Caribou, Maine setting a record for the earliest 70-degree reading, as the temperature made it to 73°F, tying the all-time March high for that location. What’s especially remarkable about that record is that there was still nine inches of snow on the ground as of yesterday.

Canada, too, basked in the warm weather for another day. Moosonee, Ontario, for example, reached 70°F, a downright tropical reading compared to its normal high for the date of 25°F. Winnipeg, Manitoba set a record high for the month of March, with 74.7°F, beating the previous record of 73.9°F, set in 1946.

The heat dome is expected to contract and slide eastward during the next few days, with forecast highs in New England on Thursday reaching the 70s to 80s. Slow-moving heavy rains and severe weather have been plaguing the central and southern U.S. at the boundary between a cooler air mass and the very warm air. 

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