The 2023 Mid-April Heat Wave

An extremely warm air mass for so early in the year surged across Minnesota April 11-14, eating through the large lingering snowpack and setting daily temperature records.

A broad area of southwesterly flow, stuck between high pressure to the east and low pressure to the west, began pulling dry and warm air into Minnesota on on Monday April 10, 2023. That first day was a "primer" day, with the warm air establishing itself, melting some snow, and preparing Minnesota for the next 3-4 days of much stronger heating.

By Tuesday, temperatures in the 70s surged up to the Canadian border, and with 80s covering the southern third of the state. Despite having a foot of snow on the ground as the day began, International Falls reached 71 degrees F. Deep snow generally resists strong heating because the snow reflects the sunlight, preventing it from warming the ground and the air. This, however, was an extremely warm air mass.

The heat intensified and expanded on Wednesday, with 80s and some low-90s covering all of the the south, and 70s again widespread across the north. The heat broke over parts of the north and west Wednesday evening, but continued in much of the south and east not only on Thursday, but also on Friday. The Twin Cities recorded four straight days with high temperatures in the 80s F, which had never been recorded previously during the first half of April.

The highest temperature recorded in the state during this  period was 95 F at Theilman in southeastern Minnesota. This sensor may have been reading erroneously high, but several  temperature stations and airports did record high temperatures of 90 F in the southern third of the state. The highest temperature recorded in the Twin Cities was a daily high temperature record 88 F on Wednesday April 12th; on April 13th, the Twin Cities reached 87 degrees F, setting another record.

Other high temperature records were set in Rochester on the 12th and 13th, with 87 F and 83 F, respectively, and at St. Cloud, which recorded 86 F on the 13th.

The warmth made a huge dent in the area snow cover. On April 6th, about 50 percent of Minnesota had 18 inches of snow on the ground or more, with many areas over two feet, and all but the southeastern third of the state at the 99th percentile for early-April snow depth. By Thursday April 13, the snow had melted entirely over the rest of southern and much of central Minnesota, and 1-2 feet had melted from northern Minnesota, with most of the state now in the middle percentiles (meaning slightly below or above historical averages) for mid-April snow depth.

The heat also supercharged the lake ice-outs, with dozens of lakes opening up in southern Minnesota. Other types of phenology caught up quickly as well. Siberian squill carpeted the wooded hills near the St. Paul campus of the University of Minnesota by Tuesday April 11, which is within one day of average emergence. Many trees across southern Minnesota began popping out leaf buds as well.


Updated Friday April 14, 2023.



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