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April 1980: Unprecedented Heat in the Northern Plains

by Joe Sheehan
National Weather Service
Sioux Falls, SD

During April 1980 unprecedented heat occurred across the Northern Plains. Thermometers across this region rose into the 90s on April 20-21 and across Iowa on the 22^nd. These temperatures were 40 to 45 degrees above normal for the date. On the 21^st, 100 degree temperatures were concentrated along the North Dakota-Minnesota border almost as far north as the Canadian border! On the 22^nd the hottest temperatures of  95 to 100 degrees were located along highway 20 in Iowa between Sioux City and Dubuque. These excessive temperatures not only broke daily record highs, but were the warmest readings recorded for so early in the season. Normal high temperatures for April 21^st  are 55 degrees at Grand Forks N.D., 57 degrees at Fargo N.D., 60 degrees in Aberdeen S.D., and 62 degrees at Waterloo IA.

The 100 degree readings at Waterloo, Iowa and Grand Forks, North Dakota tied the hottest temperature recorded that year, as Waterloo hit 100 degrees on July 17^th and Grand Forks reached 100 degrees on July 10^th. Other locations saw only  one other day during July with a hotter temperature reading. Also, at many of these locations the April 21 temperatures were hotter than any temperature the pervious summer. 

The 101 degrees recorded on April 21^st at Oakes, North Dakota and Hawley, Minnesota represents their  states’ hottest April temperature. The 100 degree  reading on April 22^nd at Fort Dodge and Waterloo are the hottest temperatures recorded for the month of April in Iowa. Finally the 100 degrees recorded at Britton on the 21^st  is the hottest temperature recorded during April in South Dakota.

100 degree temperatures for April 21, 1980
 and hottest summer temperature

100 degree temperatures for April 22, 1980
  and hottest summer temperature

A strong ridge in the upper atmosphere was located over the central U.S. during this period. This ridge  provided strong subsidence across the region. Compression and warming occurred as this air mass sunk earthward resulting in clear skies across the region. Surface dew point temperatures were low, in the 30s and 40s, so there was a larger diurnal range in temperature because dry air will warm or cool faster than moist air. Also, below normal precipitation during the months of March and April helped to set up a desert- like climate. Only a trace of precipitation was recorded during the month of April at Grand Forks, North Dakota and Ada, Minnesota. Other meager April rainfall amounts were recorded at Hawley, Minnesota, (0.01 in.) and at Fargo, North Dakota, (0.02 in.)

 At the surface, a warm front extended across southwest Manitoba, Canada into northeast North Dakota early Sunday morning on April 20^th. Later that afternoon temperatures rose into the upper 80s to the middle 90s across the Dakotas, Nebraska and the western portions of Minnesota and Iowa. By the next morning, the warm front extended from International Falls, Minnesota to Keokuk, Iowa. The leading edge of cooler air was just entering northwest North Dakota. This would be the day when afternoon temperatures would climb to 100 degrees across western Minnesota and eastern North Dakota. On the morning of the 22^nd, a cold front extended from near International Minnesota to Chadron Nebraska bringing with it an end to the extreme heat across the Dakotas and western Minnesota. The day’s hottest temperatures would be found across Iowa with Fort Dodge and Waterloo hitting 100 degrees.

The summer of 1980 across the Northern Plains would see temperatures one to three degrees above normal  during June and July. Temperatures were below normal in August except in Iowa where temperatures were two degrees above normal at Fort Dodge and Waterloo.

The summer of 1980 would be more significant for the southern U.S. as that part of the country had one of its hottest summers on record. Dallas, Texas was especially hard hit by the summer heat as that city experienced its hottest summer with an average temperature of 89.2 degrees during the three month period June through August. The average high temperature during the summer was 101.6 degrees. The hottest July occurred this summer with an average temperature of 92 degrees and an average maximum for the month of  105.3 degrees. The city’s hottest temperature of 113 degrees fell on two days, June 26 and 27 in 1980. Dallas would go on to record 69 days with temperatures of 100 degrees or more that year, including 42 days consecutive from June 23^rd to August 3^rd.