Summer like heat arrived early in the spring of 1934. The mercury was already beginning to rise well into the 80s the last few days of April with Huron South Dakota hitting 91 degrees on the 29th. Precious little in the way of precipitation fell during April 1934 with much of South Dakota receiving less than a third of an inch. Only 0.05 inches precipitation fell in Mitchell and 0.03 inches at Huron for the month. The dry ground and lack of vegetation set the stage for an unprecedented event that followed in the month of May.
Of all the weather records kept, one of the least likely to be broken would be for the hottest May on record. In Sioux City Iowa, the average temperature for May 1934 was 72.6 degrees, the hottest on record. The second warmest May on record is 69.0 degrees in 1939, a full 3.6 degrees cooler. In Sioux Falls South Dakota, May 1934 saw an average temperature of 70.4 degrees, also the hottest on record. The next warmest May on record is 67.4 degrees in 1939. Precipitation at both of these cities for the month of May was also the driest on record with 0.60 inches at Sioux City and 0.10 inches at Sioux Falls.
Many towns and cities across South Dakota and surrounding states saw their earliest occurrence of 100 degrees during May 1934. These locations and dates of occurrence include...
Sioux City IA 100 degrees May 6
Pierre SD 103 degrees May 8
Sisseton SD 109 degrees May 8
Huron SD 101 degrees May 8
Mitchell SD 102 degrees May 8
Mobridge SD 103 degrees May 8
Wood SD 103 degrees May 8
Brookings SD 100 degrees May 17
Dupree SD 100 degrees May 17
Vermillion SD 100 degrees May 18
Hot Springs SD 100 degrees May 18
Spencer IA 102 degrees May 18
Lemmon SD 102 degrees May 27
Watertown SD 102 degrees May 28
On May 30 1934 temperatures climbed to unprecedented heights across central and eastern South Dakota, southwest Minnesota and northwest Iowa. The hottest temperatures occurred across northeast South Dakota where the mercury exceeded 110 degrees. In fact the 113 degree reading at Sisseton is the hottest temperature ever recorded in that town. A breakdown of high temperatures that day include...
Pierre 103 degrees Sioux Falls 104 degrees
Brookings 106 degrees Huron 106 degrees
Watertown 106 degrees Yankton 107 degrees
Academy 108 degrees Highmore 108 degrees
Mitchell 108 degrees Aberdeen 110 degrees
Redfield 113 degrees Sisseton 113 degrees
Sioux City 105 degrees Storm Lake 107 degrees
Le Mars 108 degrees Spencer 109 degrees
Tracy 107 degrees Pipestone 108 degrees
Academy recorded ten days of 100 degrees or more for the month including five in a row, May 16 through the 20th and four in a row, May 28 through 31st.
Mitchell recorded nine days of 100 degrees or more including four in a row twice, May 17 through the 20th and May 28 through the 31st.
Redfield also record nine days of 100 degrees or more for the month including four in a row, May 28 through the 31st and three in a row, May 16 through the 18th.
Yankton recorded eight days of 100 degrees or more including four in a row twice, May 17 through the 20th and May 28 through the 31st.
Wood also recorded eight days of 100 degree or more heat for the month including four in a row, May 28 through the 31st.
Sisseton recorded seven days of 100 degrees or more including four in a row, May 28 through the 31st with temperatures of 110 degrees on the 28th, 100 degrees on the 29th, 113 degrees on the 30th and 110 degrees on the 31st.
Highmore recorded seven days of 100 degree heat including four in a row, May 28 through the 31st.
Mobridge, Huron and Pierre recorded six days of 100 degrees or more for the month.
Brookings, Dupree, Vermillion and Spencer all recorded five days of 100 degrees or more for the month.
Precipitation for the month of May was well below normal with many areas reporting less than one half inch for the month. Sioux Falls only had 0.10 inches, Lemmon 0.08 inches, Dupree 0.07 inches and Camp Crook only 0.04 inches. At 1.49 inches, Brookings reported the most precipitation for the month. Mitchell received 1.15 inches rainfall and Vermillion 1.10 inches.
The magnitude and duration of the heat during May 1934 would have been an impressive event for the month of July, normally the hottest month of the year. It should be noted that several other days during the month saw temperatures climb into the 90s. The fact that it occurred during the month of May makes this a truly unusual event. Evidently a weather pattern more typical of mid summer developed over the middle United States in May. A strong and permanent ridge aloft would have allowed for ample subsidence or a downward motion of air from aloft. This sinking air would inhibit convection and produce warmer temperatures due to compression and adiabatic heating. Storm systems approaching from the Pacific Ocean would have been deflected north into Canada due to the proximity of the upper level ridge.
Above normal rains and cooler temperatures during June 1934 brought some relief to heat weary residents of South Dakota and its surrounding states. Hot and drier conditions returned in July and August although not to the extent that occurred in May.