Farm Progress

Climate Observations: A record temperature swing of 67 degrees F in one day occurred in May 1934.

Mark Seeley

March 31, 2017

2 Min Read
WHERE’S THE FROST? With wide temperature swings in May, fewer Minnesotans report frost on the landscape.Dendron/iStock/Thinkstock

Though May brings the occasional snowstorm, as it did in record-setting fashion in 2013, its weather pattern usually teases us with glimpses of summer-like conditions.

Several days may bring daytime temperatures in the 80s — perhaps even one or two 90-degree days. More than half of the calendar dates show a statewide record high of 100 degrees F or greater, topped by 112 degrees F at Maple Plain in Hennepin County on May 31, 1934.

Daily variation
For many agricultural areas of the state, the daily temperature range increases as the energy from the sun is amplified by longer day length and higher elevation angle. Southerly winds can usher in very warm air from the Southern Plains states, while easterly winds off the cold waters of Lake Superior or northwesterly winds from the prairie landscapes of western Canada can greatly suppress temperatures across Minnesota.

In many cases, the daily temperature range can fluctuate by 30 to 40 degrees F. An extreme case occurred May 16, 1934, at Milan in Chippewa County in western Minnesota. The morning low was just 34 degrees F. However, a strong sun and dry landscape allowed for rapid warming during the day and by late afternoon, the high temperature reached 100 degrees F, a rise of 67 degrees F, and a record high for the date.

Geographic variation
Still another feature of the May temperature pattern in Minnesota is widespread geographic variability around the state, depending on cloud cover and the direction of the winds. One portion of the state may be visited by summer-like conditions, while another part of the state may see a simultaneous return to winter.

Such was the case on May 19, 2009, when at 4 p.m., bright sunshine and southerly winds brought the temperature to a record-setting 100 degrees F at Milan in Chippewa County and Madison in Lac Qui Parle County, while at the same moment in time easterly winds off Lake Superior held the temperature at Grand Marais Harbor to a high of 34 degrees F.

Fewer frosts
Still, despite the amplified temperature differences across time and geography, one changing feature of climate in the month of May is the decline in the number of frosts. Many areas of the state that were once subject to frequent frosts in May now go for many years without any frost at all. This has expanded the growing season for both crop producers and the home gardener. In fact, Minnesota has seen its growing season increase more in length than just about any other state.

With the outlook favoring a warm May in 2017, I would not be surprised to see that frosts will be scarce around the state this time around.

Seeley is an Extension climatologist with the University of Minnesota.

About the Author(s)

Mark Seeley

Mark Seeley is an Extension professor emeritus of meteorology and climatology at the University of Minnesota.

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