Severe to extreme drought has been very rare for Minnesota historically during the autumn season. Spring and summer droughts are more common.

However, 100 years ago in the early autumn of 1918, an expanding growing-season rainfall deficit peaked during September, producing extreme to severe drought across northern and central Minnesota. It hit both the livestock industry through feed shortages, and the crop producers of Minnesota through reduced yields.

Following a near-normal August in terms of temperatures and rainfall, September 1918 began mild, with below-normal temperatures and low humidity. A number of counties reported small amounts of rainfall on the second of the month and again on the eighth, but otherwise the first three weeks of September were bone-dry.

Temperatures increased to above-normal values at times during the second half of the month, but the absence of rain continued. For many counties only two more rains came, small amounts on both the 18th and the 29th. The dry air and clear skies brought multiple overnight frosts as well.

Historic dryness
By the time the month concluded, the University of Minnesota Agricultural Experiment Stations at Crookston, Morris and Grand Rapids all reported less than a half-inch of total monthly rainfall. For some climate stations, it was historically dry, as Minnesota stations at Fergus Falls, Canby, Wheaton, Beardsley and Campbell all reported less than 0.20 inches for the month.

Based on the historical Palmer Drought Severity Index at the end of September 1918, nearly half of the state, mostly central and northern counties, reported severe to extreme drought. Overall, September 1918 was the driest in state history at the time. There have since that time been four drier Septembers statewide, all of them also associated with some seasonal drought.

As the drought peaked near the end of September 1918, the risk of wildfires was extreme. And sure enough, on Oct. 12, 1918, sparks from a railroad train passing near Sturgeon Lake, Minn., set off some timber-harvesting debris that had been left near the rail line.

High winds caused the fire to spread rapidly, and it evolved into a massive killer blaze. It devastated more than 1,500 square miles in northeastern Minnesota, killed hundreds of people and left thousands of citizens homeless.

Now known as the famous Cloquet-Moose Lake Fire, this disaster was directly related to the amplified autumn drought of September 1918. Many Minnesota families still have personal stories about it.

Since that time, only 1952, 1974, 1976 and 2012 have brought drier Septembers to the state.

Seeley is professor emeritus of climatology at the University of Minnesota.