Since the new millennium started in the year 2000, Minnesota has only recorded four drier-than-normal months of October on a statewide basis. These four years were 2003, 2006, 2011 and 2014.

In all four of those years, the statewide average rainfall was about 1 inch, plus or minus a tenth of an inch. But for some of Minnesota’s prime agricultural counties, where the majority of the land is devoted to crop production, these Octobers were near record-setting in terms of rainfall:

In all of these cases, the very dry month of October was a detriment to the next cropping season, as October rainfall is one of the critical weather features to recharging that season’s soil moisture. Studies have shown that up to 80% to 90% of the precipitation in October goes into soil moisture storage, one of the highest moisture-storage efficiencies of any month of the year.

Low humidity, fire danger

A second feature of these exceptionally dry Octobers is the extremely low relative humidity that accompanies them and aggravates a higher fire danger. These dry Octobers brought very few days with rain — only two to five days in many cases. The vast majority of days were sunny and dry, with very low relative humidity.

For example, during 2003 a string of very dry days in mid-October brought relative humidity as low as 17% in Martin County along the Iowa border. In October 2006, Montevideo in Chippewa County reported several days with afternoon relative humidity from 14% to 16%.

In October 2011, when some of the driest air was located over the Red River Valley in northwestern Minnesota, some afternoon relative humidity readings were only 16% to 17%. October 2014 brought very low relative humidity to west-central counties, with afternoon readings that ranged from 14% to 16%.

Also on some days during these October months, the very low relative humidity readings — when combined with wind gusts of 25 mph or greater — caused the National Weather Service to issue red flag warnings associated with the risk of wildfires.

October is often feast or famine when it comes to rainfall in Minnesota. When it is dry it is very dry, but when it is wet it can be extremely wet. For example, in 2009, the statewide average rainfall in Minnesota was over 5 inches, with some locations reporting 7 to 9 inches of total rainfall. And as recently as 2019, the statewide average October rainfall was over 4 inches, with some areas reporting 6 to 7 inches.

What will October 2022 bring? Based on the yearly weather pattern so far, models are leaning towards a drier-than-normal month.

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