A look at weather extremes and the big-picture climate connections.

Rare May Snowstorm Annihilates Records in Midwest

A late spring snowstorm in the Midwest has shattered longstanding state snowfall records, with all-time state records for the month of May falling in Iowa, Minnesota, and Wisconsin. The snowstorm, which walloped the region with snowfall rates of more than an inch per hour at times on May 1-2, delivered 18 inches of snow in Blooming Prairie, Minn., 17.5 inches in Goodhue, and 15.5 inches in Owatonna.

Snowfall measurement in Eau Claire, Wis. 
Credit: NWS.

According to the Minnesota Climate Working Group, the state daily May snowfall record had stood at 12 inches, which was most recently set on May 3, 1954. The Working Group said that the snowstorm was extremely rare for southern parts of the state. 

“While May snowfalls are not uncommon in northern Minnesota, heavy May snowfall in southern Minnesota is rare. A quick scan of all historical Minnesota May daily snowfall totals greater than or equal to 3 inches indicates that May 1938 may have been the last time any southern Minnesota observer reported snowfall totals of similar magnitude,” the Working Group said on its website.

In Iowa, the 11 inches recorded at the town of Britt, which is in the north central part of the state, is also likely a state record. The 6.7 inches that fell in Des Moines was the city's biggest May snowstorm on record. In Wisconsin, 16.2 inches fell at Ashland, which also set a state record for the heaviest May snowstorm on record.

Also, up to 3 inches of snow fell in Arkansas, where measurable snow had never before been recorded in May.

One of the major impacts of climate change on the U.S. has been an increase in extreme precipitation events, such as record daily rain and snowstorms, according to a forthcoming federal climate assessment. As air and water temperatures warm, the more moisture is added to the atmosphere, where it can be tapped by storms to produce heavier amounts of rain or snow.

The storm resulted from a sharp dip in the jet stream across the West and Midwest, which drove cold air southward from Canada, causing record-cold temperatures as far south as Texas. Meanwhile, to the east, an area of high pressure over the eastern seaboard, and an area of low pressure in the upper layers of the atmosphere over the Western Atlantic, effectively blocked the eastward progress of the storm, keeping it in place for more than 24 hours and allowing it to dump heavy amounts of precipitation.

Map of upper-level winds, with annotations to show upper level Lows (L) and Highs (L) along with the general direction of upper level winds.
Click image to enlarge. Credit: Weatherbell.com/Climate Central.

Meteorologists refer to this type of weather pattern as an Omega Block, since the upper air flow’s twists and turns resemble the Greek letter omega.

The frontal boundary that dumped the snowfall is moving eastward, and it is expected to bring potentially flooding rains to the Lower to Middle Mississippi and Tennessee River Valleys

As the National Weather Service reported in an online forecast discussion, “The sluggish progression of the front . . . combined with plenty of moisture streaming out of the Gulf and Atlantic . . . should fuel an organized band of moderate to heavy rains along the front. Flooding and flash flooding will be a concern with this system . . . especially as it dumps rain on the already swollen rivers of the Mississippi."

The weather pattern has contributed to overall colder-than-average and wetter-than-average conditions during the past month across the West, parts of the Plains, and Midwest. Between April 3 and May 2, for example, 4,133 daily record-low temperatures were set across the lower 48 states, compared to just 656 daily record highs. In addition, 1,166 daily snowfall records were set during this period, according to the National Climatic Data Center in Asheville, N.C.

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