Above-Normal Temperatures Dominate the Midwest

The entire Midwest experienced above normal temperatures this week (Figure 1). The largest temperature departures extended from Missouri, Iowa and into northern Michigan. Many of these locations were between 11-13°F above normal with isolated locations ranging from 13-19°F above normal. Rock Island County, Illinois, recorded an average temperature of 78.6°F, which was 18.9°F above normal for the week. The highest maximum temperature of 96°F occurred on May 11. Maximum temperatures followed suit, with the largest departures occurring in northern Michigan (Figure 2). Minimum temperatures also followed similar patterns, but with less extreme departures (Figure 3). Across the entire Midwest, there were 849 high maximum and 652 high minimum temperature records broken or tied this week (Figure 4). Modified Growing Degree Days (MGDDs) rebounded this week with many locations across the Midwest slashing deficits that had accumulated since April 1 (Figure 5). Trent Ford, Illinois State Climatologist, tweeted about the significance of this week’s heat wave calling it an unusual event given the cold weather leading up to the event. Unfortunately, there were three heat related deaths in Chicago.

Minnesota Receives Heavy Precipitation, Everyone Else – Not so Much

South-central Minnesota had a bullseye for heavy precipitation ranging from 2.5 to 4 inches and isolated locations receiving up to 5 inches (Figure 6). Many stations in Minnesota received over 300 percent of mean precipitation with some reaching up to 750 percent of mean precipitation (Figure 7). Many rounds of thunderstorms contributed to these heavy precipitation totals. Stearn County, Minnesota received 5.8 inches of precipitation, which was 4.84 inches above normal. The heaviest 1-day maximum total of 2.72 inches occurred on May 12. Many river and stream gauges in western and central Minnesota remained at or above flood stage with the addition of heavy precipitation (Figure 8). To the east, northern Wisconsin received 1.5 to 2 inches of precipitation, which was 150 to 300 percent of normal. Most of the Midwest, however, received less than 50 percent of normal precipitation. There were 84 stations across the Midwest, most concentrated in Minnesota and Wisconsin, where daily precipitation records were broken or tied this week (Figure 9). Drought improvement was seen in northern Iowa (Figure 10).

Heat Brings Severe Storms in Upper Midwest, Isolated Events in Lower Midwest

There were 17 tornado, 292 hail, and 204 wind reports this week (Figure 11). Additionally, there were 31 occurrences where hail was in excess of 2 inches and 42 reports of winds in excess of 65 knots. Every day this week had storm reports as it was one of the most active weeks in a while. On May 9, three locations in Minnesota reported hail that was 3 inches in diameter. Hail in Washburn County, Wisconsin was large enough to bust windows out of buildings. Minnesota had 6 preliminary reports of tornadoes on May 11, and a confirmed EF-0 in Coon Rapids. The excessive wind event on May 12 that ended in Minnesota even was coined the “D” word... Derecho. The Storm Prediction Center tweeted that there were 55 preliminary reports where wind speeds were in excess of 75 mph, making it the second most since 2004. Osceola County, Iowa recorded an 82-mph wind gust and also created a dust storm. There were two fatalities associated with the May 12 storms in Minnesota. There were many trees uprooted, powerlines downed, and damage to buildings across Iowa and Minnesota. On May 13-14, the storm system migrated and delivered tornado, hail, and wind storm reports across Wisconsin, Missouri Illinois, Indiana, Kentucky and Ohio.