May 2017
Monthly Overview - May 2017
Seasonal Temperatures
Temperatures in May averaged to within a couple degrees of normal across nearly all of the Midwest, with areas bordering Lake Superior 2-4°F below normal
(Figure 1). Daily temperature records during the month were mostly record low maximum temperatures in the first few days of May, followed by some record high temperatures on the 16th through the 18th, then more record low maximum temperatures from the 20th to the 23rd. The number of record highs (over 300) and record lows (nearly 500) were fairly even and not particularly numerous, as expected with average temperatures near normal. Spring temperatures (March-May) were near normal in the northern half of the region and slightly above normal in the southern half of the region (Figure 2).
Soaking Rains for Some
Rainfall totals for the Midwest in May ranged from just over an inch in northwestern Minnesota to more than six inches across large swaths of the region (Figure 3), including parts of all nine Midwest states. A handful of stations in each of Illinois, Indiana, Kentucky, Minnesota, and Missouri topped 10 inches for the month. Totals were below normal in northwestern Minnesota, northern Missouri to southeastern Iowa and parts of western Illinois, much of Lower Michigan, and scattered pockets in the Ohio River Basin (Figure 4). The rest of the region, more than half by area, was above normal and in many locations well above normal. Only northwestern Minnesota had locations with less than 50% of normal while all nine states had locations with 150% of normal for the month (Figure 5).
Flooding that began in late April in Missouri, Illinois, and Indiana continued with heavy rains in early May. Rivers in these areas rose again with more rain around the 20th and 21st. Flooding also occurred in southern Minnesota and western Wisconsin during the middle of May with heavy rains in those areas. The high rainfall totals and associated flooding meant that many fields would need to be replanted.
Spring rainfall totals were above normal for nearly all of the Midwest (Figure 6). Only northwestern Minnesota and some smaller areas in Kentucky had less than normal for the 3-month period. Totals for the spring topped 150% of normal in many locations with much of southern Missouri topping 200% of normal for the season. The spring ranked as the 6th wettest on record (1895-2017) for the region as a whole with 127% of normal. Statewide ranking for six states (MO 4th, WI 5th, MI 9th, IN 10th, OH 11th, and IL 12th) were among the wettest 10% of springs in their history.
Lack of Midwest Drought
Rains in late April and early May contributed to the removal of all drought and abnormally dry designations from the Midwest. The complete lack of both drought and abnormally dry conditions in the May 2nd US Drought Monitor
(Figure 7) last occurred in May 2002. Abnormally dry conditions in northwestern Minnesota then expanded during May to cover just under 5% of the Midwest by the May 30th US Drought Monitor (Figure 8).
Severe Weather
May saw numerous reports of severe thunderstorms with tornado reports on 11 different days and in seven states. Large hail was reported on 18 days and severe winds on 19 days. There were seven days with no severe weather reported and another 11 days with fewer than 10 reports in the region. During the month there were nearly 1500 reports of severe weather with five days (15th-18th and 27th) each with over 100 reports. Michigan was largely spared with just three reports of severe weather for the entire month.
An EF-2 tornado on the 16th near Barron, WI
(Barron County) was responsible for one death and at least 20 injuries. Strong non-thunderstorm winds on the 17th across Missouri and Illinois also caused fatalities. In Sikeston, MO
(New Madrid County) a rotten tree was blown down killing one person. In central Illinois, dust storms whipped up by 40-50 mph winds from Springfield to just south of Champaign closed I-72 for stretches and led to a multi-vehicle accident on US-36 near Tuscola, IL
(Douglas County) with one death.
Last Gasps of Winter in the North
Snowfall totals in May were limited to a couple inches at some Wisconsin
(Figure 9), Michigan (Figure 10), and Iowa
(Figure 11) stations while totals in Minnesota (Figure 12) ranged up to seven inches. The last freeze of the season occurred during May for many of the northern communities in the region, with freezing temperatures also reaching as far south as southern Indiana and Ohio along with a few Kentucky stations
(Figure 13). Temperatures in May dropped below freezing at stations in every state except Missouri with temperatures dropping into the lower 20s at locations in Minnesota, Wisconsin, and Michigan. In Michigan, fruit trees suffered some damage from freezing temperatures on the 8th and 9th.
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The Iowa Climatology Bureau also contributed to this report.
The Minnesota State Climatology Office also contributed to this report.