May 2015: A Melting Pot of Seasons

Posted: June 4, 2015, 11:43 am by jmartucci

May 2015 had every aspect of weather you can imagine, typical of spring. Heavy rain, severe weather and yes, winter weather all greeted the month of May. Also much like spring, wide temperature variations were seen in the month, with most cities setting both record high and record low temperatures.

Coming off a 1 - 3° warmer than average April, the first day of May brought back memories of early spring. Illinois and Indiana woke up to low temperatures in the 30s and low 40s as a strong high pressure system brought clear skies and calm winds, perfect for radiational cooling. Record low temperatures were broken in Rockford, IL (34°F), Chicago (38°F) and Indianapolis (39°F). Temperatures moderated for the next several days, before a warm front lifted into Illinois on the 4th. This warm front became stationary across the Mid-West, bringing several days of unsettled weather. Chicago and Dayton, OH both set daily rainfall records on the 5th, at 0.95” and 0.57”, respectively. Columbus saw near 0.75” of rain, too, but Cincinnati and Indy only saw a trace of rainfall. Once the front moved through, high pressure settled in and brought sultry air from the Gulf of Mexico on the 6th. This made for the first real summer-like stretch of 2015, which lasted until the 10th. Temperatures above 80°F were common, and many locations were well into the 80s! As a result, numerous records fell.

The summer-like temperatures did fade for a return to spring weather into the middle of the month. A powerful cold front pushed through the Midwest on the 11th, bringing several lines of storms. Numerous trees and power lines were toppled in Indiana and Ohio. Tractor trailers also were knocked over between Indianapolis and Cincinnati, with a 59 mph wind gust observed at the Port Columbus Airport in Columbus, OH. A roller coaster ride of temperatures then ensued. From the 11th to the 14th, temperatures dropped into the 50s and 60s, then 80s returned in most places (save Chicago, which is often influenced by Lake Michigan this time of year) on the 17th and 18th.

A large and cold high pressure in the Northern Plains then funneled in a chilly air on the 20th. With temperatures near record cold levels, ice pellets even fell in Rockford, IL during the morning hours. This was the only time on record that traces of frozen precipitation fell this late into the year. In addition, Rockford also broke their record low maximum temperature for the date, at 47°F.

After this brief cold spell, spring returned in a big way. Severe weather capped off the last ten days of the month. On May 26th, a low pressure system from the Plains helped to set off numerous storms over the region.

Map of May 26, 2015 Storm Reports from the Storm Prediction Center (above)

In fact, an EF-0 tornado touched down near Summit, IL, just southwest of Chicago and a more powerful, EF-1 (winds of 87-110 mph) tornado impacted Greene, OH, just south of Dayton, damaging numerous cars and homes! (here's the video of the tornado). Over 100 severe wind reports were recorded as well, downing numerous trees and power lines. After a brief respite, more severe weather returned on the 30th. This time, it was confined to Ohio and Indiana, where an EF-1 tornado made a brief touchdown just southeast of Indianapolis. The tornado caused two cars to stack on top of one another, amongst other damage. Hail up to an inch in diameter was also seen as trees and power lines fell once again. Furthermore, a record 1.28” of rain fell in Indianapolis.

As for total May precipitation, most areas finished opposite of what occurred in April. The Chicago area was drier than average in April, however, May saw 4.66” of rain at Chicago O’Hare airport, almost an inch above the average of 3.68”. On the other hand, Indiana and Ohio were all had above average rainfall in April, but Dayton, Cincinnati and Indianapolis were anywhere from 2.50” – 3.50” below average in May! Temperatures were more uniform than the rainfall department, with all areas above average to finish out the month. Chicago and Rockford were above average by nearly 1.5°F, while Indianapolis on east into Ohio were 3.8° to 6.6° above average.

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