The phrase "April showers" couldn’t have been more fitting in April 2015 for the Midwest. The month left winter in the dust for the most part, with an abundance of warmth, rain, and even bouts of intense severe weather. Though Indianapolis saw a trace of snowfall on the 8th and the Chicago area had the same on the 22nd, these events were just minor blips in a month characterized by traditional spring weather.
As the title foreshadows, April was relatively warm for the Midwest. The first two-thirds of the month ran generally above average and the region endured multiple rain storms and rounds of severe weather. First, a system on April 2-3 dumped a mind-boggling 2.19" of rain on Cincinnati, contributing to more than 40% of its monthly precipitation total. Columbus and Dayton saw upward of 0.75-1.00", with less in Indianapolis and Chicago.
Above: Map of severe storm reports on April 9th, 2015 from the Storm Prediction Center
Next, a low pressure system and its associated cold front between the 6th and 10th provided devastating severe weather in Illinois and heavy rain across the Ohio Valley. After a stationary boundary brought showers and periods of rain on the 6th and 7th, temperatures warmed into the 70s to around 80° ahead of the cold front on the 9th. While the frontal passage brought strong storms with damaging winds and hail to areas of Indiana and Ohio, Chicago and northern Illinois saw the worst. Not only did storms produce severe winds and hail, but they also spawned strong tornadoes, one of which was an EF-4 (166 - 200 mph winds) in Lee County (see aftermath from Fairdale). When all was said and done, the region received upwards of 1 - 2 inches of rain, most of which fell from April 8th to the 10th. The image above from the Storm Prediction Center shows a concentration of severe storm reports from Illinois through Ohio on April 9th.
On April 19-20th, a low pressure system brought yet another widespread rain event to the Great Lakes and Ohio Valley. This time around, areas from Indianapolis east into Ohio were the big winners, receiving 0.70-1.30 inches of rain. Following this system, a noticeable pattern change took shape across the Midwest. While warmth reigned the first 20 days of the month, below average temperatures finished out the month. The period from the 22nd to the 24th was particularly chilly featuring temperatures 10 and 15° below normal. In fact, Chicago only reached a high of 46° on April 22nd (with some snow showers!) with Dayton, OH just hitting 48°. The graph below shows Indianapolis' average temperatures for April compared to normal, which summarizes the month's temperature pattern well. Albeit chilly, the final days of the month ended quietly.
In the end, the monthly temperatures for April 2015 finished 1 – 3° above average for the region as a whole. Precipitation ran the same way, with a rainfall surplus for Indianapolis through the major cities of Ohio. Chicago actually followed suit with March (although not to the same extreme) and ended with below average rainfall. The graph below shows precipitation amounts across the region.
