Hot May may not foretell coming summer

The last 60 days have been amazing. The Miami Valley went from the third-coldest April on record to the second-warmest May.

These records go back to 1896. The average temperature for Dayton in April was 45.9 degrees, which was nearly six degrees below normal. In May, the average temperature soared to 70.5 degrees, jumping 9.1 degrees above normal.

This major temperature swing occurred thanks to a blocking weather pattern that developed over Greenland late in March and lasted through most of April. This pattern forced the jet stream to stay unusually far south through the majority of the month. Cold, Canadian air kept flowing into the Miami Valley, bringing with it bouts of snow late into the month.

The major pattern change occurred the last few days of April as the block across Greenland released, allowing the jet stream to return to a more typical flow pattern around the arctic circle. As this Greenland block was breaking down, an unusually strong area of high pressure developed off the Mid-Atlantic coastline. Since the wind typically flows clockwise around high pressure, southerly winds began to become dominant across the eastern half of the country.

This allowed winter to almost turn to summer across the Miami Valley.

Instead of temperatures climbing into the 60s and 70s, we saw readings soar into the 80s and 90s. On May 27 and May 28, the temperature in Dayton reached 90 degrees for the first time in

more than 240 days — and were the first consecutive 90-degree days since September 2016.

The big question a lot of people have been asking is whether we will have a hot summer. The answer may not be as clear-cut as one might think.

The weather pattern seems to be setting up to be more active as we head into the summer. This means better chances for rain and storms. When the weather is more active, it can prevent major heat waves from occurring. It is very difficult to heat surface temperatures above 90 degrees when the top layer or two of soil contain quite a bit of moisture. Typically, our hotter days occur when we have a lack of rainfall. Not surprisingly, May turned out to have below-normal levels of precipitation.

The latest summer outlook from the Climate Prediction Center (CPC) is calling for near- to slightly above-normal temperatures through the summer. However, the CPC is also calling for above-average precipitation.

A more active weather pattern may keep us from having too many 90-degree days. However, if we start to dry out, expect the temperature to climb. If the pattern does stay active, this may increase our risk for severe storms this summer.

It certainly looks like we’ll have plenty to look out for over the coming few months.