Many parts of the eastern half of the country are facing a colder-than-usual May. But summer is not far away.
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Temperature-wise, it’s the calm before the storm.
After an early spring marked by rising and falling temperatures, forecasters expect much of May to be cooler than normal in most parts of the country, with the potential for a hot summer from coast to coast.
Brad Pugh, a meteorologist with the Climate Prediction Center, said the cooling will be most pronounced in the Midwest. Overnight lows could even dip into frost or sub-freezing territory in the region, he said.
Paul Pastelok, chief long-range expert at AccuWeather, said it will feel like early spring for most of the eastern half of the United States, at least for the first half of the month. During that time, there may be some sunny days, but “it’s likely to be cloudy during the day,” Pastelok said.
A notable exception to the cooling trend is the West Coast, particularly the Pacific Northwest, where temperatures are beginning to exceed average earlier. Pastelok said the temperature transition here will be much faster than in other parts of the country, and that warmth will spread from west to east throughout May as summer approaches.
“It’s going to be more like late March, early April than early May in the East…We still need jackets, we still need sweaters,” he said. “But in the Northwest, it’s time to put on your summer clothes.”
Cool May gives way to hot summer from coast to coast
Pastelok said the cooler temperatures in the eastern part of the country are due to a drop in the jet stream that lingers over the United States, where an atmospheric blockage prevents the jet stream from heading north toward Canada.
Once we get into about the third week of May, he said, that block will not be as strong and the cooler air will move away.
Average temperatures in May could be 2 to 4 degrees colder than normal in some major cities, including Detroit, Pittsburgh and New York City, Pastelok said. It may not sound like a big deal, but over a 30-day period, 2 to 4 degrees is a big difference from a typical May, he said.
He said daily temperatures in eastern cities could be up to 15 degrees cooler than average.
For example, in New York City, typical May temperatures range from the low 60s at the beginning of the month to the mid 70s at the end. But this year, temperatures are likely to stay in the 60s or low 50s, with lows dropping into the 40s.
Normal May high temperatures in Chicago are similarly in the 60s to mid-70s, Pastelok said, but the first half of May this year will be 10 to 15 degrees colder than average, with highs in the 50s. By mid-month, west-to-east warming will reach Chicago, with temperatures expected to be below normal or above normal by late May.
Pastelok said the transition to summer in the east will be much more gradual than in the west, with higher temperatures and humidity through June. He said that might be bad news for those looking to hit the pool early in June, but good news for those looking to relax by a bonfire in the evening.
The Climate Prediction Center’s outlook for May through July shows an overall trend towards a higher-than-normal chance, with a strong chance in the Northwest and some areas of the South and Mid-Atlantic.
“Our outlook for May, June and July increases the likelihood of above-average temperatures across much of the country,” Pugh said.
AccuWeather is predicting an “extreme summer of weather” with a heat wave in the West and South, frequent thunderstorms that pose a risk of flash flooding from Texas to the Ohio Valley, and worsening drought in the Northwest and Great Basin.
“This summer’s extreme weather could divide the country,” Pastelok said. “Drastically different conditions can occur simultaneously, with some regions experiencing flash flooding and others dealing with extreme heat, drought, and wildfires.”
May brings frost and can freeze in some areas
Temperatures in the Midwest, especially around the Great Lakes and upper Mississippi Valley, will likely be 5 to 10 degrees cooler than average during the first half of May, Pugh said. He said that on May 1st, early morning low temperatures in states such as Wisconsin reached freezing.
Pugh said another frost or freeze is possible from May 7th to 8th.
Pastelok said other areas that could get cold enough overnight include the mid-Atlantic coast and New England.
Above-normal temperatures are expected in the northwest from early morning.
Temperatures are already starting to rise in the West. Pastelok said cities like Spokane, Washington, east of the Cascade Mountains could experience several consecutive days of 10 to 15 degrees Celsius above average, and the warming would spread into Nevada, Utah, Arizona and California.
The high temperature in Spokane on May 3 is expected to be 80 degrees and May 4th 79 degrees.
The Great Basin region as far as Boise, Idaho, could see high temperatures in the 70s, 80s and even 90s for a few days by the end of May, Pastelok said. He said the Central Rockies didn’t have a lot of snow, but they dry out and heat up quickly as summer gets into full swing, making it “very dangerous during fire season.”
“In some cases, it feels more like late June than early May,” Pastelok said, adding that many heat records could be broken in the Northwest as summer begins.
