The La Nina that drove extreme weather since winter is winding down, according to AccuWeather forecasters. However, the lingering effects will mean no summer for the Great Lakes, drought conditions expanding out of the southern Plains, and flooding into the Midwest from the Mississippi Valley, they say.
The weather pattern that produced a wild winter for the Northeast and parts of the Midwest, then extreme flooding and devastating tornadoes this spring is changing to a less volatile one this summer.
Paul Pastelok, senior meteorologist and head of AccuWeather.com long-range forecasting team, says a change in the weather pattern means the lower Mississippi Valley areas hit by flooding will have hot, dry summer weather, which could help dry saturated ground. “However, we will need to keep a careful eye on the tropics as late-season storms could threaten the Gulf and/or East Coast states,” he adds.
As La Nina wraps up, the Great Lakes, Ohio Valley and Midwest could become a region "without a summer." Cool air from Canada along with showers and thunderstorms will keep temperatures below normal in many areas, and 90 F temperatures may be rare, Pastelok notes.
Elwynn Taylor, Iowa State University climatologist, expects summer in the Midwest to be one of extremes. He sees temperature patterns unfolding as “a cooler-than-usual week or two, and then a warmer-than-usual week or two.” Samples of such roller-coaster temperatures have surfaced in May as a week with lows in the 30s F followed with a few days with highs near 90 F
Frequent bouts of thunderstorms could mean flooding, hail and wind damage, even tornadoes. While this year’s most extreme tornado activity likely will have occurred in April and May, the summer could still produce a few moderate tornado outbreaks, he says.
Flooding may be the biggest concern this summer, as already-soggy ground can handle only so much heavy rain.
The Northeast has been cloudy and damp this spring, but that’s forecast to change this summer. Projections place temperatures close to long-term averages, which means in major cities along the I-95 corridor will hit 90 F or higher for the typical number of times this summer. The region will have substantial rainfall, as more midsummer showers and thunderstorms will return, and humidity levels will exceed normal levels.
Pastelok adds there’s always the threat of a tropical system moving up the coast from the south, as hurricane season gets underway by late June.
The Southeast will remain hot and dry into early summer with a high fire risk. As the season progresses, more thunderstorms, and possible tropical systems, could offer relief from the heat and dryness, but would increase flooding.
"Areas from the Middle Atlantic on south and west face above-normal temperatures," Pastelok says. "Dryness in the Southeast will continue into early summer."
Early season (June) tropical storm development is possible along the entire Southeast U.S. coast. If the systems are weak and non-destructive, tropical moisture could bring beneficial rainfall to the area, Pastelok says.
The southwestern Plains into the Southwest Deserts will remain hot and dry for much of the summer. "The drought in the southwestern Plains and interior Southwest will continue, spreading northward into the central Rockies," he adds, which again, raises the fire risk.
The monsoon season may be more robust this summer, according to Ken Clark, AccuWeather’s Western expert neteorologist, which means thunderstorms over the Southwest. Clark suspects this will be a more active tropical season in the Eastern Pacific, especially in late summer. Weakening Pacific tropical systems could send tropical moisture into the Southwest and trigger thunderstorm activity.
Although La Nina is weakening and transitioning to a more neutral state, Pacific Ocean waters will still be colder than normal, giving the extreme West Coast a persistent chill. "The West Coast will have near- or below-normal temperatures as the cold [ocean temperatures] hangs on through the summer, while the interior West heats up," Pastelok notes.
As for the Pacific Northwest, the region can expect to be dry this summer.