The La Niña that has driven the extreme weather since winter is over, but the lingering effects mean no summer for the Great Lakes, drought conditions expanding out of the southern Plains, and flooding expanding into the Midwest from the Mississippi Valley.
The weather pattern that produced a wild winter for the Northeast and parts of the Midwest, then extreme flooding and devastating killer tornadoes this spring, is changing to one that may not be as volatile this summer. However, given the national economic impacts of the tornadoes and floods this spring, all it would take is one hit by a major hurricane to stress the economy even more.
Senior Meteorologist Paul Pastelok, leader of the AccuWeather.com Long-Range Forecasting Team, said a change in the weather pattern means areas of the lower Mississippi Valley hit by flooding will have hot, drier weather this summer, which could help clear standing water and dry saturated ground.
However, we will need to keep a careful eye on the tropics as late-season tropical storms could threaten the Gulf and/or East Coast states.
The end of the La Niña pattern will threaten to make the Great Lakes/Ohio Valley/Midwest a region "without a summer." Repeated intrusions of cool air from Canada, along with showers and thunderstorms, will keep temperatures below normal in many areas. Temperatures topping 90 F may be rare.
The severe weather that has plagued the South this spring will shift northward. Frequent bouts of thunderstorms could mean numerous instances of flooding, hail and wind damage, even tornadoes. While we probably had the most extreme tornado activity of 2011 during April and May, the summer still has potential to bring a few moderate outbreaks of tornadoes.
Flooding may be the biggest concern this summer, as already-soggy ground canhandle only so much heavy rain.
The Northeast has been frequently cloudy and damp this spring, but that is forecast to change this summer. While not as hot as it was last year, it will become warmer and more humid this summer with temperatures close to long-term averages.
That means in major cities along the I-95 corridor, temperatures will hit the 90-degree mark or higher for the typical number of times this summer. The summer may end with good beach weather after a dismal start on Memorial Day weekend.
The region will have its share of rainfall, as more showers and thunderstorms will return during mid-summer, and humidity levels may run higher than normal.
Pastelok also added there is always the threat of a tropical system sneaking up the coast from the south, as hurricane season will ramp up by the end of June.
Hot, dry in Southeast
After the pattern change, the Southeast will remain hot and dry into the early summer with a high fire danger.
As the season progresses, increasing amounts of thunderstorms, and perhaps tropical systems, could bring some relief from the heat and dryness, but would increase the threat of flooding.
"Areas from the Middle Atlantic on south and west will run with temperatures above normal, but not as warm as last year," Pastelok said. "The dryness in the Southeast will continue into the start of summer."
Pastelok said the chance for 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 some very beneficial rainfall to the area. However, there is always the chance a system could develop into a hurricane.
The Southwestern Plains into the Southwest Deserts will remain hot and dry for much of the summer, which could mean an increased chance of wildfires.
"The drought in the Southwestern Plains and interior Southwest will continue, spreading northward into the central Rockies," Pastelok said. "As always, with this drought comes a high fire danger."
The monsoon season that was non-existent last year may be more robust this summer, according to Western Expert Meteorologist Ken Clark, 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.
“June Gloom" might get a late start this summer, but could persist well into the summer along the California beaches. 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, including beach areas, a persistent chill.
"The West Coast will have near- or below-normal temperatures as the cold (ocean temperatures) hang on through the summer, while the interior West heats up," Pastelok said. As for the Pacific Northwest, the region will be back and forth, with some drying late in the season.