While the fall will kick off with days of sunshine and temperatures above normal in some Northeast cities, including New York City and Philadelphia, the polar vortex may make its return for short, sporadic periods this month, forecasts AccuWeather. “The vortex could slip at times, maybe even briefly in September for the Northeast,” AccuWeather lead long-range forecaster Paul Pastelok says. “There could be a significant shot of chilly air that comes across the Great Lakes region and into the interior Northeast sometime in mid- to late-September.”

Unlike the Northeast, the trend for the Northern Plains and northeastern Rockies will be more winter-like as early snow and cold air blast the area this fall, adds AccuWeather. While it’s not uncommon for this area of the country to receive snowfall in the fall, areas from Bismarck, N.D. to Miles City, Mont. will be more vulnerable to an increased number of snowstorms. Aside from the snow, temperatures are expected to be near or below normal for most of the region, with some parts of the southern Rockies experiencing temperatures 2°F to 4°F below normal.
As the cold grips areas from the Colorado Rockies to the Sierra, the cold may even expand southward into the Central Plains and portions of the Midwest, including Chicago and Milwaukee and Green Bay, Wis. But while the cold and snowy weather will create ideal early-season conditions for ski resorts and avid winter athletes in the eastern Rockies, the western Rockies will be a different story. “The dryness in the West is going to hamper any early significant snowfall in the western Rockies from Lake Tahoe to Bend, Ore.,” Pastelok comments.
With the heart of the hurricane season in the early fall, September is predicted to be an active month in the Atlantic, according to AccuWeather. As the Southeast coast, from Florida up through North Carolina, is most susceptible to a direct hit from a tropical system this fall, areas farther north, including Boston and New York City, could experience rain from a tropical system as well. Finally, the Southeast will feel the effects of El Niño with an increase in stormy weather and rain. Areas from New Orleans to Jackson, Miss. and Atlanta will see above-normal rainfall for the season, while areas closer to the southeastern coastline, such as Pensacola, Fla., will likely break both daily and perhaps even yearly rainfall records this fall due to the immense amount of rain that fell during spring.