Fall Outlook: Chilly in the North; Mild in the Southeast, West

August 19,2016
The September through November months are expected to feature cooler-than-average temperatures across the northern tier of states, according to a fall temperature outlook by The Weather Company, an IBM Business.
Near to slightly above-average temperatures will prevail across the East Coast, South and much of the West, however, said Dr. Todd Crawford, chief meteorologist with The Weather Company.
According to Crawford, the September forecast is cooler across the central U.S. and into parts of the East. As of mid-August, the weather pattern that will bring these cooler temperatures has already begun to take shape.
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Tropical activity in the western Pacific has transported warm air into the higher latitudes, helping build a ridge of high pressure (bulge in the jet stream) aloft from eastern Siberia to the North Pacific. The ridge will occasionally nudge into the Pacific Northwest in early September.
This pattern favors a trough (dip in the jet stream) across the central U.S. that will allow cool air to drop down from Canada.
The cooling will progress eastward to the Great Lakes and Ohio Valley regions. At the same time, September will begin with warmer-than-average temperatures across the Pacific Northwest, but the warmth will gradually relax later in the month.
Much of the Southwest, including California, will see above-average temperatures during September.
(MORE: July 2016 Was Earth's Warmest Month on Record)

September Temperature Forecast

October-November Outlook

According to Dr. Crawford, a weak La Niña (cooler-than-average waters off the west coast of South America) should be in play through the fall and winter months. At the same time, warmer-than-average water temperatures will prevail across much of the North Pacific.
One fall and winter season that featured similar conditions was 1995-96, so the updated fall temperature outlook was based on what occurred then. That season was particularly cold during late fall and into winter, but Dr. Crawford indicated that there was considerable atmospheric blocking in the higher latitudes (strong high-pressure ridges).
This was at least partially a result of low sunspot activity, also known as a solar minimum. Since this won't be the case during the upcoming months, the current temperature forecast was tempered from what occurred in the 1995-96 season.

September-November Temperature Forecast

October
Northeast: Warmer than average
Southeast: Slightly warmer than average
North Central: Cooler than average Plains; near to slightly warmer than average in the upper Midwest
South Central: Slightly warmer than average
Northwest: Cooler than average
Southwest: Near to slightly warmer than average
November
Northeast: Cooler than average
Southeast: Near to slightly warmer than average
North Central: Cooler than average
South Central: Warmer than average
Northwest: Cooler than average Washington to Montana, near to slightly above average elsewhere
Southwest: Near average
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