Generally speaking, the fall outlook indicates a pronounced, southward shift of the jet stream, and over the mid-to-late portion of the season the formation of a U-shaped buckling all the way to the southern Plains, and at times extending to Eastern seaboard. This in turn should allow for frequent cool to cold air intrusions and a general trend in temperatures to below- and at times much below-normal average.
Northwest and West
The Pacific Northwest and the northern Rockies will see the return of an upper air pattern that generates wet, at times no worse than seasonal cold. Look for frequent outbreaks of cold early on, followed by moderate to more seasonal readings in all but the eastern slopes of the northern Rockies.
Weather starts rather docile very early on into the fall season on the northern and central Plains, although a frequency of features marching across Dakotas, along with bouts of early-season cold, may lead to further development issues and harvest delays. Deeper into the fall, rather challenging periods of weather are ahead, including wide temperature swings.
Early in the season, periodic of spells of cooler-than-average temperatures are expected across the Southeast and mid-Atlantic region; due somewhat in part to tropical systems tracking northward across the Eastern States or the western Atlantic that in turn buckles the jet stream southward allowing cooler air to follow-in behind. Meanwhile, from Texas, east-northeast through the mid-South and at times the mid-Atlantic region, mild, late Summer-like warm episodes early in the season will yield to more seasonal readings.
As for the Northeast and New England, the area will continue in the midst of an active pattern, aided by tropical systems making their turn into the northwestern Atlantic. This is turn allows lobes of cool air to settle southward. Early-season frosts and light freezes are possible. Thereafter, a rather broad southwest flow aloft will occur frequently, allowing spells of frequently milder-than-usual weather to dominate.
Across the Midwest and Great Lakes Corn Belt, a challenging mid- to late-fall weather pattern is expected, but not before a mild to warm start and extended dry spell very early in the season. Cold air outbreaks will be few and far between until then. This, however, will not be rule advancing deeper into the season. Temperatures will build to a range of below-normal to well-below normal, but with some fluctuations from the lower Great Lakes to the Ohio Valley. Several early winter-like cold wave episodes are likely.
Soulje is an agricultural meteorologist who writes from Illinois.