While the first day of Autumn 2015 will bring seasonable temperatures in much of the Midwest and Northeast, above-average warmth will make a comeback as September comes to a close.
According to AccuWeather Long-Range Meteorologist Ben Noll, "Despite a step down with temperatures following the last official weekend of summer, no big blasts of Canadian air will chill the Midwest and Northeast for much of the upcoming week."
Autumn officially arrives at 4:21 a.m. EDT on Wednesday, Sept. 23.
Tens of millions of people from the Midwest to the Northeast may need a pair of sunglasses to enjoy the first day of autumn in 2015.
It will look and generally feel like fall from the middle Mississippi Valley to the central and northern Appalachians from the aspect of low humidity and bright sunshine, following patchy early morning fog on Wednesday.
Over the northern Plains and the upper Great Lakes region, following the departure of clouds, showers and thunderstorms from Tuesday, warmth will build during the middle of the week.
Clouds are likely to be on the retreat in much of the coastal Northeast during Wednesday, including for the pope's visit. This is provided a series of storms remain offshore in the Atlantic.
The vast majority of the region from Chicago, Detroit and Indianapolis to Washington, D.C., New York City and Boston will have highs in the 70s F for the middle of the week.
"Looking ahead, while the pattern is not likely to deliver many more 80-degree days in the Northeast, warm weather fans cannot ask for much better weather for the latter part of September and the first part of October," Noll said.
Noll is referring to temperatures forecast to run 5-15 degrees above average in the Northeast for late September and early October. Even greater positive departures can occur in the Midwest.
Throughout the Midwest and Northeast, normal average temperatures trend downward by a degree every two to three days. For example, in cities along Interstate 80, a high of 75 may be near average for the middle of September, but 5-10 degrees above average during the first week of October.
There may be one attempt at some chilly frosty air dipping into part of the Northeast late next weekend.
"Northern potions of upstate New York and New England may get a frost, but there is little or no chance of frosty conditions farther to the south and west before the end of September," Noll said.
Where the frost fails to visit before leaves cascade to the ground, the prospect of bright fall foliage may suffer.
Allergy sufferers in the Midwest and much of the Northeast will have to endure ragweed and grass pollen a while longer.
No major storms are likely to affect areas from the Midwest to the Northeast into early October.
"We are likely to have high pressure areas hold on or rebuild into early October, as they have done from the southern Plains to New England during much of September ," Noll said. "One area that is likely to be rainy and unsettled is Florida and vicinity."
In the southeast corner of the nation, a mix of tropical moisture and slow-moving storms originating from the western Caribbean, the eastern Gulf of Mexico and the nearby Atlantic Ocean could bring locally heavy rain.
Where clouds and rain persist in the Southeast states, temperatures may average below normal.
At times, the leading edge of the southern moisture can reach into part of the mid-Atlantic with a couple of bouts of rain.