Right on cue: Cooler air to sweep across East as fall officially begins

AccuWeather meteorologists say that the coolest push of air since late spring will have many locations in the eastern United States feeling like fall almost right on cue as autumn officially begins on Wednesday, Sept. 22.

Heavy rain and rounds of thunderstorms will signal the beginning of the pattern change in the region. Rainfall amounts could be significant enough to cause flooding problems in the Eastern states, and some rain will linger into Friday across parts of the Northeast. All of that rain will be associated with the same batch of air from Canada that brought freezing conditions and even some summer snow to parts of the Rockies early this week.

The decrease in temperatures won't be enough to cause so much as a frost on any pumpkins -- but a chill in the air will be noticeable given the above-normal temperatures in many places recently. And across the Midwest, temperatures will continue to plummet through midweek, with high temperature readings changing by as much as 20 degrees from one day to the next.

Following a couple of days with highs in the upper 80s in St. Louis, temperatures failed to reach 70 Tuesday afternoon. The same push of cooler air has reached Chicago as well, where temperatures were limited to the 60s on Tuesday just a couple of days after the mercury approached 90 -- and hit 89 -- Sunday.

The much cooler air is forecast to continue its eastward march through the end of this week.

In Nashville, Tennessee, highs in the low 80s on Tuesday will be swapped with highs within a few degrees of 70 both Wednesday and Thursday.

Around Detroit, high temperatures in the lower 80s from Monday will be replaced with highs in the 50s Wednesday and Thursday with clouds and drenching rain playing a major role. The rain may be heavy enough to lead to flooding problems from part of southern Michigan to Pennsylvania, New York state and New Jersey prior to the end of this week.

The biggest change in the Eastern states is likely to be with nighttime temperatures, AccuWeather Senior Meteorologist Brett Anderson said.

From late Thursday night to early Friday morning, cities such as Nashville; Birmingham, Alabama; Jackson, Mississippi; New Orleans; Charlotte, North Carolina; and Atlanta are likely to experience their lowest temperatures since May 15.

"Nighttime temperatures are predicted to drop into the low to mid-60s in New Orleans, which will finally provide some comfort for those working on cleaning up and rebuilding after Hurricane Ida's wrath in August," Anderson said.

Low temperatures are forecast to be in the middle 50s in Atlanta and Charlotte and dip into the 40s in Nashville -- a true sign that fall has indeed arrived.

While the cool air will stop short of sweeping southward through the Florida Peninsula, it will make progress through the central Appalachians, the mid-Atlantic and New England following heavy rain and flooding concerns from Wednesday to Friday.

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In the central Appalachians, the lowest temperatures since the middle of June are forecast, when chilly snaps sent temperatures down into the 40s and even the 30s in some locations.

The incoming airmass is not likely to send temps plunging to the point where a frost or freeze will occur, but it will definitely deliver conditions chilly enough to prompt many to break out the long sleeves. Jackets and a fleece could even be in order for some people.

"In parts of the Midwest, South and East Coast, where air conditioners have been running constantly since June, this will offer an opportunity to give those units a rest, ease electric bills and open the windows to let in some fresh autumn air," Anderson said.

Low temperatures in the 50s are anticipated in Washington, D.C., Philadelphia and New York City by this weekend.

The last time the temperature dipped into the mid-50s in Washington, D.C., was on June 23 when the low bottomed out at 55. In many cases, temperatures have not been this low on a widespread scale since the middle of June or earlier. If temperatures dip lower than that mark, it will be the coolest weather since the last couple of days of May, when a low of 50 occurred.

Highs in the 70s will be common, not only in the Interstate 95 corridor of the Northeast, but also in many areas of the interior South. When combined with low humidity, the crispness of the air and/or blue sky overhead in many cases will make it feel fitting for high school, college and professional football this weekend.

Even though a frost is unlikely to occur over the crisp first weekend of fall, another common autumn visitor may occur in parts of the East.

"Given the lengthening nights this time of the year, combined with a moist landscape after the recent big rain and light winds, it's a prime recipe for fog to form, which can hinder travel for several hours during the start of the day during Friday and Saturday," Anderson said.

FILE - In this Sept. 28, 2014, file photo, fog sits in the valleys of the White Mountains as leaves change colors, in this photo taken from Milan Hill in Milan, N.H. (AP Photo/Jim Cole, File)

Fog could be most common from the Tennesse and Ohio valleys to the Northeast, forecasters say.

Once rain swings through by the end of the week, it may come back for a brief encore in parts of the Northeast and Midwest on a toned-down scale this weekend.

There is a chance that a brief period of rain will swing northward and affect parts of the mid-Atlantic and New England for a time early this weekend. Similarly, a reinforcing pocket of cool air may trigger showers during part of the weekend around the Great Lakes. A dry weekend is foreseen for much of the Eastern states, with the lone exception being some lingering showers and thunderstorms for parts of Florida.

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