Forecasters say the autumn weather preview earlier this week was just that, a glimpse into what's to come. A burst of chilly air will sweep from northern Canada through the north-central United States late this week and into the Northeast this weekend, bringing not only a dose of sweater and flannel weather but also some frosty consequences.
Those hoping for fall weather like that which has been sampled in recent days are in luck, but temperatures are likely to trend even lower than those felt far this season in many areas.
Even though the chilly air will pale in comparison to the blast that left people shivering in the Rockies and High Plains along with a snowfall early in September, some of the chilliest air of the season is forecast from the Upper Midwest to the Northeast in the coming days and can bring temperatures as low as 20 degrees below average.
Low temperatures this time of year typically range from the lower to middle 40s F across the northern tier to the lower 60s over the central Plains and the mid-Atlantic coast to the middle 60s over the interior South.
Temperatures could challenge record lows for the date in northern portions of Minnesota, Wisconsin and Michigan prior to the end of the week. A freeze is forecast for International Falls, Minnesota; Ironwood, Wisconsin; and Houghton Lake, Michigan; with low temperatures ranging from the middle 20s to the lower 30s F. The low temperatures are 10-20 degrees below average for the middle of September.
The crisp, cool air will be felt farther to the south as well with low temperatures forecast to be in the 50s during the latter part of this week in St. Louis and Kansas City, Missouri, and Omaha, Nebraska.
Low temperatures in the 40s will be common in Detroit, around the Chicago suburbs, much of the Ohio Valley and the northern and western suburbs of the major Interstate-95 cities from Richmond, Virginia, to Washington, D.C., Philadelphia and New York City. Boston will slip into the 40s during some nights this weekend while temperatures stop in the lower 50s farther southwest along the I-95 zone through eastern Virginia.
Frost is not expected in the large cities and metro areas that surround them in the Midwest and Northeast. However, in portions of the central Appalachians and interior New England, there will be the risk of a killing frost in the rural areas during Friday night and Saturday night with low temperatures forecast to be near the 32-degree mark and even a tad lower in some cases.
Summer harvesting may need to be accelerated to avoid losses, and gardeners may want to protect sensitive flowers or bring them indoors to preserve their longevity.
The upcoming heavy frost follows a touch of light frost from early in the week in parts of the central Appalachians.
Patchy cloud cover may be enough to prevent a frost on one or more nights over the interior Northeast, but there is no guarantee the clouds will hold through the night.
The frosty conditions could also accelerate the process of leaves changing colors in some areas.
As temperatures sink to chilly levels at night, fog is likely to develop in the river valleys and limit visibility enough to slow travel for a few hours during the late-night and early-morning hours.
And it won't be crisp just during the night. Daytime highs have already been suppressed in recent days due to high-level smoke from Western U.S. wildfires dimming the sun's intensity.
As steering winds cause the smoky air aloft to drop southward, the origins of the air alone will create cool conditions during the daytime, even where the sun shines brightly overhead.
At the peak of the cool air, highs will be in the 50s across the northern tier to end this week and could be held to the upper 40s over the higher elevations of the Northeast this weekend.
Highs are forecast to be in the lower to middle 60s around Chicago and New York City. The temperature could struggle to top 70 in Atlanta late this weekend to early next week as the cool air settles into much of the Southeastern states.
The push of chilly air will follow rain from Sally in the Southeast and along the mid-Atlantic coast to end this week. There are indications that the cool weather pattern will hold in much of the Eastern states into next week with the potential for Hurricane Teddy to continue to drift northwest of Bermuda and possibly approach northern New England or Atlantic Canada at some point.