Colder Pattern to Kick Off October With Potential Frost and Freeze in the Midwest, East

 Jonathan Erdman 

Published: September 25, 2020

A much chillier weather pattern will plunge into the Midwest, East and South next week, bringing with it the potential for frost and freeze conditions as the calendar turns to October.

The autumnal equinox officially kicked off fall in the Northern Hemisphere this past Tuesday, and as the calendar is about to change to October next week, it should also feel like fall in much of the eastern half of the nation.

This change will be driven by an abrupt shift in the jet stream, which will take a sharp southward nosedive over the central and eastern U.S. in response to a pair of high pressure systems bulging north over western North America and the western Atlantic Ocean.

This jet stream nosedive will tap chillier air from Canada and pull it through much of the central, southern and eastern U.S. At the same time, it will bring drier and hotter weather to the fire-fatigued West.

This pattern may hold into the first weekend of October, and perhaps sometime after that.

High/Lowlights

There should be a pair of cold fronts that will usher in this chillier pattern next week.

The first should sweep into the Plains and upper Midwest this weekend, then into the South Monday.

A second, potent cold front arrives into the Northern Plains around mid-week, then quickly plunges through the South later next week. Afterward, daytime highs may struggle to rise out of the 40s in the northern Great Lakes, 50s in much of the rest of the Midwest and 60s as far south as the Tennessee Valley and parts of the Carolinas later next week.

(MAPS: 10-Day U.S. Forecast Highs/Lows)

Morning lows later next week could plunge into the 30s in the northern and central Plains, parts of the Midwest, and even in a few of the coldest spots of the Appalachians. Some of these areas could see their first frost or freeze of the season later next week.

Lows in the 40s are possible into the Tennessee Valley, parts of the Carolinas and southern Plains.

(MORE: The Earliest You Could See a Freeze in Your Area)

Lake-Effect Flakes?

There's one other interesting facet to this chillier pattern next week.

Water temperatures over the Great Lakes are usually at their warmest as fall begins because of a summer's worth of heating.

So colder air flowing over these relatively warm bodies of water will generate bands of lake-effect precipitation, primarily rain, next week.

The larger the difference between the cold air and warmer lake, the more vigorous the lake-effect precipitation.

In next week's case, there could be lake-effect thunderstorms, perhaps even some waterspouts, given the air-lake temperature difference and the strength of spin in the atmosphere, or what meteorologists refer to as vorticity.

(MORE: October-December Temperature Outlook)

The setup for lake-effect rainbands next week in the Great Lakes. A few wet snowflakes could also fall in the northern Great Lakes.

Parts of the northern Great Lakes could even see a few first snowflakes of the season mix in behind the second cold front later next week.

If this happens, it would primarily be away from the warmer lakeshore over the interior of Michigan's Upper Peninsula, extreme northern Wisconsin or perhaps the Arrowhead of Minnesota.

Quite the way to usher in October, right?

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.