Fall is about to descend, according to Planalytics Inc., so retailers should begin seeing increased movement of their autumnal merchandise. Although some regions of the United States have felt the first bit of chill in the air this week, next week will see more definitive cooling.

The retail weather forecasting firm said that, beginning Tuesday, consumers east of the Rockies will need a coat to wear and something warm to drink.  By Tuesday and Wednesday, September 18 and 19, consumers may be dealing with a 25 to 30 degree Fahrenheit decrease in temperature during the day and overnight compared to recent weeks. The temperature tumble should be felt across the Northern Plains and Western Great Lakes, with frost likely across regions including the major population areas of Minneapolis, Green Bay, Madison and Milwaukee, Planalytics noted.

The Central Plains and Ohio Valley are also likely to experience a daytime dip, bringing them back to seasonal temperatures. Chicago and St. Louis will experience overnight lows in the 40s, a departure from last week’s conditions, when those city’s populations enjoyed nightly temperatures in the 70s.  The cool trend will spread into the Northeast, which will experience a temperatures drop below normal for mid to late September.

Temperatures rebound slightly late next week, Planalytics noted, but a second, more sustained cool down moves back in for the official start of autumn on Saturday, September 22.