Persistent Fall Pattern for the Midwest

We've already seen several bouts of cool air invade the central and eastern states over the last few weeks, reminding us that the official start of fall is right around the corner. Last week, many cities recorded their coolest morning temperatures since May or early June.

This week, a very fall-like weather pattern will engulf many states in the Midwest and East. Good news for those that would like to see the fall colors take over.

(MORE: Fall foliage report | Fall allergies)

Persistent Trough in Jet Stream

The culprit for the cool pattern is what meteorologists call a "trough", which is basically a large-scale dip in the jet stream that allows Canadian air to dive southward into the United States.

Some of these so-called "troughs" are progressive and move along quickly, allowing temperatures to rebound. In this case, the trough will get reinforced later in the week/weekend, keeping the fall temperature regime in place.

If this were January, we'd be shivering and your furnace would be working overtime. But since it's September, we get to enjoy the temperatures, particularly after enduring the third hottest summer on record in the lower 48 United States.

Forecast Ahead

The core of the coolest temperatures will be centered on the Upper Midwest and Great Lakes.

Lows in the 30s and 40s will be common from the Great Lakes to the Ohio Valley on Wednesday morning. Chicago and Detroit will be within a few degrees of daily record lows.

(MAP: Average first freeze)

Though temperatures may rebound some in the Plains and Midwest Wednesday and Thursday, another push of cooler air is likely by late week. Our high temperature forecast map for the first day of fall on Saturday is similar to what we will see on Tuesday, indicating how persistent the cool pattern will be.

You can track the changing temperatures using the high and low temperature forecast map links below or use this link to access your ten-day forecast.

(HIGHS: Tue | Wed | Thu | Fri)

(LOWS: Tue | Wed | Thu | Fri)