CNN
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A dramatic pattern shift is bringing the coldest air since spring to millions of people in the central and eastern United States, helping areas that have struggled to get rid of lingering heat it feels more like November than October.

Since the season started last month, it has been difficult for much of the country to experience extended periods of autumn cold. But the combination of an extended cold front and an incoming cold Canadian airflow will change that and temperatures could drop to 10 to 15 degrees below average by midweek.

As of Tuesday morning, more than 60 million people, from the Plains to the Appalachians and the Northeast, are under some form of freeze or freeze warning as temperatures drop.

The first aspect of this cooling – a far-reaching cold front – started this weekend. This cold front moved from the northern and central US through the eastern half of the US on Monday, ushering in a real autumn chill for some along the way. Even the colder air from Canada will be pushed much further south throughout Tuesday and Wednesday.

Tuesday could be the coldest day of the week in Chicago, where high temperatures could struggle to reach the 50s. Before Monday’s high of 57, Chicago had not recorded a high in the 50s since April.

Temperatures will drop again in many areas outside the Midwest on Wednesday. Wednesday is likely to be the coolest day since spring for millions of people, and in many locations it will feel more like late November than October.

“Really fall-like weather is forecast … through the start of the weekend” further south, the National Weather Service in Atlanta said Monday.

High temperatures in Washington, D.C., could top out in the mid-50s on Wednesday — 10 to 15 degrees lower than normal for mid-October.

Atlanta could struggle to get into the low 60s on Wednesday and stay in the 60s through Friday. The city hasn’t had high temperatures below 70 degrees since May, and this time of year temperatures are typically around 75 degrees.

Wednesday will also be the coldest day of the week for much of the Northeast, with highs in the 40s and 50s for many. Because daytime temperatures are so chilly, there is room for nighttime temperatures to potentially dip below freezing. Given the cold, a few snow showers could dust the highest elevations from West Virginia to New York and New England on Tuesday evening.

“Frost and freezing conditions are likely for several nights and in many areas this week,” the National Weather Service in State College, Pennsylvania, warned Monday.

Frost and freeze warnings are active for millions of people this week and more could follow in the coming days.

Freezing conditions can kill plants left unprotected from the cold or end the growing season for some regional staple crops. These conditions are also dangerous for anyone who does not have access to adequate heating.

In western North Carolina, which was devastated by Helene late last month, freezing or near-freezing temperatures are possible every night Tuesday through Thursday.

By the end of this week, temperatures will drop back to more typical October conditions across much of the central U.S. and the Northeast. The cold will continue through at least Friday in areas further south, such as the southern Appalachians and the Southeast.

More seasonal highs in the 70s and 80s return for the Southeast on Saturday, while the 60s and 70s will be common north into the Midwest and parts of the Northeast.