Nearly 25 million people in the U.S. are under a frost warning

(CNN) — Most freeze warnings across the southeastern United States have been updated by local National Weather Service offices to include a freeze warning (NWSIts abbreviation in English), which stretches from Texas to North Carolina.

The warnings now cover nearly 25 million people and stretch from Longview, Texas to Sanford, North Carolina.

Freeze warnings go into effect this Monday night and last until Tuesday morning.

Snow watches and advisories have been issued further south for parts of Louisiana, Mississippi, Alabama and Georgia.

Crop damage

Temperatures across the southeastern United States will be below normal for this time of year on Tuesday morning. Temperatures are expected to drop to -6°C to -1°C Tuesday morning in Atlanta, Charlotte and Birmingham, Alabama, putting crops at risk.

“Snow and freezing conditions can kill crops and other sensitive plants, and damage unprotected outdoor plumbing,” warns the Peachtree City, Georgia, NWS office.

Keeping plants indoors is an easy way to protect them from hard frosts, but if you can't do that, covering them can also help.

For a farmer, recovering his harvest may be a little more difficult.

As the warmest winter on record in the US comes to an end, fruits and trees have been in bloom for weeks. An exceptionally warm winter sends premature signals for crops to start germinating early. When a timely frost occurs in March, these crops are exposed and vulnerable to frost damage and frostbite.

Farmers use tarps, irrigation and large fans to cover their crops as much as possible to prevent damage.

This cold snap means cities in the Midwest, South and East Coast will experience warmer temperatures in January and February than are typically felt in early March.

St. Louis could see a swing of more than 6 degrees from 15 degrees Celsius on Saturday to 4 degrees Celsius this Monday. Atlanta's high temperature could drop 10 degrees Saturday through Monday: 21°C to 10°C.

These temperatures are not freezing, but in parts of the South they are more common in mid-winter.

Memphis, Tennessee, and Huntsville, Alabama, are forecast to see highs of 10°C on Monday, a typical mid-January high.

Philadelphia's maximum temperature on Tuesday will be 7°C, its average high on February 19.