The National Weather Service calls an overnight freeze warning across south Mississippi and in some Louisiana parishes north of Lake Pontchartrain.
It says people should expect four to five hours of temperatures that can kill crops and other sensitive vegetation, as clear skies, light winds and dry air cover the area. Animals should also get extra protection.
The intense cold was predicted to start after midnight and continue until 7 a.m. - an hour or two after sunrise.
In Mississippi, the warning covers Wilkinson to Walthall counties and Pearl River to George counties, continuing south almost to the Gulf and north into Perry, Green and Wayne counties. Forecasters say the exception will be places on the coast.
In Louisiana, it affects St. Helena, Washington, St. Tammany, and Tangipahoa parishes.