An unusually cold air mass has prompted the National Weather Service to issue Frost and Freeze Warnings across a large part of the country for tonight and Thursday morning. Temperatures will approach or dip below the freezing mark, possibly harming any early season plants and flowers that have been planted this spring.

In a Frost Advisory, temperatures could approach 32 to 34 degrees for a short time. While not cold enough for a solid freeze, it could be cold enough for a deadly frost. Frost could kill sensitive outdoor vegetation if left uncovered in these areas. Frost Advisories are up for portions of New Jersey, Pennsylvania, Alabama, Mississippi, Arkansas, Missouri, and Texas. The Frost Advisories are up for Wednesday morning in all areas but New Jersey and Pennsylvania; they’re in effect for Thursday morning for those two states.

In a Freeze Warning, the combination of temperatures in the low 30s or less, clearing skies, and light winds will combine to produce conditions favorable for freezing condition. In a Freeze Warning, immediate steps should be taken to protect tender plants from the cold. To prevent freezing and possible bursting of outdoor water pipes,  they should be wrapped, drained, or allowed to drip slowly. Those that have in-ground sprinkler systems should drain them and cover above-ground pipes to protect them from freezing. Freeze Warnings are up for portions of Ohio, Kentucky, Tennessee, Illinois, Missouri, Oklahoma, Arkansas, Kansas, and Texas.

All frost and freeze advisories are set to expire at 9am Thursday, local time.