Winter returns: Major pattern shift underway

By Allison Chinchar, Sara Tonks and Mary Gilbert, CNN

(CNN) — After weeks of spring-like warmth, parts of the United States will briefly plunge back into winter this week, with below-freezing temperatures possible for much of the eastern half of the country.

Tuesday marks the official start of astronomical spring in the Northern Hemisphere after the warmest winter on record.

But it seems Mother Nature has the seasons mixed up, because spring will feel more like winter early this week. More than half the US population will experience temperatures at or below freezing.

The cold isn’t just an anomaly, it will pose a risk for agricultural interests in the Southeast with the growing season underway there. Freeze warnings stretch from Texas to North Carolina because of the risk to crops.

The chilly weather will be a shock for many in the eastern half of the country experiencing warmer than average temperatures this past week. Many southern cities had highs in the 70s on Saturday – but that changed Sunday as cold crept into the Midwest and progressed south and east.

Colder air has become widespread across much of the eastern half of the country Monday and will keep most of the region quite chilly Tuesday.

St Louis could see more than a 20-degree swing from the high 60s Saturday to the low 40s Monday. Atlanta’s high temperature could drop by as much as 15 degrees from Saturday to Monday, from the low 70s to the mid-50s.

These temperatures might not be frigid, but in parts of the South they’re more typical for the heart of winter.

Memphis, Tennessee, and Huntsville, Alabama, are both forecast to see a high temperature around 50 degrees on Monday – more typical for mid-January.

The cold air will continue to spread east Monday night into Tuesday, finally reaching much of the Mid-Atlantic and Northeast. New York City will drop from a high of 61 degrees Saturday to the mid-40s Tuesday.

Philadelphia’s high temperature on Tuesday is expected to be in the upper 40s, more typical of late February.

Low temperatures will also be dropping. Temperatures in the Southeast Tuesday morning will be 10 to 15 degrees below normal for this time of the year. Atlanta, Charlotte, and Birmingham, Alabama, are all expected to see temperatures drop into the low 30s Tuesday morning, presenting the greatest risk to plants.

The timing of this potential freeze is not out of the ordinary. Birmingham, Alabama, and Atlanta experienced their final freeze right around the spring equinox last year. But the threat to plant life is more substantial given the warmth preceding it.

“Frost and freeze conditions will kill crops, other sensitive vegetation and possibly damage unprotected outdoor plumbing,” the National Weather Service in Atlanta said.

Bringing plants indoors is the easiest way to protect them from a hard freeze, but if you can’t do that, covering them can also help.

Sheets, towels or blankets can be used to help trap the radiant heat from the ground around the plants. Use stakes with your plant coverings or drape them over patio furniture so they don’t crush the plant.

Temperatures will rebound rather quickly across the Southeast by the end of the week, so hang on to that sunscreen and allergy medicine, as spring will be in full swing shortly.

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