Winter makes a comeback on the East Coast

Published 7:00 am Tuesday, March 14, 2017

By Skip Rigney

And you thought winter was over. March is a month full of contradictory signals in the weather, and the change in our temperatures from last week to this week will provide a good illustration.

The same weather pattern that is bringing a winter storm to the Mid-Atlantic and Northeast will drag unseasonably cold air from Canada all the way into the Gulf of Mexico over the next couple of days.

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The weather map for altitudes several miles above the Earth’s surface has shown a big ridge of relatively warm high pressure over the western United States for the last several days. On Sunday, high above the eastern Pacific Ocean, a large patch of strong winds with speeds over 150 miles per hour was headed into Canada around the northern edge of that western ridge.

Last night and today all that energy was plunged southeastward out of Canada into the central and eastern United States. That additional energy at jet stream altitudes will have several impacts.

One effect will be to combine with another streak of strong high altitude winds moving northeast out of the Gulf of Mexico to generate a deep surface low-pressure system just off the East Coast.

Secondly, the jet stream energy diving southeastward out of Canada will push a cold dome of high pressure at the surface into

the central and eastern United States.

That cold air will combine with the deep surface low off of the East Coast to cause one of the most powerful nor’easters of the season from Maryland to Massachusetts. “Nor’easter” is a term coined in recognition of the prevailing wind direction on the East Coast during the worst winter storms there. This one will dump at least six inches of snow on millions of people, and some folks will receive over a foot.

In the South, however, we are too far removed from the low-pressure cyclone to be bothered by any of its storminess. Instead, our weather will be dominated by the dry, cold surface high pressure sliding southward out of Canada.

Clear skies will allow much of the heat gained from the sun during the daylight hours to escape the next two nights. Forecasters in the National Weather Service Forecast Office in Slidell are expecting low temperatures to fall into the 30s tonight and Wednesday night. At least some folks in the county may see frost early Thursday morning.

Even with bright spring sunshine our maximum temperatures Wednesday and Thursday will only make it to near 60 degrees.

This early spring cold snap will be colder than what we experienced on 75 percent of the days during the unusually warm winter months of December, January, and February that just ended.

By Friday, the centerline of the surface ridge of high pressure will be located to our east, which means that our winds will shift around to southerly bringing warmer more humid air in from the Gulf.

Over the weekend a weak cool front approaching from the north may give us a slight chance of showers, but for the most part Saturday and Sunday look mostly dry with temperatures back to warmer-than-average levels.

Highs this weekend are forecast to be in the 70s, lows in the 50s.