This article was published Wednesday. A new, updated story on the cold air outbreak in the East, published Thursday, is available here: A nation divided: Polar vortex to unload historic Arctic blast in the East, as blistering heat roasts West

Let us preface this with “yes, really.”

After remaining well-behaved all winter, the mischievous polar vortex is set to thrust a lobe of frigid, wintry air south over the eastern United States, bringing snow to places in the Northeast and Mid-Atlantic and chilly temperatures from the Upper Midwest to New England.

Frost could even visit places such as northern Georgia and the western Carolinas late this weekend as the expansive cold air mass settles south and challenges records. Temperatures in many places will feel more like early March than early May.

A dollop of wintry mischief, including the potential for a few areas of accumulating snow, is also on tap along the Appalachians from North Carolina through Maine. In some areas, a coating or more of snow is possible — especially across central and northern New England late Friday and early Saturday.

Even where the flakes don’t fly, temperatures will still sit some 20 degrees or more below average as a strong cold front slides all the way down near the Gulf Coast, with temperatures falling into the 30s and 40s in its wake. Mother’s Day could feel more like St. Patrick’s Day in some areas before a gradual recovery occurs next week.

The chilly details

The cold air mass will arrive in the eastern half of the Lower 48 in time for the weekend, stretching from the Interstate 35 corridor through the Plains all the way to the East Coast. Temperatures across an expansive region will be some 15 or more degrees below average. Cold temperatures will even make it to parts of Mississippi and Alabama.

The Upper Midwest and Great Lakes are slated to get the core of the cold first starting as soon as Friday. High temperatures in Minneapolis, on the western fringe of the cold, is expected to stay in the upper 40s on Friday. Chicago may not make it above 45 degrees, one day after enjoying sunny skies with the high in the mid-60s.

Such a cold daily maximum temperature would be the coolest May high temperature observed in the Windy City since 2005.

The cold will spill far to the south and east, bringing a chance of frost to places in northern Georgia or the higher elevations of the Carolinas. While Saturday will start quite cold, the best chance of frost or even a late-season freeze comes early Sunday morning. The National Weather Service is warning of a widespread “late frost/freeze where the growing season has already started.”

Freeze warnings are up for much of the Charleston, W.Va., area for chilly lows as early as Thursday morning, with exceptional cold — perhaps in the mid 20s — arriving to start Saturday.

Record-low maximum temperatures could be challenged in places such as Boston, Providence, R.I., and Hartford, Conn., where average highs this time of year are 64, 66 and 69 degrees, respectively. Highs in this region are unlikely to get out of the 40s on Saturday, coming within a degree or two of cold temperature records.

Washington isn’t predicted to make it above 52 on Saturday, which has happened only twice in May since 1960.

Temperatures will even be in the lower 50s for highs in New York City on Saturday; the Big Apple’s average high this time of year is close to 70.

Blame the polar vortex

The culprit for these anomalously chilly readings? The polar vortex. Ironically, as it remained mostly undisturbed between January and March, its stability resulted in a relatively mild winter in much of the contiguous United States, and cold air remained bottled up in the high latitudes.

But now a lobe of the vortex will pinch off from its main circulation closer to the Arctic, sagging southeast across the eastern Great Lakes and New England, translating to numbingly cold surface temperatures for May.

Those upper-air temperatures are likely to shatter records, and by a wide margin. Temperatures at the 500-millibar level (roughly the “halfway” point of the atmosphere’s mass, located several miles above the ground) are projected to drop to minus-30 degrees over most of Upstate New York, northern Pennsylvania, and lakes Erie and Ontario; the previous daily weather balloon-reported record over Buffalo, for Saturday at that altitude, was minus-25.2 degrees.

Of course, no one lives at the 500 millibar pressure level in this region, but meteorologists look to this temperature as an indication of how unusually cold is an air mass. With air that cold upstairs, it’s no surprise that surface temperatures are going to be chilly as well.

Snow is also on the way in the Northeast

The first symptoms of Old Man Winter’s stubborn, snowy shenanigans are likely to materialize late Friday, when a strip of low pressure will develop along the I-95 corridor between Washington and New York City. Light rain will accompany the fledgling low over the Ohio and Tennessee valleys Friday afternoon, with colder air filtering in by evening. After sunset, a few of the cold-enough spots in the interior Mid-Atlantic may change over to wet snow.

Snow will likely then come down lightly but steadily over portions of Pennsylvania by dark as well, lasting a couple of hours and accumulating up to a slushy inch before the precipitation shield shifts northeast.

In New York, areas focused along I-88 between Binghamton and Albany are the most likely areas to see steady snow.

Farther to the east, a cold, light rain will be ongoing from Washington through New York City, Hartford and Boston on Friday afternoon. A mix with or change to snow is most likely in the Berkshires; southern and central Vermont; and New Hampshire and Maine, away from the immediate coastline.

How unusual is May snowfall?

Now for the all-important question — “just how rare is this?” It’s unusual, but seeing snow in the Northeast during May is by no means unheard of.

A storm in May 1977 dropped 1.3 inches in Hartford, while Norfolk, Conn., picked up 20 inches.

The same system brought a half inch to Boston, and more than a foot to Worcester, Mass. Boston also got 0.9 inches of snow in May 1938.

Once you get up into northern Maine, however, May snow is a routine occurrence — Caribou has seen measurable snow eight times in the past 25 years.