Polar vortex? Chance of arctic air coming to Long Island next week a 'flip of the coin,' forecasters say.

A rare weather event next week expected to spur a wave of unusually cold conditions throughout the country could make for a possibly frigid Thanksgiving for the region, forecasters said.

The cold temperatures — which might not reach Long Island — would be caused by a disruption in the polar vortex above the North Pole, which is a pocket of spinning air that typically keeps cold winds from flowing south, according to the National Oceanic and Atmospheric Administration.

NOAA is predicting that "waves" of air will hit the polar vortex and weaken it, allowing the cold air to leak southward and bring "more winterlike conditions across the Northwestern, Central, and Eastern U.S., including much below normal temperatures and the potential for heavy snow."

But the vortex wouldn't be felt until "around Thanksgiving and into the following weekend," according to NOAA, and the agency wrote this week there is only a 40% to 50% chance that temperatures will drop below normal on Long Island.

"How it impacts our weather remains yet to be seen," said National Weather Service meteorologist Bill Goodman. "It might just be a flip of the coin."

NOAA is predicting that areas in the middle of the country and in the northwest will be impacted first, possibly as early as next Tuesday, before the cooler weather patterns expand to the East Coast.

Goodman explained that when a polar vortex disruption does happen, it "tends to be a little bit milder than usual in the eastern U.S.," but added that the impact is hard to predict.

"There’s a lot of ways this could evolve. I think it’s premature to get too excited about what it means for our winter weather," he said. "We probably want to wait about two to four weeks. I think as far as a truly colder weather pattern getting established in the eastern U.S., maybe as we get to the middle of December — that’s probably when we would see it."

So far, Goodman said the Thanksgiving week forecast currently calls for high temperatures in the lower 50s, which he said is normal for this time of year.

He added that there’s a chance for rain on the Wednesday before Thanksgiving, when temperatures could get up into the 60s, "but other than that, pretty standard, pretty average weather for November leading up to Thanksgiving Day."

By Sam Kmack

sam.kmack@newsday.com

Sam Kmack covers the Town of Islip for Newsday. He is a graduate of the University of Southern California and previously worked as a city watchdog reporter in the Phoenix metro area, as well as an investigative journalist at the Arizona Center for Investigative Reporting.