Record-Early Polar Vortex Break Puts a Chill in the Thanksgiving Outlook as the West Braces for More Sierra Snow

After a frosty weekend for much of the eastern half of the country, next week's weather looks calmer for many Americans, with milder air returning to the East, a soaking Sunday for the Texas Gulf Coast and round after round of mountain snow in the West. But forecasters are keeping one eye on something far above our heads: a record-early breakdown of the polar vortex that could tilt the pattern colder by the time families hit the road for Thanksgiving on Nov. 26.

In the East, this week's chill was real but not extreme. CNN reported that nearly everywhere east of the Mississippi River was in line for its coldest weather since spring, while noting the cold was not expected to be particularly severe. The relief should not take long: CNN said above-average temperatures are set to return to the eastern United States and other regions next week.

Along the Texas coast, Sunday is the day to watch. The Houston Chronicle reported that the federal Weather Prediction Center expects 2 to 4 inches of rain in areas near and north of Houston through Monday morning, enough to bring a risk of street flooding. Drivers there should give themselves extra time Sunday and never try to cross a flooded road.

Out West, the storm parade is just getting started. The San Francisco Chronicle reported that blizzard conditions were expected above 7,000 feet in the Sierra Nevada on Friday afternoon and evening, and that long-range computer models show at least two more chances for snow across the Sierra next week. Travelers headed for Lake Tahoe should carry chains and check road conditions first.

The bigger story for the rest of November is happening miles above the Arctic. The polar vortex is a band of strong winds that normally spins around the North Pole and keeps the coldest air bottled up there. When the stratosphere over the Arctic warms suddenly, that circulation can weaken or break apart, and frigid air can slosh south.

That is what is happening now, and unusually early. CNN reported that the vortex broke down earlier than ever recorded, with a major sudden stratospheric warming event underway as of Thursday. The Fox Forecast Center likewise found that the vortex has been disrupted at the earliest point in a calendar year on record.

What that means on the ground is still an open question. The Washington Post reported that the disruption could send Arctic air spilling into the United States from late November into December, but that its effects could be muted by a record El Niño, which has already helped give much of the country an exceptionally mild start to November. The Post said the Climate Prediction Center described a disruption like this as "very rare" for November, and that the agency's long-range outlook still favors above-average temperatures across much of the northern United States through December.

Weather.com reported that the weak vortex could bring a chillier pattern to parts of the country as soon as Thanksgiving week, possibly lasting into early December. It added a caution: the air waiting in Canada and the Arctic right now is not especially cold, which works against a severe outbreak. Fox Weather was more reserved still, reporting that computer models are not showing any major cold-air outbreaks in the near future and that any noticeable effects are more likely in late November or December. Fox Weather also noted that a strong El Niño and an active Pacific jet stream tend to favor warmer-than-average conditions across much of the northern tier.

CNN reported that a NOAA researcher expects the vortex to strengthen again fairly quickly after this event, though another disruption later this winter would not come as a surprise.

The honest answer is that no forecaster can yet promise a cold or snowy Thanksgiving, and specific storms cannot be pinned down two weeks out. What the experts are telling us is that a colder turn is possible late in the month, even as El Niño pushes the other way.

For travelers, that means a few simple steps now. Watch the forecast as the holiday approaches, keep flexible travel times if you can, put a blanket, water and a phone charger in the car, and check on elderly neighbors and relatives when the first real cold arrives. Those living in the West should expect mountain passes to stay snowy and slick through next week, and Gulf Coast residents should keep Sunday's flood risk in mind before heading out.

There is something humbling about a season that can still surprise the best scientists and their computer models. Scripture reminds us that the Lord "giveth snow like wool" and scatters the frost like ashes. As the cold air gathers somewhere over the top of the world, it is a good week to prepare wisely, give thanks for the warm homes and full tables so many of us enjoy, and remember those who will spend this season without either. We will keep watching the forecast and bring you the latest as Thanksgiving week draws near.