A significant change to the nation's weather takes shape late this week: a low-pressure system developing across the Ohio Valley is expected to bring rain, snow and gusty coastal winds to the Mid-Atlantic and Northeast from Thursday through Saturday, and behind it a blast of Canadian air will flip the country's temperature map — from more than 300 million Americans above average on Tuesday to more than 160 million below average by Saturday, according to the FOX Forecast Center.

Source: FOX Weather

The FOX Forecast Center says the low is expected to develop across the Ohio Valley later this week and move toward the Mid-Atlantic by Friday. 'Temperatures will turn noticeably colder beginning Friday, with the cooler pattern likely continuing through next weekend,' the center said. Afternoon highs across the Northeast, the Great Lakes and the Ohio Valley are expected to struggle in the 30s and 40s, with overnight lows dropping into the 20s.

Source: FOX Weather, quoting the FOX Forecast Center

Ten states watching for the season's first snow

The National Weather Service puts the chance at 10 percent or greater for at least 1 inch of snow beginning Thursday night across parts of the Mid-Atlantic and Northeast, and ten states are on alert for the system's wintry side: New York, Pennsylvania, West Virginia, Virginia, Vermont, New Hampshire, Maine, Massachusetts, Connecticut and Rhode Island. Forecasters are clear that the Northeast mountains have the best shot at accumulating snow — for many areas, the first snow of the season.

Source: National Weather Service outlook, reported by The Spun and FOX Weather

The Weather Prediction Center is equally clear about the limits of the forecast this far out: 'there is a chance for a low pressure system to bring mixed precipitation to the Mid-Atlantic and Northeast by next weekend. But, there remains a lot of uncertainty.' FOX Weather notes the same open questions — the exact track, snowfall amounts and coastal winds are not yet settled.

Source: Men's Journal, citing FOX Weather and the NWS Weather Prediction Center

Why the track decides everything

Two broad outcomes are on the table. If the low tracks closer to the coast, the bigger story becomes strong gusty winds and coastal impacts alongside the precipitation. If it tracks farther inland, the heaviest rain and snow shift with it. Until the track firms up over the next few days, exact snowfall numbers for any single city would be guesswork — which is why forecasters are talking in chances and ranges, not totals.

The science: a dip in the polar jet stream

The cold is being driven by a dip in the polar jet stream that lets Canadian air punch south, helped by a strong ridge building over the western United States. FOX Weather notes that an unusually early disruption of the polar vortex is occurring, but it is not a direct cause of this storm — and the system itself is not the typical El Niño pattern: it originates from the Great Lakes to the Tennessee and Ohio valleys rather than spinning up off the Southeast coast.

The other half of the map: a warm West

While the East shivers, the West bakes by November standards. From California across the Great Basin and into the desert Southwest, temperatures are expected to run 10 to 20 degrees above average — a coast-to-coast split that underlines how sharp this week's pattern change is. By Sunday, the cold could reach all the way to the Gulf Coast and Florida.

Source: FOX Weather

What it means for drivers and truckers

For the Punjabi diaspora concentrated in the Northeast — New York, New Jersey, Pennsylvania — and for truckers running I-95, I-80, I-90 and I-87, the practical risk window is Thursday night through Saturday: the season's first snow is statistically the most accident-prone, because drivers are out of practice and many vehicles are still on warm-weather tyres. Mountain stretches — the Poconos, the Catskills, the Green and White Mountains — would see any accumulation first. Freight moving between the Northeast and the Midwest crosses exactly the Ohio Valley ground where this system develops.

In short: enjoy the mild start to the week. By the weekend, most of the eastern United States will be dressing for winter — and parts of ten states may be shovelling their first snow of the season.

Source: FOX Weather