THE TAKEAWAY:
- A potential nor’easter could develop later this week, bringing snow, rain and strong winds.
- One forecast scenario takes the storm inland through the Ohio Valley and eastern Great Lakes.
- Other models show the system forming closer to the East Coast.
- Colder air will begin surging into the eastern United States later this week.
A major shift in the nation’s weather pattern is expected late this week, as a potential nor’easter could affect the Northeast and New England before ushering in a sharp cold snap across much of the country.
The pattern change will begin as colder air moves into the eastern United States while warmer conditions develop across the West.
That temperature contrast will help fuel a storm system capable of producing rain, snow and gusty winds from Thursday through Saturday. Once the system moves away, temperatures will plunge across the East.
A strengthening ridge over the western United States is helping Canadian air push south into the Northeast, while warmer air builds across the West. The arrangement is providing the lift and upper-level energy needed to support an intensifying area of low pressure, setting the stage for the late-week storm.
Rather than reflecting a typical El Niño pattern, the setup is being driven by the polar jet stream. A dip in the jet stream could allow the storm to initially form somewhere between the Great Lakes and Ohio Valley before strengthening.
An unusually early disruption of the stratospheric polar vortex high above the Arctic has also helped reinforce this broader weather pattern.
Nor’easter Potential
Because the weather pattern remains so dynamic, forecast models continue to show uncertainty over the exact track and potential impacts of a developing nor’easter.
In one scenario, an initial low-pressure system would move inland across the Ohio Valley and eastern Great Lakes before gradually shifting its energy offshore. That process could lead to the formation of a secondary coastal low.
Under that setup, the immediate coast and the I-95 corridor would likely remain relatively dry. Inland and higher-elevation locations, however, could receive enough moisture for accumulating snow.
Another scenario shows the nor’easter tracking much closer to the Eastern Seaboard. In that case, the storm would develop nearer the coast, increasing the chances for heavy rain and strong wind gusts in coastal areas.
Snow could still fall inland, but accumulations would probably be limited by the lack of sufficiently cold air. The heaviest totals would most likely remain confined to higher elevations.
One wildcard in this scenario is the possibility that the storm shifts farther offshore into the open Atlantic.
A track too far east would steer much of the precipitation away from the coast, sharply reducing the threat of coastal rain and wind while also limiting snowfall inland.
That outcome is not the leading forecast at this point, but it remains possible with several days still remaining before the storm takes shape.
What We Know
Forecasters are becoming increasingly confident that a low-pressure wave will organize over the Ohio Valley late Wednesday before moving toward the Mid-Atlantic and Northeast by late Thursday.
The developing system is expected to spread widespread rain across the East, while accumulating snow will be most likely in the higher elevations of New England and the interior Northeast.
Although the supply of cold air will be limited, snow is still expected in parts of Maine, Vermont, New Hampshire and upstate New York. Snow could also extend southward into the Appalachian Mountains.
Regardless of the storm’s eventual path, any snow mixing in near the coast and along the I-95 corridor is unlikely to accumulate.
Periods of rain, relatively mild surface temperatures and insufficient cold air will make it difficult for snow to stick.
Day-by-Day Timeline
According to the FOX Forecast Center, the system will begin organizing as it moves across the Great Lakes and Ohio Valley. At first, the low-pressure system will be weak and poorly organized, producing scattered light rain with limited impacts.
By Thursday, the initial low will move toward the Northeast. With the coldest air remaining to the north, precipitation will fall mainly as rain.
Scattered showers could reach the I-95 corridor and create minor travel delays, but overall effects are expected to remain limited.
On Friday, the low will head toward the coast and try to strengthen. Because cold air will still be limited, the greatest chance for accumulating snow will be across northern New York, Vermont, New Hampshire and Maine.
This is when the two primary forecast scenarios become especially important.
If a secondary coastal low does not develop near the Mid-Atlantic, impacts along the I-95 corridor would probably remain minor, while snow totals farther inland could be lower.
If a secondary low forms farther south and offshore, however, the coastal corridor could see stronger wind gusts and perhaps a brief change from rain to snow on the storm’s back side.
By Saturday, the storm is expected to move away toward Canada. Even so, lingering moisture and colder northwesterly winds could generate snow showers from Maine south through the Appalachians, including parts of upstate New York and central Pennsylvania.
Behind the departing system, a late-autumn air mass will spread across the region, pushing afternoon temperatures into the 30s for more than 110 million people in the Northeast and surrounding areas.
A split in temperatures trailing behind
Canadian air will begin spreading across the eastern United States late Friday.
Highs could stay in the 30s and 40s across the Northeast, Great Lakes and Ohio Valley, while overnight lows fall into the 20s.
There is also a chance that the cold air could reach the Gulf Coast and Florida by Sunday.
“To give an idea of how big the swing could be, on Tuesday over 300 million Americans will be above average and only a little over 4 million Americans will be below average,” according to the FOX Forecast Center reports. “By Saturday, that number exceeds 160 million Americans below average and likely even higher into Sunday.”
As the eastern United States experiences a cold spell, warmer and drier weather will dominate the West.
Communities from California to the Great Basin and the Desert Southwest could see temperatures running 10 to 20 degrees above average.