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The latest winter system will lay down an over 2600-mile swath of snow from the Pacific Northwest, including Seattle and Portland, Oregon, to the Rockies, Plains, Midwest and Northeast into early next week.

Winter storm watches are in effect for much of the Northwest and northern Rockies, meaning there is potential for significant snow, sleet or ice accumulations that my impact travel.

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With the coldest air of the season either in place or heading in, together with an active jet stream, the stage is set for this cross-country swath of snow.

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Pacific Northwest

An impresive Arctic air mass has infiltrated not simply the Rockies, but also the entire Pacific Northwest to the coasts of Washington and Oregon.

Once this subfreezing air is in place, it can be hard to dislodge, even near the Pacific coast, particularly if it is being resupplied from the east through breaks in the Cascade Range, such as the Fraser River Valley of Washington and Columbia River Gorge.

Therefore, precipitation that falls Wednesday night into Thursday is likely to start out as snow, then may change over to freezing rain over some lower elevations of the Pacific Northwest.

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The critical uncertainty in this forecast, however, is when the subfreezing surface air near Puget Sound and the Willamette Valley gets scoured out.

For now, a couple of inches of snow seems likely to accumulate, topped by some ice accumulation (mainly in western Oregon), leading to challenging travel along parts of the Interstate-5 corridor Thursday. But, there is potential for more snow and some ice accumulations in these lower elevations if the cold air lingers longer.

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Safe to say over a foot of snow will pile up in the Cascades, Olympics, northern Rockies and Sierra, as additional disturbances in the jet stream ride over the cold air into the weekend.

Midwest/Northeast Forecast

This weekend the snowy stripe spreads into the Plains, Midwest and Northeast. Let's lay out the general timing, then discuss potential amounts.

Saturday

Snow spreads from the northern Plains into the Upper MidwestPotential cities: | | (late)

Sunday

Snow will spread through the Great Lakes into the interior Northeast.Rain or snow will fall in the Ohio Valley.Potential cities: | | | |

Monday

There is uncertainty regarding how quickly the system moves through the Northeast.Snow may linger in a stripe from parts of New England to the Ohio Valley.For now, the immediate I-95 Boston-Washington corridor looks to have rain, but we can't rule out a few wet snowflakes.Potential cities: | |

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How Much Snow?

It is too early to nail down specific snowfall forecasts for particular areas of the Midwest and Northeast.

While we're not expecting a prolific, heavy snow event, overall, some moderate to locally heavy snow totals over 6 inches are possible in a strip from the Upper Mississippi Valley to southern Great Lakes to parts of the interior Northeast.

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This is most likely where heavier, small-scale, east-to-west oriented snowbands train over a given area, like train cars over a section of railroad track. These details cannot be pinpointed this far out.

This storm may trigger weekend and Monday travel headaches both on the roads and at some major airport hubs.

Check back with us at weather.com for any changes to this forecast.

MORE ON WEATHER.COM: Seattle Snow

Gordon Jacobson (R) gives a push to Jaloni, 8, and father Tyrell Fincher at the top of a closed snow-covered street on January 18, 2012. (Stephen Brashear/Getty Images)

At a Glance

Snow will make a mess of travel Thursday in both Seattle and Portland, Oregon.A swath of the Rockies, northern Plains, Upper Midwest, Great Lakes and Northeast will also see snow into early next week.Some locally heavier totals are possible in parts of the Midwest and Northeast this weekend.