Moderate to locally heavy precipitation associated with a Pacific low pressure system is currently overspreading northern California and into Oregon.
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The moisture will then penetrate into much of the northwestern U.S. and begin to interact with colder air slowly filtering across the northern Rockies.
This interaction will expand the coverage of snow eastward across much of the Intermountain West through the next couple of days.
The higher terrain of the Cascades, Sierra Nevada, and the northern Rockies will receive the highest snowfall amounts of as much as 2 feet with isolated heavier amounts going through Thursday.
By Friday, a reinforcing push of polar air from Canada will bring colder and drier air into the northern Plains and northern Rockies.
Meanwhile, the snow will be pushed farther south toward and into the central Rockies near and behind the polar front.
A piece of upper-level energy ejecting out of the Rockies will help develop a new low pressure system over the central High Plains and quickly head east across the central Plains Thursday night into Friday morning.
This new system will bring the next round of snow across the central Plains to the Ohio Valley on Friday with showers and some thunderstorms developing across the Mid-South by Friday afternoon.
Meanwhile, a developing wave of low pressure along a front is expected to spread a quick round of accumulating snowfall across the upper Midwest through tonight, across the Great Lakes on Thursday, and into New England Thursday night and Friday morning.
A few inches of snow can be expected to accompany this system over the upper Midwest tonight.
As the system intensifies on Thursday, 6 to 12 inches can be expected across the central Great Lakes with locally higher amounts possible.
6 to 12 inches of snow can also be expected across upstate New York into northern New England downstream from Lake Ontario due to moisture and instability enhancement as the low pressure center quickly moves across the region Thursday night and then exits New England Friday morning.
Temperatures along the Eastern Seaboard will be generally below normal into Thursday morning.
Milder air over the mid-section of the country today will spread east into much of the eastern U.S. on Thursday.
However, an reinforcing push of arctic air from Canada will bring below normal temperatures through the northern tier states on Friday with much below normal temperatures spreading into the northern High Plains.
Much of the Southwest will average near or slightly above normal through Friday. ■