A significant winter storm associated with a strong upper-level trough and associated closed low will cross through the Ohio Valley tonight, which will continue to interact with enough cold air to produce some areas of locally heavy snowfall across portions of the Ohio Valley to the north of the low track.
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Light accumulations are expected across the Tennessee and Ohio Valleys tonight.
Farther south and east across the Southeast, and on the warm side of the strengthening area of low pressure crossing the Tennessee/Ohio Valley, the northward advance of moisture and instability from the Gulf of Mexico and its interaction with a strong frontal zone will continue to produce some heavy showers and thunderstorms across the Carolinas and Georgia early this evening before pushing into the Atlantic.
There's a Slight Risk of Excessive Rainfall leading to Flash Flooding over portions of southern South Carolina into central/southern Georgia to account for this threat.
This storm system will arrive across the Mid-Atlantic states tonight and will transition to a strong nor'easter Tuesday morning as low pressure exits off the Mid-Atlantic coast near the Delmarva and ejects well offshore of southern New England by Tuesday night.
The concern will refocus back to winter weather impacts as moisture surging northward ahead of the low center encounters sufficient levels of cold air for a swath of heavy accumulating snowfall.
There continues to be an unusual amount of uncertainty with this forecast, particularly with where the axis of snowfall will develop and occur.
The latest guidance suggests heavy snowfall occurring from southern New England down into southern Pennsylvania/New Jersey.
Generally, between 6-12 inches are probable for portions of the aforementioned areas.
The nor'easter will bring strong winds to the region on Tuesday which coupled with the heavy snowfall could damage trees and power lines.
The strong winds will also bring a threat for coastal flooding.
A new storm system meanwhile will arrive across the Northwest by the middle of the week which will bring areas of heavy rainfall to the coastal ranges of the Pacific Northwest, and heavy snowfall for the higher elevations of the Cascades.
This snowfall threat will also extend eastward into the northern Rockies as Pacific moisture streams inland. ■
Modified arctic air combined with a moisture-laden area of low pressure along the Gulf Coast will continue to allow for a broad area of winter weather impacts from the Lower Mississippi Valley to the Southeast today into early Saturday morning.