Stubborn mean upper-level troughing that has been in place over the central and eastern U.S. and led to days of heavy rain in the South will finally start to shift eastward through this weekend.
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A shortwave rounding the base of the trough has helped to induce surface cyclogenesis along a quasi-stationary boundary draped through the Southeast, with the organizing system forecast to strengthen and lift northeast spreading showers and storms up the East Coast.
Gulf moisture flowing northward with upslope enhancement along the southern Appalachians has led to a corridor of locally heavier rainfall rates/totals that could result in some scattered instances of flash flooding.
A Slight Risk of Excessive Rainfall remains in place in this region through Sunday morning.
Additional showers and thunderstorms should spread northeastward through the overnight hours and into the day Sunday through the Mid-Atlantic, though rainfall totals with northward progression should generally be lighter with only an isolated chance of any flooding concerns.
Further north, continued southeasterly moist advection from the Atlantic aided by cyclogenesis along the coast will produce a band a precipitation where colder air resides north of a lifting warm front across the Interior Northeast/New England.
A wintry mix will begin by early Sunday morning with expanding/intensifying snow showers through the day, and particularly Sunday night.
There is a moderate (40-60%) chance of snow totals exceeding 4" from the southern Tier of New York east through the Catskills and into portions of southern New England, with locally higher amounts up to 8" possible.
The snow should begin to taper off from west to east through the day Monday.
Additional moisture wrapping northwest around the system will also lead to a broad area of rain showers through the Ohio Valley and the Lower Great Lakes Saturday evening through Sunday, with the potential some snow/sleet may mix in through the Lower Great Lakes, though little to no accumulations are expected.
A series of Pacific storm systems will continue to keep unsettled weather in place across portions of the Pacific Northwest this weekend into early next week.
Moderate to locally heavy coastal/lower elevation valley rain and higher elevation snow will continue for the Pacific Northwest/interior portions of the northern Great Basin and Rockies through Sunday.
Precipitation chances will come down late Sunday and into the day Monday as one system weakens and an upper-level shortwave departs.
Another system will approach the coast later Monday, bringing renewed shower chances to coastal areas.
Temperatures broadly across the country will remain above average over the next couple of days, with the exception of some cooler than average temperatures across portions of the Southeast/Florida where conditions will be slower to moderate following a cold front passage.
Forecast highs range from the 30s in New England and Great Lakes; 40s and 50s for the Mid-Atlantic, Tennessee/Ohio Valleys, and into the Northern/Central Plains and Intermountain West; 60s for Florida and the Gulf Coast, the Southern Plains, and the West Coast; and 70s for the Desert Southwest and southern California.
Many highs along the West Coast will approach record levels for the day Sunday and Monday. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.