…Heavy coastal rain and high-elevation mountain snow over the Pacific
Northwest and northern California will become lighter and more scattered
by Thursday, followed by moderate to heavy snow along the Sierra Nevada
late Thursday to Friday…
…Locally heavy rain/flash flooding and possibly severe weather are
expected across the lower Mississippi Valley as locally heavy rain and
thunderstorms move across lower Ohio, Tennessee, and Mississippi Valleys
through tonight…
…A rapidly developing coastal storm is expected to bring a period of
gusty winds, enhanced rainfall and thunderstorms from the Carolinas to the
Mid-Atlantic states Thursday night into Friday…
Heavy lower-elevation rain and high-elevation mountain snow are currently
in progress across much of the Pacific Northwest into northern California.
Precipitation coverage and intensity will gradually decrease by tonight as
the main energy of the jet stream pushes farther inland. By Thursday,
another upper-level trough from the Pacific will begin to approach the
West Coast. Generally light to moderate elevation-dependent rain/snow will
linger across the Pacific Northwest but the precipitation will begin to
expand southward into California as the upper trough and the associated
cold front dip into the region. By late Thursday into Friday, a low
pressure system is forecast to develop over the Great Basin. This system
will bring a mix of rain and snow along with colder and windier conditions
from California into the Great Basin on Friday. Highest snowfall amounts
are expected along the Sierra Nevada where a foot of wet snow is possible.
As an expansive high pressure system continues to provide fine weather and
colder temperatures into the eastern U.S., Gulf moisture is streaming north
into the lower Mississippi Valley along a weak front together with a
remnant low pressure center associated with former Hurricane Rafael. This
system will track northeastward and merge with another low pressure system
currently moving east across the north-central U.S. The interaction of
these two systems will help trigger a broad area of showers and embedded
thunderstorms stretching from the Midwest/Great Lakes south through the
Ohio, Tennessee, and lower Mississippi Valleys through tonight. Greater
and deeper moisture content closer to the Gulf as well as some marginal
instability will bring the threat for some locally heavy downpours
producing a few inches of rain for the Lower Ohio, Tennessee, and Lower
Mississippi Valleys, where a Marginal Risk of Excessive Rainfall (level
1/4) is in effect for some isolated flash flooding. A targeted Slight Risk
(level 2/4) remains in effect from central Louisiana northeast into
central Mississippi where higher confidence in greater rainfall rates and
very wet antecedent conditions from prior heavy rainfall events may lead
to a few more scattered instances of flash flooding. The system will
continue eastward on Thursday, bringing shower and thunderstorm chances to
the upper Ohio Valley, Appalachians, and the Carolinas/Southeast, while
lingering across the Great Lakes. Some more moderate to locally heavy
rainfall totals are most likely across the central/southern Appalachians
and Carolinas where precipitation will be enhanced as a coastal storm is
forecast to develop rapidly Thursday night into Friday morning near the
North Carolina coast. This system will likely bring blustery winds and
enhanced rainfall with embedded thunderstorms on Friday for eastern North
Carolina.
Much of the central U.S. and Gulf Coast states continue to see above
average high temperatures by around 5-15 degrees this week. Forecast highs
through Thursday will range from the 40s and 50s in the Great
Lakes/Midwest; 50s in the northern Plains; 50s and 60s in the central
Plains, Middle Mississippi Valley, and Ohio Valley; the 70s for Texas and
the Lower Mississippi Valley, and the 80s along the Gulf Coast and into
Florida. Frontal passages and generally unsettled weather along the East
Coast and in the West will keep temperatures cooler and more seasonable in
these areas. Forecast highs range from the 30s and 40s in New England, the
40s and 50s in the Mid-Atlantic, and the 50s and 60s from the Carolinas
south into Georgia. In the West, highs Wednesday are in the 40s and 50s
for the Pacific Northwest and Interior West, the 60s in California, and
the 70s in the Desert Southwest. Temperatures will moderate for eastern
interior areas on Thursday as upper-level ridging builds northward, with
highs climbing into the 50s and 60s for the Rockies and Four Corners
Region, and the 80s for the Desert Southwest. By Friday, colder air will
be ushered into the West Coast while rain will keep it cool along the East
Coast.
Kong/Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
thunderstorms and isolated flash flooding concerns to the Tennessee and
Mississippi as well as the lower Ohio Valleys Wednesday
