…Heavy coastal rain and high-elevation mountain snow expected to reach
the Pacific Northwest and northern California this evening…
…Showers and thunderstorms will bring locally heavy rainfall, some
strong thunderstorms and isolated flash flooding concerns to the Tennessee
and Mississippi as well as the lower Ohio Valleys on Wednesday…
…Above average temperatures continue for much of the central U.S. and
Gulf Coast states while colder air moves into the Northeast and the West…
A low pressure system developing over the central High Plains will quickly
move across the north-central U.S. tonight. Light to moderate
lower-elevation wintry mix and higher-elevation snow associated with the
low pressure system across the northern Rockies and Great Basin will move
into the central Rockies this evening and then gradually taper off
tonight. Meanwhile, another Pacific frontal system and accompanying
Atmospheric River will approach the West, bringing a wave of Pacific
moisture and triggering increasingly heavier lower elevation/coastal rain
and higher elevation mountain snow by this evening. The system will move
swiftly inland, bringing an expanding area of lower elevation/coastal rain
and high elevation mountain snow to northern California and a wintry mix
into the northern Rockies and Great Basin through Wednesday. Favorable
upslope regions along the coastal ranges and Cascades will see locally
heavy rainfall and the threat of some isolated flooding today, expanding
southward into coastal northern California on Wednesday. By Wednesday
night into Thursday, the precipitation coverage across the West will
gradually decrease with time as the main energy of the system continues to
progress east into a dry ridge of high pressure in the Rockies. The rain
will continue to linger into Thursday afternoon near the coast of the
Pacific Northwest along with some high-elevation snow over northern Idaho.
Across much of the eastern U.S., fine and colder weather is expected to
overspread the region for the next couple of days as an expansive high
pressure system takes control behind an exiting low pressure system.
Meanwhile, a cold front trailing south from the developing low pressure
system over the north-central U.S. will push eastward against the
expansive high pressure system in the East. Moisture returning from the
Gulf of Mexico will then interact with the cold front and produce a couple
of expanding areas of moderate to heavy rain with embedded
thunderstorms–one near the central Gulf Coast states, and another across
north-central U.S. ahead of the cold front. The rain and thunderstorms
over the central Gulf Coast is associated with the remnants of Hurricane
Rafael which has been meandering over the central Gulf of Mexico for the
past couple of days. These two areas of expanding rain and thunderstorms
are forecast to merge near the mid-Mississippi Valley on Wednesday to
produce widespread moderate to locally heavy rainfall across the lower
Ohio and Tennessee Valleys, Mid-South, and into the lower Mississippi
Valley. Some isolated flash flooding is possible especially given wet
antecedent conditions from recent rainfalls. More light to moderate
rainfall is likely over the Great Lakes with lower instability and
available moisture. The system will push eastward into the Appalachians
Wednesday night into Thursday morning with moderate to possibly locally
heavy rain. By Thursday afternoon, the rain will reach into the
Mid-Atlantic and into the Carolinas as a low pressure system develops
along a coastal front just off the coastline of the Carolinas.
Much of the central and eastern U.S. will continue to see above average
high temperatures of 5-15 degrees over the next couple of days. Forecast
highs range from the 40s in the Great Lakes, 50s in the northern Plains,
60s for the central Plains, 70s for Texas and the Southeast, and 80s along
the Gulf Coast. Colder air will move across the Great Lakes into the
Northeast while more seasonable temperatures will come to the Carolinas
and Southeast on Wednesday, with highs dropping into the upper 50s to
mid-60s. Rain will keep temperatures cooler up the East Coast on Thursday.
The multiple frontal systems will keep temperatures cooler across most of
the West as well, with highs Tuesday mostly in the 40s and 50s for the
Pacific Northwest and interior locations, 60s for coastal California, and
60s and 70s for the Desert Southwest. Conditions will moderate by around
5-10 degrees on Wednesday and into Thursday.
Kong/Putnam
Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
