A relatively warm and wet weather pattern overspreading the Nation through
at least the next few days is anticipated to produce heavy precipitation
across the West Coast and parts of the Deep South. For the western U.S., a
lull in unsettled weather today will be replaced by potentially excessive
rainfall and heavy mountain snow beginning on Thursday as an initial wave
of moisture moves onshore followed by a potent atmospheric river. Most of
the potential impacts are anticipated across central/northern California
and parts of southwest Oregon. Here, rainfall amounts of 3 to 6 inches are
forecast through early this weekend. Heavy rain may lead to scattered
instances of flash flooding, especially near recent burn scars where
terrain is most susceptible to rapid runoff. A Slight Risk (level 2/4) of
Excessive Rainfall has been issued for these regions in order to further
highlight the flash flood threat. Heavy snow is possible across the higher
elevations of the Cascades and Sierra, with storm total snowfall amounts
up to several feet are possible. Most of the snow will be confined to the
highest terrain as warm Pacific air pushes snow levels very high and
generally above pass level. Moisture will also spread into the
Intermountain West along the strong Pacific jet stream, with moderate to
heavy snow possible across northern Nevada by Friday night.
Shifting to the central and eastern U.S., an upper-level trough swinging
into the Great Plains tonight in conjunction with a high pressure system
sliding off the East Coast will allow for an abundance of warm and moist
air to surge northward out of the Gulf of Mexico. A quick-hitting swath of
snowfall is possible to the north of a developing low pressure system
between tonight and Thursday as it progresses from Kansas to the Upper
Midwest. The best chances for over 4 inches of snow is currently expected
to remain confined to central High Plains of Colorado. Farther east,
shower and thunderstorm activity is anticipated to develop across parts of
eastern Texas and the Lower Mississippi Valley on Thursday and Friday as
atmospheric moisture content increases ahead of an approaching cold front.
Some isolated storms could turn severe, with damaging wind gusts the
primary risk. A few instances of flash flooding are also possible. The
active weather is expected to shift east by the end of the week and
produce locally heavy rainfall from the central Gulf Coast to parts of the
Ohio Valley.