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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 0820 UTC Sat Dec 2, 2023
Valid: 12 UTC Dec 02, 2023 - 12 UTC Dec 03, 2023
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Sat Dec 02 2023
Day 1
Valid 12Z Sat Dec 02 2023 - 12Z Sun Dec 03 2023
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR THE FLORIDA
PANHANDLE INTO LOWER SOUTHEAST ALABAMA...
...Gulf Coast and Southeast...
A strong cold front pushing east out of the Plains and into the
Southeast will draw deep Gulf moisture northeastward along and
ahead of the front. Meanwhile, a strong southwesterly jet streak
will continue intensifying from the southern Plains to the
southern Appalachians. This will put the portions of the Gulf
coast in the favorable right entrance region of the jet. Helping
intensify the jet will be a strong shortwave that will also be
tracking northeastward. While the shortwave is unlikely to have a
direct impact on the storms, it's influence on the upper jet will
help support broad scale lift over the area.
Showers and thunderstorms are ongoing across LA and MS this
morning. Heavy-rain-producing thunderstorms have been embedded
within the broader rain shield, which fortunately have been moving
enough to limit flooding impacts somewhat. Nonetheless their
tendency to produce 3 inch per hour rainfall rates at times has
resulted in localized flash flooding in portions of southwestern
LA. Storms and the broader rain shield will push off to the east
as more storms develop over the Gulf through the morning due to
the aforementioned large scale environmental lift. The heaviest
rain of the day and the greatest potential for flooding will
likely be in the morning hours/first part of the day today.
Supporting the storms are CAPE values between 500 and 1,000 J/kg
over the Gulf and the immediate Gulf Coast. Instability generally
diminishes as one goes further inland, but the increasing
southwesterly flow supported by the jet is helping advect the
unstable air mass further inland.
There's likely to be a break in the significant rainfall for much
of the afternoon through the evening hours between systems. A
renewed round of storms is expected to develop overnight tonight
into the early morning hours of Sunday. While the storms will have
more support in the upper levels as the jet streak intensifies to
over 150 kt, the time of day, faster storm motion, and lesser
forcing across the FL Panhandle and nearby portions of AL/GA
should limit both the storms' intensity and coverage tonight/early
Sunday morning.
The Slight and surrounding Marginal Risk areas are largely
unchanged with this update. Given the above reasons, the Slight
may be able to be cancelled with the midday update depending on
the evolution of the convection at that time.
...Western Oregon into far Northwest California...
The next in the long string of fronts associated with a persistent
atmospheric river is already moving into the Pacific Northwest
(primarily Washington State) this morning. The heaviest rain will
shift southward and diminish through the morning. A stronger front
will push into the far northern CA and OR coasts tonight, which is
when the bulk of the day's rainfall is expected. Expect a soaking
3 to 5 inches of rain into the coastal ranges of OR and the
Cascades through tonight, with local amounts approaching 8 inches
by Sunday morning. The impulse of moisture will be accompanied by
much warmer air typical of many atmospheric rivers. This will
rapidly raise snow levels, allowing snowmelt to contribute some to
rising river levels. Since the area has been relatively dry
recently, much of the rainfall and snowmelt should be contained in
the river banks, so only isolated flash flooding in particularly
sensitive areas is expected through Sunday morning. The Marginal
Risk was maintained with this update.
Wegman
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
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