FOUS30 KWBC 040022
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
722 PM EST Tue Dec 3 2024

Day 1
Valid 01Z Wed Dec 04 2024 - 12Z Wed Dec 04 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH TEXAS...

...01Z Update...

The Marginal Risk area for portions of South TX will be maintained
for the overnight period, with mainly the coastal areas including=20
Padre Island seeing the greatest threat still for some heavier=20
shower activity. Overall, the threat should tend to lessen
overnight with the guidance suggesting any more organized and
focused rains staying offshore. However, with surface low pressure
noted in very close proximity to Padre Island helping to focus an
axis of somewhat strong moisture convergence and an instability
gradient along the coast, there may be some locally heavy showers=20
that still develop and support some spotty 2 to 3+ inch rainfall=20
amounts overnight. Thus, any impacts are expected to be highly=20
isolated.

Orrison

Day 2
Valid 12Z Wed Dec 04 2024 - 12Z Thu Dec 05 2024

...Western Gulf Coast...

Convection is expected to move through portions of eastern TX and
LA near a weak area of baroclinic low pressure. While some
instability exists near the Upper TX Coast (500+ J/kg of CAPE), the
850 hPa inflow is veering which along with the cyclone's
progression argues for convective progression. Precipitable water
values are expected to lie mainly in the 1.5-1.75" range. Effective
bulk shear and low- level inflow appear sufficient for some level
of convective organization, but the progression should keep heavy
rainfall modest. The 12z Canadian Regional has local maxima in the
4"+ range within LA, the 12z ECMWF has backed off the amounts it
advertises across southwest LA. The 12z mesoscale guidance wasn't
emphatic on the heavy rain prospects, showing pockets of 20-30%
chance of 3"+ amounts. As flash flood guidance values are high due
to minuscule rainfall over the past week, the rainfall expected is
expected to be mostly welcome and not a significant flash flood
concern. While the threat of flash flooding is non-zero should
convection train or backbuild, which could lead to 2" an hour
totals should it happen, any occurrences would be isolated at best,
and the probability of rainfall exceeding flash flood guidance is
still considered to be less than 5 percent.

Roth

Day 3
Valid 12Z Thu Dec 05 2024 - 12Z Fri Dec 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Roth/Wegman


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!7RSVcglKshhtVVFcFMJb7fALOpDX2ItwPGw5OXx1-L6X=
sI3Mrdhn09VNrnnegsA-q0bQUfywdU1DNqtvDjFJ0qGgPIM$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!7RSVcglKshhtVVFcFMJb7fALOpDX2ItwPGw5OXx1-L6X=
sI3Mrdhn09VNrnnegsA-q0bQUfywdU1DNqtvDjFJpprqzlI$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!7RSVcglKshhtVVFcFMJb7fALOpDX2ItwPGw5OXx1-L6X=
sI3Mrdhn09VNrnnegsA-q0bQUfywdU1DNqtvDjFJNtPVzNo$=20

=3D =3D =3D
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