FOUS30 KWBC 031846
QPFERD

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

Day 1
Valid 16Z Tue Dec 03 2024 - 12Z Wed Dec 04 2024

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

...16z Update...

No changes needed to the inherited Marginal Risk, as an isolated
instance or two of flash flooding remains possible over portions
of South TX. The 12z HREF continues to support the idea of
isolated 3-5" totals near the coast (though some members keep
nearly all of the deep convection just offshore).

Churchill


...Previous Discussion...
A moist airmass (characterized by 1.4+ inch PW values) will=20
migrate slowly northwestward through the day along a surface trough
located near the south Texas coast. Convergence along that trough=20
axis will support areas of deep convection through the day, with=20
kinematic profiles supporting slow storm motions even as mid-level=20
flow weakens during the forecast period. Isolated spots of 2-4 inch
rainfall amounts appear possible per latest CAMS in the Marginal=20
Risk area. Isolated flash flood potential will exist in this=20
regime.

Cook


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=20
LA near a weak area of baroclinic low pressure. While some=20
instability exists near the Upper TX Coast (500+ J/kg of CAPE), the
850 hPa inflow is veering which along with the cyclone's=20
progression argues for convective progression. Precipitable water=20
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=20
of convective organization, but the progression should keep heavy=20
rainfall modest. The 12z Canadian Regional has local maxima in the=20
4"+ range within LA, the 12z ECMWF has backed off the amounts it=20
advertises across southwest LA. The 12z mesoscale guidance wasn't=20
emphatic on the heavy rain prospects, showing pockets of 20-30%=20
chance of 3"+ amounts. As flash flood guidance values are high due=20
to minuscule rainfall over the past week, the rainfall expected is=20
expected to be mostly welcome and not a significant flash flood=20
concern. While the threat of flash flooding is non-zero should=20
convection train or backbuild, which could lead to 2" an hour=20
totals should it happen, any occurrences would be isolated at best,
and the probability of rainfall exceeding flash flood guidance is=20
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!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh=
mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG1NTLjQp0$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh=
mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG1PueUiZk$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!-JNPMi0I351-aVI304flnfpOPNh6KFSxGVuZec4s7BCh=
mi8SgdjFAbpE3LcLYJUc7l5L8oK1kkDVkj78nZG13aWxpnE$=20

=3D =3D =3D
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