FOUS30 KWBC 311600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Thu Oct 31 2024

Day 1
Valid 16Z Thu Oct 31 2024 - 12Z Fri Nov 01 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF COAST...

16Z Excessive Rainfall Discussion Update...
Only changes was a slight westward expansion of the Marginal risk
area near the Gulf of Mexico in far southeast Texas in response to
radar trends late this morning. There has been an area of enhanced
moisture flux convergence from far eastern Texas into northwestern
Louisiana during the morning which has led to some locally=20
enhanced rainfall rates with MRMS showing 3-hour totals at or above
2 inches in eastern Texas...with 3+ inches depicted in Fort Bend
and Brazoria counties. Showers and thunderstorms were already
anticipated in the Lower Mississippi Valley as mid- and upper-level
height falls and an associated surface cold front moves across the
area...with the potential for localized heavier rainfall rates
already anticipated from slow moving super cells...so the expansion
of the Marginal Risk area does not represent a significant shift in
forecast reasoning but merely accounting for short term conditions.

Bann

0830Z Excessive Rainfall Discussion...

As an upper-level trough advances through the Upper Midwest an
attendant cold front will makes its way from the Southern Plains
into the Lower and Middle Mississippi Valley. The front will slow
and/or stall most significantly into the Lower MS Valley, where
instability is expected to be maximized (while the flow and
associated forcing weakens farther north). Convection is expected
to be ongoing along and ahead of the cold front through morning,
but should increase in coverage and intensity during the afternoon
hours (while locally slowing the most from the Mid-South into
portions of the Deep South and Central Gulf Coast.With PWs nearing
2" (well above the 90th percentile, per SPC sounding climatology)
with storm motions locally as slow as 5-10 kts, the 00z HREF 40-km
neighborhood probabilities for 3"/3-hr reach as high as 20-40%.
While localized totals of only 1-2" are generally expected, the
HREF PMM QPF indicates the potential for isolated 3-4" totals (in
as little as 2-3 hours, nearing associated FFG thresholds).

Churchill/Campbell


Day 2
Valid 12Z Fri Nov 01 2024 - 12Z Sat Nov 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND ADJACENT SOUTHERN ROCKIES...

Another shortwave trough will move inland across the West on Friday
as ridging stays in place over much of the Southeastern US. Warm
Gulf moisture will be advecting northward into the southern High
Plains ahead of the trough. Meanwhile, the strongest instability
(1000+ J/kg of SB CAPE) will likely be in place over West Texas
and eastern New Mexico. Areal coverage of thunderstorms is forecast
to increase during the overnight hours (after 00z) into portions
of southeastern NM and the TX Panhandle, propagating eastward into
portions of western OK Oklahoma and far southern Kansas. Maintained
the Marginal Risk from prior cycles, given PWs increasing to 1.0"+
(above the 90th percentile, per SPC sounding climatology). While
most CAMs still do not reach out to the timeframe of interest, the
ones that do (the FV3 and CMCreg) suggest the potential for
localized 3"+ totals, as well as support from the downscaled ECMWF.
Decided to maintain the Marginal for this cycle, given considerable
uncertainty and dry antecedent soil conditions.

Churchill/Campbell


Day 3
Valid 12Z Sat Nov 02 2024 - 12Z Sun Nov 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

A much more potent longwave trough is progged to dig into the
Southwest US on Day 2, as leading shortwave impulses are expected
to result in much more organized convection over much of the
Southern Plains. Continued southerly low-level flow ahead of the
impulses should result in PWs pushing 2" (near record levels, per
SPC sounding climatology) with ample forcing (left exit region of
100+ kt subtropical jet streak) for organizing convection. The WPC
QPF calls for areal average totals of 2-3", which is still well
below the 90th percentile of the PQPF (~4-5"). Given strong
ensemble support, the inherited Slight Risk was expanded a bit
(with the expectation of verification on the higher-end of the
Slight Risk probability spectrum from Northwest TX/Big Country into
south-central OK). Given very dry antecedent conditions, a Slight
Risk was deemed sufficient (but will need to be reevaluated for
upgrade potential with future updates).

Churchill


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!498KYsnzp1R1HOg4pM5wd0Izh5EEqCKuJ1tleuhHzAib=
coHm93f5eHyaJAEGD4YPlwkBeB2WbJcSIviKokxu78zP7dI$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!498KYsnzp1R1HOg4pM5wd0Izh5EEqCKuJ1tleuhHzAib=
coHm93f5eHyaJAEGD4YPlwkBeB2WbJcSIviKokxuDEKGQP4$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!498KYsnzp1R1HOg4pM5wd0Izh5EEqCKuJ1tleuhHzAib=
coHm93f5eHyaJAEGD4YPlwkBeB2WbJcSIviKokxuav2emzQ$=20

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to
https://lists.illinois.edu and use the "Unsubscribe" link.  Otherwise email
Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.20-Linux