Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
737 PM EST Sat Nov 7 2026
Day 2
Valid 12Z Sun Nov 08 2026 - 12Z Mon Nov 09 2026

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTH-
CENTRAL AND SOUTH TEXAS...

...20Z Update...

The latest 12Z guidance continues to paint a wet and stormy
picture for much of south-central and southern Texas on Sunday with
the potential for scattered instances of flash flooding. Hi-res
CAMs depict rounds of persistent convection, aided by dynamic
forcing, lift, moisture, and instability all becoming maximized
across the region. 12Z RRFS neighborhood probabilities continue to
highlight high chances (>70%) for 24-hr QPF to exceed 3" across a
corridor encompassing Dimmit to Jim Wells to Zapata counties, with
RRFS EAS probabilities showing a similar but more focused signal
across Webb and Duval counties. Some higher end scenarios even show
rainfall totals of 5" or even 8" or more. Despite high flash flood
guidance and drier soils being limiting factors, the ingredients
based meteorological setup continues to point towards a potentially
impactful event. As a result, the inherited Slight Risk can now be
considered a higher end or "enhanced" Slight Risk, particularly
for the corridor of counties mentioned above. Only minor changes
were made otherwise given the broader forecast remains on track.

Miller

...Previous Discussion...

By Sunday morning, the overall synoptic evolution will lend to a
classic isentropic pattern situated over the Edwards Plateau
through Hill Country, sinking southward into South TX as we move
into the back half of Sunday. Prevailing southeast flow between the
surface to 850mb will lead to an ushering of low-level moisture
that will send PWATs surging between 1.5-2.1" with the highest
moisture prevalence located over the Southern RGV over to the Gulf
Coast, mainly south of Corpus Christi. Directional shear will
entice the potential for mesocyclone development and the ability to
sustain convection, mostly elevated, in-of a shallow surface
trough bisecting the region, leading to enhanced precipitation
rates with longevity due to the persistence in the diffluent flow
aloft. This whole setup will materialize and become a fixture for
at least 24 hrs with a broad area of moderate to heavy rainfall
with embedded convection situated across Southern TX with the core
located along and south of I-10.

Beginning to see a nice overlap in the placement of the heaviest
QPF for the period with a broad 2-3" area situated over the central
RGV over into south-central TX with a core located over the Hill
Country, down to the southeast near the area of King Ranch. Most of
the global and hi-res deterministic are quite bullish on locally
heavy totals between 4-6" with the latest 00z ECMWF even coming in
with 8+ to the east of Laredo. That seems to be the upper threshold
of the potential, especially when assessing the REFS neighborhood
probs for >5" hovering between 40-60% in the same location with a
modest 20-35% signal to the south and east. ML output is consistent
in the heavier QPF placement, as well, with the corridor of the
heaviest rain between Hill Country and the central RGV down to the
southern tip of TX near Brownsville. With general agreement among
ensembles and ML with deterministic overlap, seeing a growing
confidence in significant rainfall of >3" in places outlined. The
environmental conditions are the only thing that will keep this
from being a more prolific setup with the primary convective
posture leaning more elevated in nature as we move into Sunday
evening as noted via forecast soundings from both the RRFS and
GFS/ECMWF deterministic across South TX.

This pointed towards maintaining the previous SLGT risk forecast
with only smaller adjustments made to align with the latest >2"
probabilities within the latest REFS and NBM signaling at least at
a 30%. The core of the greatest probs continue to settle between
Laredo and Corpus Christi with emphasis on the Webb/Duval/Zapata
county areas.

Kleebauer


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt