Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
255 PM EST Sat Nov 7 2026

Day 1
Valid 16Z Sat Nov 07 2026 - 12Z Sun Nov 08 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
SOUTH, CENTRAL, AND WEST TEXAS...

...16Z Update...

GOES water vapor imagery currently shows a closed mid/upper low
digging into northwestern Mexico, with large scale forcing for
ascent increasing downstream across western Texas. Precipitation
will continue to blossom over the next several hours, though weak
elevated instability should limit rainfall rates and thus flash
flooding potential outside of localized, transient convective
cores. The relatively higher threat will begin to take shape
farther south and east across southern Texas later this evening
into tonight (and especially into Day 2/Sunday), where an
intersection of moist, easterly, upslope flow, a stout low-level
jet, and modest surface based instability lead to more sustained
convection and higher rainfall rates. Given fairly dry soils and
high FFG values, initial rainfall will likely take some time to
saturate before any localized flash flooding concerns can
materialize (which again becomes relatively more likely going into
Day 2). As a result, the current forecast remains on track and only
minor cosmetic changes were made to the current Day 1 ERO.

Miller

...Previous Discussion...

Current radar across the Southwest CONUS into west TX indicates a
steady progression of our upper trough as it migrates southeast
through AZ with the analyzed height field indicating the trough
amplifying and expected to close off over the next 12-24 hrs. As
the trough progresses into northern Mexico, anticipating the
regional ascent pattern to become favored across southwest TX
through the Big Bend leading to minor flash flood prospects within
the diffluent pattern materializing downstream of the trough/upper
low once it develops. Models remain consistent in their
presentations of scattered convective pulses, most of which will be
weak and elevated in their organization leading to relatively low
chances for flash flooding for areas west of the Pecos River today,
but threat is non-zero based on some of the low-end probs, but not
enough for a broad risk (MRGL).

Across the Stockton Plateau into the Edwards Plateau and
neighboring Rio Grande Valley (RGV), the threat will be delayed
compared to upstream as the main convective prospects in the
afternoon and early evening will be back into Mexico as the primary
ascent will be focused within the Mexican State of Coahuila and
the in the vicinity of the Serranias del Burro. By the evening into
the early morning hours Sunday, expecting a quick development of
elevated convection across the RGV into those neighboring areas
with the REFS indicating a pretty strong signature for heavy rain
across the area between Val Verde down through Maverick counties
and counties adjacent. This makes sense synoptically as we begin
seeing the influence of increasingly diffluent flow into the RGV
with an intersection of a modest 30kt LLJ funneling up the Rio
Grande, advecting a richer moisture source within the sfc-700mb
layer that can be tapped into for more efficient rainfall
prospects.

REFS neighborhood and EAS probs indicate a relatively solid chance
for locally 1-2" of rainfall along the RGV with perhaps some
protrusion into the western edge of Hill Country. This is mainly
the beginning of the more active setup that will translate into the
eventual D2, but the initial threat will offer a low-end prospect
for flash flooding, especially in any urban zones along the RGV up
into the Lower Trans Pecos where run off capabilities are higher. A
MRGL risk continues to compass those areas of the Stockton
Plateau, across into the Concho Valley, and down the Rio Grande
with emphasis on the central RGV between Del Rio to Laredo.

Kleebauer


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 3
Valid 12Z Mon Nov 09 2026 - 12Z Tue Nov 10 2026

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

...20Z Update...

Scattered convection with embedded cores of heavier rainfall will
likely be ongoing across portions of southern Texas to begin the
Day 3 period Monday morning, with a gradual weakening trend
expected through Monday afternoon and evening. Despite the forecast
for weakening, the latest models continue to highlight the
potential for an additional 1-2" of rainfall, mainly overlapped
with the Slight Risk area from Day 2/Sunday. Given the additional
expected rainfall and potential for impacts to linger into Day
3/Monday, largely maintained the inherited Marginal Risk and made
only minor changes to align with the latest QPF.

Miller

...Previous Discussion...

The pattern will begin to breakdown across the Southern Plains with
drier air filtering back in from the north and primary ascent
pattern fading with the mid and upper level evolution taking place.
Guidance continues to lean into a short time frame in the D3 where
some heavy rain chances linger into Monday morning before we
finally see the threat scale completely back and the chances end
from west to east. Additional totals of 1-2" are possible as noted
via some of the global deterministic. The most notable area of
interest will likely be over the immediate southern TX coast where
the greatest instability and the likely final spot that sees the
precip pattern move out. This allowed for confidence in continuing
the previous MRGL risk with some adjustment based on the ensemble
mean QPF distribution. Not anticipating significant impacts to the
southeast TX coastal plain, but will be an area to watch,
especially if the threat ends up being a little further west into
the population centers of far southern TX. If the heaviest rainfall
anchors to the coast, that will likely limit more appreciable
impacts due to the sandier soils and lower urban footprint.

Kleebauer


Day 4 and Day 5

Valid 12Z Tue Nov 10 2026 - 12Z Thu Nov 12 2026

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

Bann


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt