Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
312 AM EST Sun Nov 8 2026

Day 1
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...

Current UA analysis and WV satellite presentation depict a deep,
closed upper reflection positioned over northern MX with a
prevailing southwest flow aloft encompassing the Southern Plains
of TX. A modest diffluent signature within the associated height
fields indicate a persistent ascent pattern between the Big Bend
down into the lower Rio Grande Valley (RGV) leading to copious
waves of showers and thunderstorms positioned along the RGV,
extending northeast into the northeastern part of the state. Recent
radar trends indicate a larger areal extent of convection
positioned along the immediate RGV as the coupling of large scale
ascent from our trough/ULL over MX interacts with a budding 30-40kt
LLJ centered basically on top of the RGV itself. This setup is
going according to plan with guidance and the current analysis in-
line with the general synoptic evolution and the precipitation
distribution across the state. Expectation is for heavy rainfall to
continue with a conglomeration of convection centered over south-
central TX in the vicinity of a strengthening surface trough
positioned over the interior portions of South Texas, mainly
bisecting the areas between Bexar county down to Cameron at the
southern tip of the state.

Assessment of the hi-res CAMs indicate a multi-wave scenario with
one round of heavy rainfall in the early portion of the forecast
transitioning to a complex of convection centered over the eastern
sections of Webb county over towards Corpus Christi by the
afternoon. Latest hi-res ensemble outputs note a solid 2-4",
locally higher occurring during the afternoon and early evening
hours before we see some re- firing of the convection over Deep
South TX with the re- development of the nocturnal LLJ tonight into
early Monday. REFS blended mean QPF is fairly robust with a
widespread 3-6" with as much as 8" occurring during the full
period with rates generally capped between 1-2"/hr at peak
intensity as MUCAPE will remain relatively low despite the modest
theta_E presence. REFS neighborhood probabilities for >3" remain
elevated with a large area of 60-90% probs centered over much of
South TX, mainly south of I-10 with the highest threat over the
area encompassed by Webb county over towards Corpus Christi. This
area, despite fairly high FFG thresholds, will still have a better
than normal opportunity for flash flooding due to extended priming
and longevity of the convective pattern overhead. Rainfall rates
coupled with the longstanding expectation of moderate to heavy rain
will boost the threat as we move forward in the D1 leading to the
best chances occurring in the late-afternoon and evening time frame
today, carrying into early Monday morning.

The previous SLGT and enhanced SLGT forecast was relatively
unchanged from the last update as guidance remains in solid
agreement on the convective details and heavy precipitation
positioning. A targeted upgrade is possible pending the evolution
and observed trends in the rainfall accumulations and relevant
flood obs that could occur. This would likely be proposed in future
updates, but current indications signal a continuation of the SLGT
risk with enhanced wording for those above locations.

Kleebauer
 

Day 2
Valid 12Z Mon Nov 09 2026 - 12Z Tue Nov 10 2026

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

Expectation is for the setup to begin slowly breaking down on
Monday with the mid and upper level pattern transitioning from less
of a closed reflection to a more positively tilted upper trough
positioned over the Southern Plains. The low-level flow will remain
more east to northeast across all of South Texas leading to a small
area of convergence within proximity to a decaying surface trough
positioned over the region. Models are consistent in their
interpretation of lingering rainfall for areas south and southeast
of I-10 with the best threat likely over the interior areas to the
west and northwest of Corpus Christi, down through the far South
Texas coastal plain. Models are typically within the range of an
additional 0.5-1" on average with locally higher totals possible in
a narrow corridor along the decaying surface trough. That said,
there's a few ensemble members from the REFS suite, as well as the
HRRR that are more bullish with local totals pushing 2-4"
additional, on top of what will already be a very saturated ground
after what transpires on D1. It's something we'll monitor closely
as this would prompt a short term upgrade until the threat fully
wanes after 18z Monday, an agreement from all models with a sharp
decline in FFG exceedance probabilities for all 1/3/6 hour
thresholds. The previous MRGL risk was maintained as a result, but
will assess in the coming forecast updates to see if a targeted
upgrade is necessary for that area just inland of the South TX
coast.

Kleebauer
 

Day 3
Valid 12Z Tue Nov 10 2026 - 12Z Wed Nov 11 2026

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

Kleebauer
 

Day 4 and Day 5

Valid 12Z Wed Nov 11 2026 - 12Z Fri Nov 13 2026

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

Hurley
 

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