FOUS30 KWBC 140821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Tue Jul 14 2026

Day 1 Valid 12Z Tue Jul 14 2026 - 12Z Wed Jul 15 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER SOUTH-CENTRAL TEXAS...

...Texas...

An incredibly active period on tap across the Lone Star State with
an elevated risk of flash flooding, some significant, across
portions of the state. The greatest threat will lie across the
Edwards Plateau into Hill Country and along the RGV between the Big
Bend down towards Eagle Pass. The bottom line for the setup is the environmental conditions across the southern two-thirds of the
state favor not only heavy rainfall, but very efficient rainfall as
deep layer moisture of Gulf origin will send wetbulb zero heights
to >14k ft, meaning warm cloud layers plentiful for efficient
rainfall makers. The probabilities for any cell south of I-20 to
materialize and breach 2"/hr at times is incredibly high within
both the NBM and HREF probability fields with the HREF outputs some
of the highest we've seen for widespread 2+ inch/hr rainfall
potential from a non-tropical impact standpoint. 00z RAOB from KMAF
to KDRT to KCRP all came in with PWATs running towards the 95-99th
percentile according to climatological records for the date, a
testament to the magnitude of the moisture field present and what
could transpire from any convective development.

The initial part of the period (12-20z) will be active from the
southern Concho Valley over towards coastal TX between CRP to HGX
and any point in-between as increasing low-level convergence and
the addition of multiple organized mid-level disturbances will
enhance a widespread axis of thunderstorms with the heaviest precip
initially along and east of I-35 in Central TX, spreading west-
northwestward as a weak shortwave dips south towards the Edwards
Plateau allowing for convective development to ensue by early this
afternoon. Heavy rain threat between San Antonio to Houston along
I-10 will be considerable in regards to rates and potential for
several inches of rainfall in a short time frame allowing for at
least scattered flash flood instances to occur. HREF neighborhood probs
for at least 3" of rainfall is upwards of 60-80% with a bullseye of
30-50% for greater than 5" located along that US290 corridor
between Austin and Houston, centered near Bastrop to Brenham.
Majority of CAMs are hinting at this threat in that general
vicinity, so it'll be something to keep a close eye on as we move
through the morning and early afternoon hours as the setup is
favorable for widespread 2-3+ inch totals. The I-35 corridor
between Georgetown to San Antonio is also under a threat for
significant rainfall potential, however there is some uncertainty
on this particular area for the period with some guidance
maintaining the strongest threat north and east of this region with
the other max located further west of the urban corridor. This is
still a sensitive area pertaining to the setup as any significant
convective episodes in this part of TX are notorious for rapidly
developing flash flood prospects thanks to the complex topography,
high run-off capabilities due to the sub-soil layer, and
urbanization factors. A high-end SLGT is located over this region
over into the Houston metro and all points referenced above for the
threat today, so regardless of not being in the main area of
interest further west, this is still a setup that needs to be paid
close attention.

As we step forward into the afternoon and evening hours, the focus
for the more significant flash flood threat shifts over into the
Edwards Plateau and neighboring Hill Country/RGV as convective
overspreads this area after 18z with very little breaks expected in
the convective onslaught. A multi-round punch of heavy
precipitation is likely to occur over this area of TX with
consensus on all reputable deterministic and associated ensembles
signaling a significant axis of heavy rainfall occurring in the D1
leading to likely widespread flash flood issuances, as well as some
potential for life-threatening impacts to both life and property in
the hardest hit locations. 00z HREF neighborhood probabilities for

5" stands at 60-90% for areas between Del Rio to parts of the TX

Hill Country, east of the immediate RGV. Modest probs for >8" also
exist for the same areas with 100-year ARI exceedance probabilities
settling between 30-45% over that same corridor. These types of
probabilities correlate highly to a potentially significant event
for a broader area, especially when you factor in the complex
topography, as well as multiple medium to large population centers
expected to be impacted. The period between 00-12z Wednesday will
be the time frame of interest with regards to the prolonged heavy
rain signal as a maturing LLJ and strong low to mid-level
convergence signature will initiate along either side of the Rio
Grande. A weak, but still notable 850-700mb disturbance is forecast
in proximity of the area of interest within the latest CAMs with
agreement on the development from even the ML EC-AIFS which has
been steadfast in its presentation for several consecutive runs.
Low-end QPF output is ~3" with some deterministic pushing local
maxima closer to 10" for just the D1. This is more than enough
consensus and a formidable signal to warrant a continuation of a
MDT risk across the aforementioned area with a northwestern bound
into the Big Bend and an eastern periphery located a bit west of
the I-35 corridor between Austin/San Antonio in the TX Hill Country.

The other areas that could see some locally heavy rainfall will lie
on the periphery of the broader heavy rain threat with the notable
areas between Waco to Austin and points east through east TX, as
well as southwest TX within the terrain of the Davis and Glass
Mtns, and the southern half of the Stockton Plateau. Locally
significant impacts can be seen in these areas, as well thanks to
the environmental conditions at hand. A SLGT risk encompasses both
these regions for the period with scattered flash flood warnings
plausible in either region.

Please stay tuned for the latest updates for the threat across the
state as this is an evolving situation where near term trends could
prompt upgrades at any time given observational trends throughout the D1.

...Southeast into Southern Mid Atlantic...

General consensus on widespread convective development across the
southern Carolina's into the Southeast lends to at least a broad
MRGL risk for flash flooding in any area north of I-4 with a
relative max for heavy rain situated across portions of MS/AL
thanks to the presence of a meandering upper level disturbance over
the area. WV satellite this evening pin-points a weak upper level
circulation centered over northern MS with an extremely slow
propagation to the west-southwest over the past several hours. This
particular upper circulation will be a focal point for enhanced low
to mid-level convergence later this afternoon interacting with what
is a formidable moist/unstable environment across the Southeast
CONUS. Scattered to widespread showers and thunderstorms will
materialize across northern LA over into MS and AL during peak
diurnal destabilization leading to pulse/multi-cell convective
development over the region with heavy rain prospects likely very
high considering the environment in place. Wetbulb zero heights

14k ft on forecast soundings across MS/AL indicate an effective

warm cloud layer that will likely present efficient rainfall rates
with even pulse variety convection yielding 2-3"/hr rainfall
potential during its mature phases. Slow cell motions under a weak
steering pattern situated across the Southeast will only act as an
aid to flash flood prospects over the region as cells will be more
likely to produce heavy bouts of rain for multiple hours before
drifting away from an area, or even just decaying overhead. 00z
HREF and REFS neighborhood probabilities for >3" are solidly
between 50-80% across central and south-central MS into western AL
with the main area of interest lying along and north of I-20 in
both areas. HREF blended mean outputs show a scattered 2-3" precip
signal over the aforementioned area with individual deterministic
even pushing close to 5" in the hardest hit locales. This is more
than sufficient for maintaining the previous SLGT risk forecast, as
well as wording for a high-end SLGT threshold likely over that area
encompassed within central MS to western AL.

...Southwest U.S. into the Great Basin...

Continued impacts expected from lying into the western flank of
the ridge centered over the Northern U.S. as prevailing southerly
flow will just maintain a prevalent moisture advection regime
poleward over the Desert Southwest into the Great Basin. Models
remain consistent in their interpretations of locally heavy
rainfall over both regions with the heaviest QPF centered over AZ,
but potentially greater impacts in those more flash flood prone
areas located in the interior west, including those slot canyons
over UT/NV. Rainfall rates will be the driving factor for flash
flooding in this scenario with instability generally favorable

750 J/kg MUCAPE) over a large portion of the Western CONUS. The

combination of PWAT anomalies >2 deviations above normal and
elevated instability favors at least widely scattered flash flood
potential, which this setup is leaning into the textbook signature
as forecast. 00z HREF neighborhood probabilities for >1" have a
smattering of 40-60% probs within areas of the Great Basin and
Four Corners with a more widespread 40-70% probability oriented in
the terrain from southeastern AZ up through the Mogollon Rim into
the area of the Grand Canyon. Any of these cells in the terrain
will be conducive for heavy rainfall between 0.5-1"/hr, locally
higher across the terrain with more of the general 0.25-0.75"/hr
over the Great Basin. Given the consistency in the model output and
anomalous moisture presence across the West, the previous MRGL
risk was maintained.

...Montana...

PWATs encroaching the 90-99th percentile over much of MT coupled
with favorable instability and approaching mid- level troughing to
the west will allow for scattered to perhaps widespread convection
to materialize over the Northern Rockies into Central MT later this
afternoon and evening. Ample shear and elevated moisture presence
will amplify the convective threat and proceeding heavy rainfall
posture across portions of Big Sky country as we move into the time
frame of peak diurnal destabilization. Organized cell clusters,
including a few supercells, are likely to initiate over the terrain
in the Central portion of MT with an eventual rapid storm motion
off to the northeast as the steering flow will allow for very quick propagation(s) through the High Plains of MT by later in the
evening. The best threat for heavy rainfall suitable for flash
flooding will likely occur where the initiation point occurs and
just downstream of the eventual storm motions to the northeast.
HREF probabilities for >2" are generally modest in this area with
consistency in the CAMs for cell initiation and eventual impacts in
this region northwest of Billings up through Glasgow to the
Canadian border. The previous MRGL risk was maintained given the threat.

...Northern New England...

A strong closed low analyzed over Northern Quebec this evening
will pinwheel southeast, well north of the Canadian border in New
England, but will aid in a broad brush of robust mid-level
vorticity over the northern tier of both VT/NH into western ME
during peak diurnal heating into the coming evening. MUCAPE
between 2500-3500 J/kg will be located across the northern tier of
all three states leading to a targeted area for locally heavy
rainfall with rates likely to approach close to 2"/hr as noted in
the latest HREF prob fields (10-25%) with 1"/hr rates a greater
certainty (30-50%). A quick 1-3" is forecast across this small
area of New England, however this area is notorious for local
terrain influences that could cause issues with any appreciable
rainfall in that short period of time. The previous MRGL risk was
expanded further north to include western ME given the trends in
guidance for heavy rain to impact this area as cell maturation over
neighboring Canada will likely motion into the area as we step into
the late-afternoon and early evening hours today.

Kleebauer
$$
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