FOUS30 KWBC 130830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Mon Jul 13 2026

Day 2  Valid 12Z Tue Jul 14 2026 - 12Z Wed Jul 15 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE EDWARDS PLATEAU, CENTRAL RIO GRANDE VALLEY, AND HILL COUNTRY...

...Texas...

A significant, multi-day threat for heavy rainfall will begin on
Tuesday across portions of west TX with the threat looming largest
over the areas along and west of the Rio Grande near and south of
I-10. There has been a growing consensus over the last several days
of significant rainfall potential brewing across the Edwards
Plateau and surrounding areas with the setup a textbook case of
primed low- level convergence thanks to frontal positioning and the
threat of an approaching MCV complex migrating westward from
Central TX. Latest CAMs are finally in range of the threat, at
least the initial setup leading into what will be a very active
Tuesday night and Wednesday morning across areas west of I-35 along
and south of I-10 into Hill Country. Disturbance moving into the
region will only act as a provider for sufficient low-level
convergence in an already buoyant environment situated over much of
the southern half of TX. LLJ enhancement over the RGV will only
act as a beneficial product for low-level moisture transport and
convergence which will allow for a focused axis of heavy rainfall
to materialize and slowly drift over the same areas for several
hours once the activity initiates. ML guidance and global ensembles
have been extremely consistent in their interpretations of what
will transpire with little wavering in the axis of heaviest QPF and
only providing greater magnitudes as we move closer in time.

Mean QPF for the D2 time frame is now upwards of 3-4", locally
higher across much of the Edwards Plateau with the focus over Del
Rio and points east into Hill Country. Bias corrected ensemble is
also indicating some 4-5" totals as of the latest iteration, a
signature generally seen for events of upper echelon potential.
Considering the favorable environment and likely efficient rainfall
given PWATs between 2-2.2" forecast, prospects for >2"/hr rainfall
are not only certain, but there's a threat for even some 3-4"/hr
rates in the strongest cell cores that could push totals for the
first day of the event to >5", as noted via modest probs within the
NBM over the area. In coordination with the local SJT and EWX
offices, a MDT risk was added across the aforementioned areas with
emphasis on the Edwards Plateau where the most consistent signals
for >3" rainfall exist among all ensembles.

Across central and southwest TX, locally heavy rainfall prospects
will only continue, with the latter the most likely to see some
type of overlap in the general convective coverage as thunderstorms
focus over the regional topography from the Davis Mtns. into the
Stockton Plateau. Central TX is a toss-up currently with the
greatest threat likely to be in proximity to the quasi-stationary
front and any lingering outflows that materialize from
convection the previous period. Models are generally aggressive
in-of San Antonio and the I-10 corridor for the first half of the
forecast, so it will be interesting to see the trends as we step
forward in time. For now, a broad high-end SLGT is forecast over
the above areas, but there is potential for an upgrade in either
area, pending trends in hi-res guidance and observational trends as
convection occurs from the end of D1 into D2.

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

Continued impacts 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. The previous MRGL risk was maintained with some expansion
further north around the area of the Sierra's.

...Northern Rockies...

PWATs encroaching the 90-99th percentile over the western half 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
Tuesday afternoon and evening. Totals are currently relatively
meager in an areal average sense, however some of the deterministic
are producing some local 1-2" amounts with impacts realistically
only a few hours, at best when convection occurs. These types of
rates are historically favorable for flash flood prospects across
the Northern Rockies, so the previous MRGL risk was maintained
over the area as the signal remains consistent.

...Northern Vermont and New Hampshire...

A strong closed low over Northern Quebec 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 during peak diurnal heating. MUCAPE between 2500-3500
J/kg will be located across the northern tier of both 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. 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. A MRGL risk was added for the threat in
the above area.

Kleebauer


Day 3  Valid 12Z Wed Jul 15 2026 - 12Z Thu Jul 16 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE LOWER TRANS PECOS, EDWARDS PLATEAU, RIO GRANDE VALLEY, AND
HILL COUNTRY...

...Texas...

Setup from the D2 will linger into D3 a our mid-level disturbance
is likely to meander for at least one more period leading to low-
level convergence pattern continuing across the same areas impacted
in the D2. Models are consistent in the signature for an additional
round of heavy rainfall centered over the Edwards Plateau with a
bit more of a northern extension into the Lower Trans Pecos and
lower Concho Valley. Considering the overlap from the previous
period, multi-day totals are upwards of 6-8" currently with areas
of 10+ inches plausible when you consider the low-bias in some of
the global deterministic outputs when it comes to convection. The
setup is one that signals significant flash flood concerns given
the multi-day impact and the forecasted totals in place. A MDT risk
was introduced for the above areas to account for the impacts on
back-to-back days, as well as the agreement in ensembles and ML
outputs that can be traced back to the last 3-4 days exhibiting a
consistent result. This period will need to monitored for further
upgrades as we move forward in time as a lot will stem from what
happens the prior periods.

...Western U.S...

Broad upper ridge centered over the Northern U.S. will continue to
provide significant moisture advection into the interior west
leading to scattered convective signals from the Canadian border
down into the Desert Southwest with flash flood concerns in those
more susceptible areas out west. This setup is is a continuation
from the previous period, but the expansion of heavy rainfall is
further east comparatively as the ridge nudges eastward and shifts
the general pattern in tandem. Broad MRGL risk exists for the
period across the West.

Kleebauer
$$

--- Scorpio BBS
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