FOUS30 KWBC 151556
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jul 15 2026

Day 1
Valid 16Z Wed Jul 15 2026 - 12Z Thu Jul 16 2026

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

...Texas...

...The High Risk in the TX Hill Country on north to the Edwards
Plateau remains in place today...

GOES satellite and Doppler Radar show two different circulation
centers; one over the TX Hill Country producing the potent
thunderstorms in south-central TX, and an upper-level circulation
center between the Davis Mountains and Edwards Plateau. In the
short term (through early afternoon), the MCV in the Hill Country
will be the more prominent feature, spawning additional
thunderstorms for at least a few more hours. The MCV will still
have an abundance of moisture to tap into (PWs over 2") and
instability (MUCAPE >1,000 J/kg) that storms will continue to
generate 2-3"/hr rainfall rates with maximum rates around 4"/hr
possible. A brief lull in the action may ensue for some areas later
this afternoon, but as the low-level jet re- strengthens tonight,
a similar evolution to recent days will unfold where thunderstorms
form on the eastern flank of the MCV west of San Antonio on north
and west to the Edwards Plateau. New 12Z HREF does show moderate
chances (40-60%) for 6-hr QPF > 10-year ARI exceedance between
06-12Z Thurs just north of Del Rio. As seen this morning,
thunderstorms on the southern and eastern flank of the MCV has been
an ideal spot for convergence, which would still place portions of
the Hill Country seeing torrential rainfall in the path of more
flash flood concerns Thursday AM.

With rainfall amounts between 10-16" having already fallen in parts
of the Hill Country west of San Antonio, it will take very little
in the way of rainfall to prolong and exacerbate ongoing areas of
flash flooding. The latest forecast calls for another 4-8" of
rainfall with locally higher totals possible through early Thursday
morning in the Hill Country and towards the Edwards Plateau.
Significant to even catastrophic flash flooding remains likely in
the hardest hit areas through the remainder of today and into the
pre-dawn hours on Thursday. Residents are urged to monitor the
situation very closely and heed all warnings and guidance provided
by local officials, especially for those living in flood planes.

...Eastern OK & Arkansas...

In coordination with the Tulsa and Little Rock WFOs, a Slight Risk
upgrade was issued this forecast update. A sprawling 500mb trough
pivoting over the region is utilizing an abundance of moisture (PWs
between 2-2.25") and sufficient instability (500-1,000 J/kg
MLCAPE) to produce thunderstorms that are efficient rainfall
producers and are slowly pivoting along the flanks of the 500mb
trough. Latest 12Z HREF probabilistic guidance shows moderate-to-
high chances (50-70%) for rainfall totals >3" over much of central
and northwest AR, as well as into far eastern OK counties. FFGs are
not appreciably low, but the atmosphere is primed for
thunderstorms to generate up to 3"/hr rates, and in areas such as
the Ozarks with complex/rugged terrain, this setup would support
the potential for scattered flash flooding.

...Coastal South Carolina...

A Marginal Risk was issued this update given the region continues
to see a pooling of 2.0-2.3" PWs and a narrow axis of 2,000-2,500
J/kg of MLCAPE per 15Z RAP mesoanalysis. A surface frontal boundary
remains positioned around Savannah, GA and is likely to help act as
a trigger for more slow moving storms this afternoon. Storms should
be pulse like in nature, so shorter durations will help limit areal
coverage of the flash flood potential. However, given the ample
moisture and instability in place, hourly rainfall rates exceeding
3"/hr are quite possible within the more intense cells. Flash
flooding is possible again this afternoon with areas sporting more
saturated soils, low-lying and poor drainage areas, and more
urbanized communities most vulnerable.

Mullinax

---Previous Discussion---

...Central Arizona into the Interior West...

So far models remain consistent on the broad upper ridge centered
over the Northern U.S. continuing 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.
The signal for heaviest rainfall continues to be situated within
the proximity of the terrain across Central AZ where CAMs depict a
broad convective initiation after 19z centered within a defined
theta_E ridge positioned from southeastern AZ up through the
Mogollon Rim. 00z HREF neighborhood probabilities are generally
robust for at least 1" of rainfall across the terrain between
Phoenix to Flagstaff with probabilities between 60-80% showing up
over the higher terrain located within the Mogollon Rim.
Neighborhood 2" probs are relatively modest between 30-50% for the
same area, a signal sufficient enough to maintain the previously
inherited SLGT risk with only some minor adjustments on the
southeast flank of the risk. Prevailing upper level flow is still
likely to lead to precip moving southwest off the terrain and
towards the adjacent valley in south-central AZ, so the prospects
for flash flooding near Phoenix are higher than in recent periods,
but still generally favored for a MRGL risk.

Outside AZ, scattered thunderstorms are likely to materialize
within the Great Basin up into the ranges of northwest WY into
southern MT due to a continued elevated deep layer moisture
advection regime bisecting the area for another few periods. The
main concern will be flash flood threats in any urban settings and
those more susceptible slot canyons across UT and northern AZ north
of I-40. A broad MRGL risk extends north through the above areas
with isolated to widely scattered flash flood prospects expected
for these domains.

Kleebauer


Day 2
Valid 12Z Thu Jul 16 2026 - 12Z Fri Jul 17 2026

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

...Texas...

Convection will continue across the Edwards Plateau and surrounds
for at least one more period as the regional pattern maintains a
persistence in its evolution with yet another round of convection
lingering through the morning from the previous period, and one
last round of nocturnal convection anticipated the evening of
Thursday into early Friday morning. The past few iterations of the
CAMs and global deterministic are coming into better alignment on
how they have the event across TX playing out with a strengthening
signal for heavy rainfall in-of the Central RGV up through the
Concho Valley and slipping into the southeastern Permian Basin.
Ensemble means have exhibited a crescendo in the depicted areal
average QPF leading to generally robust totals bordering between
2-4", locally higher in the hardest hit locations. Considering the
nature of anticipated compromised soils and ongoing flooding across
portions of the RGV and Edwards Plateau, very little additional
rainfall would cause a myriad of problems, including an
exacerbation of any remnant flood waters, especially if impacted by
additional heavy rainfall >1"/hr as noted via the very low FFG's
already in place across the region.

The previous MDT risk was maintained and even expanded a bit
eastward through more of the Hill Country over into the Edwards
Plateau with emphasis on Val Verde county extending up to the
neighboring counties to the north, including the I-10 stretch in
central Crockett county. This is the area of greatest concern for
the setup in D2 leading to a high-end MDT risk forecast centered
over this corridor. Rainfall totals in a narrow tongue could breach
6" locally as asserted by a few of the deterministic outputs which
makes sense considering the incredibly moist environment in place.
This period will be monitored very closely and its susceptible to
larger scale changes as the setup evolves as the handling of the
MCV and the placement of the quasi- stationary front and any
surface trough axis' in the area will be foci for heavy convection.
Heavy rain will enhance life- threatening flash flooding to
portions of the region for yet another period before the setup
finally looks to break heading into D3.

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

Another round of afternoon and evening convection will transpire
across the Southwest CONUS into the Great Basin on Thursday with
the threat carrying into the early morning periods of Friday in
some locations. Models are keen on a more robust moisture advection
pulse and general instability axis across the Desert Southwest on
Thursday with a broad axis of heavy rain prospects from the
southern border all the way north into southern UT. Hi-res ensemble
and several global deterministic outputs remain very bullish on
the threat in and around the slot canyons of southern UT, along the
Mogollon Rim, and down towards the terrain embedded within
Cochise, Santa Cruz, and Pima counties. Areal average of 1-2" is
forecast for the region along the southern border with 1-1.5"
forecast across the Mogollon Rim and southern UT. Considering the
environment maturing closer to 1000-2000 J/kg MUCAPE over much of
AZ into southern UT/NV, instability and anomalous moisture within
the 90-99th percentile of climatology across the region will
produce more widespread heavy rain prospects leading to scattered
flash flood occurrences in those more susceptible locations in the
terrain. There is even some opportunity for thunderstorm genesis
off several outflows that could impact some of the larger urban
corridors within AZ, including the Phoenix metro as the environment
favors this type of potential. A broad SLGT risk was maintained
for much of AZ into southern UT with the eastern extent out towards
the NM/AZ border into the immediate Four Corners, outlining the
mean QPF closer to 0.5" from recent forecast.

...Mid-Mississippi Valley...

Remnant mid-level disturbance will slowly pivot across AR into MO
by Thursday maintaining a consistent posture of targeted mid-level
ascent and favoring greater convective coverage under the weak
circulation. The pattern is less favorable for more widespread
heavy rain prospects, especially those that would warrant more
considerable attention and a higher risk like in previous days.
Nonetheless, the signal is still there for isolated flash flood
potential within portions of the Ozarks up through the mid-
Mississippi region near St. Louis. HREF mean QPF shows a general
max near the IL/MO border near and north of St. Louis. Expecting
this signal to settle somewhere near this area given the favorable
2+ inch PWATs centered over the area. The previous MRGL was
expanded north to match the trends in guidance.

Kleebauer


Day 3
Valid 12Z Fri Jul 17 2026 - 12Z Sat Jul 18 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF WEST
TEXAS, SOUTHERN NEW MEXICO, ARIZONA, AND THE SOUTHERN GREAT BASIN...

...Texas into New Mexico...

We'll finally see a decay in the heavy rain setup across RGV and
Edwards Plateau as the upper pattern evolves to where the mid-level
trough over west TX finally caves and begins to dissolve through
daytime Friday. Despite that forecast, lingering elevated moisture
under the lower heights will allow for at least a scattered threat
of heavy convection further northwest into the Permian Basin and
Pecos River Valley out in west TX and southeastern NM. Precip
totals are considerably lower for the general forecast in the
region, however some areas that will have been hit prior will be
subject to more rainfall, so the prospects for flash flooding
remain elevated for many. Scattered thunderstorms will also
continue into the terrain over southwest TX with the greatest focus
over the Davis Mtns. Local totals over 2" are projected within the
latest ensemble bias corrected output, enough to warrant a
continued SLGT risk across the region.

Further west into the area of El Paso and southern NM, elevated
moisture and lowering heights under the westward progression of the
trough to the east will allow for a period of scattered convective
activity that could prompt heavy rain for areas that are more
susceptible to heavy rain threats. Areas like the Sacramento Mtns.
over into the Bootheel are likely to see thunderstorm genesis by
Friday afternoon, lingering into the evening before diminishing
with the loss of diurnal heating. Already have areas in the
Sacramento's still dealing with remnant burn scars from past wild
fires, so those area have the greatest threat in this setup to see
flash flooding. In coordination with the local El Paso WFO, have
expanded the SLGT to include the rest of far west TX into southern
NM.

...Western U.S...

Despite a weakening presence of the ridge that's been dictating the
overall weather pattern for the Western U.S., another active day
of widespread convection and locally heavy rainfall will plague the
region from southern AZ up through the Great Basin with a northern
extension even into parts of western MT. PWAT anomalies out west
will remain between the 90-99th percentile according to the latest
NAEFS and ECENS climatology with PWATs even encroaching on 2" down
by the Mexican border in Pima county. Textbook pattern for
monsoonal convection and likely a scattered signal for flash flood
potential with the terrain and slot canyons across the interior
west being the main focus. Heaviest QPF signature remains over
southern UT, the Mogollon Rim and southern AZ with the threat. This
is a general repeat from the previous period with the SLGT risk
coverage relatively similar as the forecasted convective pattern
maintains a similar outlook.

...Ohio Valley through the Great Lakes...

Broad theta_E ridge centered over the Ohio and Tennessee Valley's
will act as focus for diurnally driven convection during the
afternoon Friday, lingering into the evening before finally
dissipating with the loss of daytime heating. Further north into
the Northern Great Lakes, our next trough will be sweeping across
Manitoba into western Ontario with the nose of a prominent jet max
associated with the disturbance nudging into the MN Arrowhead and
neighboring U.P. Friday night. Expectation is for a blossoming of
nocturnally driven thunderstorms to materialize within Arrowhead
and neighboring Canada and press southeast as the disturbance
migrates southeastward, north of the Great Lakes. Flow will remain
generally pretty fast, so the residence time of any convection will
be short-lived. However, PWAT anomalies will be pushing upwards of
+2 standard deviations according to both the NAEFS and ECENS
outputs meaning heavy rain potential is likely with rates between
1-2"/hr likely in the stronger cell cores. MRGL risk remains over
both the Great Lakes and Ohio River Valley given the two threats.

Kleebauer


Day 4 and Day 5

Valid 12Z Sat Jul 18 2026 - 12Z Mon Jul 20 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE WEST ON SATURDAY AND SUNDAY, AND OVER THE OHIO VALLEY INTO
SOUTHERN NEW ENGLAND ON SATURDAY...

...Western U.S...
A broad active monsoonal pattern will continue across much of the
western U.S. Saturday into Sunday. An anomalous PW axis stretching
from AZ northward into MT is forecast to remain above the
climatological 90th percentile, and locally higher in some spots.
This airmass will sustain a localized flash flood threat across an
expansive corridor spanning from portions of west TX, AZ, and NM
northward to MT. On Sunday troughing over ID/MT should suppress the
ridge enough to lower PWs there, and shift the moisture axis
southeastward into more of WY and central/western CO.

We are carrying Slight risk areas on day 2 and 3 over portions of
this region, and some chance embedded Slight risks will eventually
be needed on day 4 and/or 5 as well. There should be plenty of
moisture and CAPE across the risk area to support heavy rainfall
rates and a localized flash flood risk. However, the mesoscale
details which may end up determining the eventual flash flood
coverage can not really be pinned down at this lead time, and
ensemble QPF is a bit lower compared to day 2 and 3. Thus will
hold at Marginal and continue to monitor.

...Ohio Valley into Southern New England...
On Saturday the core of the high PW airmass shifts eastward, with
2"+ PWs forecast from portions of the Mid-Atlantic into Southern
New England. Troughing building into the Northeast, accompanied by
embedded shortwave energy and favorable right entrance jet
dynamics, should support a organized convective threat from OH into
the northern Mid-Atlantic and possibly portions of the Northeast.
The Marginal risk was expanded northward into more of NY and
Southern New England with this update. Spatial uncertainties exist
regarding how far north the surface front and axis of better
instability will get, which will ultimately dictate the northern
bound of any flash flood risk. Overall this should be a progressive
system, although the eventual evolution could support a couple
rounds of convection. Given the high PWs combined with strong
850mb moisture transport and synoptic forcing...at least a
localized rainfall rate driven flash flood threat exists. We may
eventually need a targeted Slight risk as the event nears and
confidence on convective evolution and rainfall axis increases.

Further south and west across the OH Valley into the southern Mid-
Atlantic large scale forcing may be weaker, but plentiful moisture
and instability may still drive localized areas of heavy rainfall.

...Florida...
Watching the potential for heavy rainfall across the west coast
coast of FL this weekend with multiple models showing a mid-level
weakness developing over the eastern Gulf in between two strong
ridges. This setup would support a heavy rainfall threat, and
possible low pressure development. However, run to run model
consistency has not been great, and any flash flood threat over FL
will depend on if and exactly where this low to mid level
circulation sets up (heavier rain could stay primarily offshore).
Thus we will hold off on introducing any Marginal risk area at this
time and continue to monitor trends.

Chenard


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



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