453 
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
 

Day 2
Valid 12Z Wed Jul 15 2026 - 12Z Thu Jul 16 2026

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

...Texas...

Convective cluster across the Edwards Plateau and neighboring RGV
and Hill Country will likely lead to the development of an MCV
and/or a more consolidated mid-level disturbance in the region that
will remain relatively stagnant in terms of its general motion
leading to a repeat of the same pattern that will plague the area
during the D1 period. This repeating evolution of convection is a
worst- case scenario where another round of heavy rainfall will
transpire and overlap areas that will be impacted significantly the
period prior. Multi- model consensus is basically on top of each
other in the placement of the next wave of heavy rains in the
region with additional totals of 3+ inches increasingly likely
during the D2 time frame. NBM mean QPF totals for the 48hr period
are >5" around the area of Del Rio and neighboring portions of the
Edwards Plateau. Moving towards the 75th and 90th percentile
forecasts, NBM jumps significantly into 6" and 8", respectively for
each data point. Widespread 3-6" totals are likely in the 2-day
period, but it is within the realm of possibility that additional
rainfall on D2 will push totals in areas above 10 inches, a
threshold that likely spell major flash flooding and hydrologic
impacts that will encroach more severe levels compared to the
normal scenarios from the past.

The setup continues to show great consistency within the latest
ensemble and deterministic outputs which does add value to the
forecast as this provides greater confidence in a high level event
brewing as we step through the D2 period. The previous MDT risk was
generally maintained with just some minor adjustments on the
eastern and southern flank of the risk. This period, and the event
in question will need to be monitored for a potential upgrade to a
High Risk which will likely occur once we see how the initial
evolution is transpiring. No matter the case, life-threatening
flash flooding and significant hydrologic concerns are increasingly
likely for the D2 period with the heaviest rainfall likely to occur
in the initial start of the D2 and after 00z Thursday when the
nocturnal LLJ initiates and provides a fresh low-level moisture
injection and enhanced convergence within the proximity of any
lingering disturbance. A high-end MDT risk remains in effect for
those areas referenced above with a broader MDT extension out into
Hill Country and over into the Lower Trans Pecos to Big Bend.

...Mogollon Rim into Central Arizona...

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. Increased confidence in a locally
favorable convective maxima has allowed for not only a continuation
of the previous SLGT risk positioned across the Mogollon Rim in AZ,
but also an expansion further northwest and north, including the
addition of Flagstaff proper. 00z HREF at the end of its temporal
range signaled widespread thunderstorm genesis over the terrain
after 20z Wednesday with some formidable heavy rain cores likely to
materialize out of the initiation. Modest neighborhood
probabilities for >1" of rainfall exist in the small window between
18-00z Wed/Thu with the highest probs situated in that terrain area
between Phoenix and Flagstaff within the Mogollon Rim across
central AZ. In coordination with the local Flagstaff WFO, have
expanded the previous SLGT risk forecast to areas northwest of
Flagstaff within the western periphery of the Mogollon Rim, as well
as a further north expansion to include Flagstaff proper given the
recent trends in guidance, and the premise of urbanization factors
providing more suitable ground conditions for flash flood
prospects.

...Lower Mississippi Valley into Southeast...

Our meandering upper level disturbance will continue to churn over
the Southern U.S. with sights on the Lower Mississippi Valley by
Wednesday afternoon. Models are within close proximity of each
other on the positioning of the disturbance with the centroid of
the circulation likely to be focused somewhere over Arkansas and
the southwest corner of TN. Elevated moisture and general diurnal
destabilization across the Lower Mississippi and Southeastern U.S.
will lead to another round of slow-moving thunderstorms capable of
producing locally heavy rainfall with rates of 2-3"/hr likely in
those stronger cell cores. The setup is not as prolific within the
QPF means compared to the previous few periods, so the threat
remains within the MRGL risk threshold. However, will continue to
monitor trends closely as we move forward in time as the chance for
a targeted upgrade, likely underneath the upper level disturbance,
is plausible.

Kleebauer
 

Day 3
Valid 12Z Thu Jul 16 2026 - 12Z Fri Jul 17 2026

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

...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. There is some uncertainty on
the exact location of the final convective wave that will transpire
with some guidance positioning the greatest threat a little further
north of the area likely to see the greatest impacts from the prior
periods. In any case, the threat is still very much robust for
wherever this transpires as the axis of heavy rainfall will likely
produce more 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.
There's enough of a signal to warrant an addition of a MDT risk
across the area between the Big Bend 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. Considering the nature of the situation, this
period will be monitored very closely and its susceptible to larger
scale changes as the setup evolves. Heavy rain will likely enhance
life-threatening flash flooding to portions of the region for yet
another period before the setup finally looks to break after the D3
time frame.

...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. Ensemble bias
corrected output is 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 0.75-1.25" 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 introduced 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" within the ensembles.

Kleebauer
 

Day 4 and Day 5

Valid 12Z Fri Jul 17 2026 - 12Z Sun Jul 19 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHWEST ON FRIDAY...

...Western U.S...
A broad active monsoonal pattern will continue across much of the
western U.S. Friday into Saturday. 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 eastern CA, AZ, and NM
northward to MT.

We did go ahead and upgrade much of AZ into southwest UT and
southwest NM into a Slight risk for D4 (Friday). While the
prolonged monsoonal pattern will bring at least a localized flash
flood threat to the region each of the next 5 days, current model
guidance indicates Thursday and Friday will see a peak in both PWs
and CAPE. Model consensus and NBM QPF are also higher on these
days. Of course, mesoscale details (which we can't pin down at this
lead time) may end up determining the eventual flash flood
coverage. But there seems to be enough of a signal to suggest the
risk may be relatively higher those two days. The isolated threat
continues into D5 (Saturday), but will hold that at a Marginal for
now with a modest decrease in PWs/CAPE/QPF noted in the models
compared to Friday.

...Texas...
The multi-day heavy rainfall event over portions of central and
west TX should be on a declining trend by Friday. PWs gradually
decrease and lower level convergence seems to wane, with both the
AI models and GFS/ECMWF showing a decrease in convective coverage.
With that said, we will still have strong 850mb southerly moisture
transport across the state, and some leftover shortwave energy. So
the event is likely not over on Friday, just probably less
widespread and hopefully not as high end. The setup into Friday is
still favorable enough that can not rule out Slight risk upgrades
on future updates, especially if the convective footprint overlaps
hydrologically sensitive areas from previous rainfall. The risk
should lower further by Saturday, but again some risk of a locally
heavy rainfall threat continues from the Edwards Plateau and points
west.

...Great Lakes into the Mid-Atlantic...
On Friday a Marginal risk was introduced from portions of the TN
Valley northward into the Great Lakes. The strong mid to upper
level ridge currently anchored over the Plains/Midwest is forecast
to break down and translate southeastward. This synoptic shift will
allow the high PW airmass currently situated over the South to
advect north-northeastward. By Friday afternoon much of the OH and
TN valleys will have PWs around 2" and CAPE potentially exceeding
3000 J/kg in spots. This unstable and saturated environment will be
conducive for high rainfall rates. While weaker large scale
forcing across the southern portion of the risk area may limit
overall convective organization isolated instance of flash flooding
will be possible. Further north, stronger synoptic forcing should
support organized convection across portions of WI into northern
MI. These convective cluster may lean toward a progressive mode,
but the degree of instability and PWs should support some flash
flood risk.

On Saturday the core of the high PW airmass shifts eastward into
the Mid-Atlantic. Amplifying troughing building into the
Northeast, accompanied by embedded shortwave energy, should
support a organized convective threat from OH into the northern
Mid-Atlantic and possibly southern NY. 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. 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.

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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