FOUS30 KWBC 140821
QPFERD

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

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
$$
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