FOUS30 KWBC 291137
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
737 AM EDT Wed Jul 29 2026

Day 3  Valid 12Z Fri Jul 31 2026 - 12Z Sat Aug 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS
PARTS OF THE UPPER MIDWEST TO MID MISSISSIPPI VALLEY...

Central US system...
Shortwave energy initially moving eastward out of the Northern
Rockies and adjacent High Plains will be accompanied by showers and
thunderstorms on Friday morning. The flow pattern on the northern
part of the upper high anchored to its west sharpens during the
day...which induces a turn to the south for the northern Plains
system. Tended to follow the numerical guidance for placement of
the Marginal and Slight risk areas where the synoptic scale forcing
is greatest. This necessitated a bit more eastward nudging from
the previous outlook. The southern portion of the Marginal risk
area remained closer to the placement of greater instability which
would support higher intensity rainfall rates. Any downpours across
that region may at least have a chance at challenging the flash
flood guidance. Both the GFS and ECMWF placed their axis of highest
precipitable water (1.8 to 2.2 inches) near the Mississippi River
early in the period which gets deflected towards the Tennessee
Valley by early Saturday morning.

...Central Gulf Coast Region into parts of the Southeast...
Locally heavy to excessive rainfall is possible in proximity to an
east-west oriented quasi-stationary front that had been associated
with a Northeast US cyclone in previous days. Deep-layer moisture
and instability should be more than sufficient and the guidance
shows sufficient effective bulk shear (0-6km magnitudes generally
over 20 kts) for more organized/persistent convective organization.
As a result, maintained the inherited Marginal Risk .

...Four Corners States into the Southern-Central High Plains...
Monsoonal flow and anomalous deep-layer moisture will keep the
potential for isolated instances of excessive rainfall across
portions of eastern AZ and much of New Mexico into Colorado. The
areal coverage may be less than in preceding days given the
expansion of the sprawling upper ridge.

Bann
 

Day 4 and Day 5  Valid 12Z Sat Aug 01 2026 - 12Z Mon Aug 03 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL SATURDAY OVER
PORTIONS OF THE OHIO VALLEY AND CUMBERLAND PLATEAU...

...Ohio and Tennessee Valleys into parts of the Southeast...
On Day 4 (Sat-Sat night), rather significant changes were made to
yesterday's Day 5 ERO, based on the latest guidance trends.
Specifically, the globals and most ensembles show the upper trough
amplifying somewhat with the influx of shortwave
energy/convectively- aided vort lobes dropping southeast. However,
most of the guidance show less amplification compared to last
night's runs, with more of a positive to neutral tilt to the trough
vs. negative. This in turn is allowing for a more progressive
west-to-east shift in the pre- frontal rainfall east of the
Mississippi, supported (perhaps led by) both the GFS and ECMWF AI
models. Therefore the Marginal Risk and encompassing Slight Risk
areas were shifted east as well, with the Slight Risk confined to
mainly the northern areas (OH Valley into Cumberland Plateau) per
the ECMWF and GFS AI trends, along with the highest 24hr QPF
exceedance probabilities per the 00Z ECENS, and where there is a
signal (albeit weak) per the most recent ECMWF EFI. The Slight Risk
is also in an area with comparatively lower 1/3/6 hr FFG vs. areas
farther south.

...Interior Northeast...
Aforementioned longwave 500 mb trough does begin to take on a more
neutral to negative tilt on Day 5 (Sun-Sun night) per both the GFS
and ECMWF. As this occurs, the eastward progression of the
favorable pre-trough/front dynamical forcing and associated
moisture axis (PWs of 1.75-2.00" will begin to slow considerably,
thereby allowing for multiple rounds of moderate-heavy rainfall.
For now, have hoisted a Marginal Risk across this region on Day 5,
as the maximum 24hr deterministic QPFs from the latest global runs
are still (for the time being) under 3".

...Four Corners States into the Southern-Central High Plains...
Monsoonal flow and anomalous deep-layer moisture will maintain a
Marginal (isolated) excessive rainfall risk over eastern AZ and
much of NM into south-central CO on Day 4. By Day 5 (Sun-Sun
night), both the deterministic and probabilistic QPFs per the
global and AI guidance would support a smaller MGNL Risk area.

...Central Gulf Coast Region into parts of the Southeast...
Heavy rainfall threat will continue over this region along the
southern periphery of the full-latitude trough, south of the
quasi-sationary front. Deep-layer moisture and instability should
be more than sufficient, especially when coinciding with the weak
upper forcing (upstream upper trough w/ embedded convectively-aided
shortwaves), for more organized/persistent convective
organization. As a result, have maintained the inherited Marginal
Risk on Day 4 (Sat-Sat night), with a similar Marginal Risk area
on Day 5 (Sun-Sun night).

Hurley
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