Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Thu Jul 9 2026

Day 1
Valid 12Z Thu Jul 09 2026 - 12Z Fri Jul 10 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE CENTRAL HIGH PLAINS TO THE MID-ATLANTIC...

...Mid-Atlantic...
Moisture and instability will increase today ahead of a mid-level
shortwave tracking through the area during peak heating. PW values
are forecast to exceed 2" alongside SBCAPE over 2000 J/kg, a
favorable profile for heavy rainfall rates. While convection is
expected to eventually consolidate into a forward propagating
convective line or cluster, scattered thunderstorms should develop
initially from northern VA into southeast PA. Cell mergers are
possible with this initial activity and as the upstream convective
line/clusters arrive.

With both the REFS and HREF showing locally heavy rain and 15%+
FFG exceedance probabilities, the Slight risk was expanded
westward into more of southern PA and portions of WV. The highest
EAS probabilities from the HREF/REFS point to an axis across
northeast MD, southeast PA, southern NJ and DE as the most favored
corridor for concentrated heavy rainfall. Neighborhood
probabilities from both ensemble suites indicate a 50-80% chance of
locally exceeding 3" of rain, a 15-30% chance of exceeding 5", and
a 30-50% chance of 2"'hr rainfall. Given the impressive CAPE/PW
overlap, wherever clusters manage to merge and briefly train, some
flash flooding is likely and consider this a higher end Slight
risk. Locally significant urban flash flood impacts are possible
if heavier cells end up over a sensitive urban location.

...Mid MS Valley into the OH Valley...
Morning convection moving across MO is expected to weaken, however
robust redevelopment is expected by this afternoon ahead of a
shortwave extending from MO into IL. While cells should generally
remain progressive as they track eastward, brief cell mergers could
locally elevate the flash flood threat. The 00z HREF and REFS are
in good agreement that southeast MO, southern IL and western KY
will see the most concentrated heavy rainfall axis. As a
strengthening low level jet boosts moisture transport this
evening, the southern tail of the convective line may hang up,
allowing for a period of backbuilding and training. HREF/REFS
neighborhood probabilities show a 40-70% chance of rainfall locally
exceeding 3" along this axis. Scattered flash flooding appears
likely given this setup, although just enough southward propagation
of convection may cap rainfall totals and keep the flash flood
risk from being even higher.

...Central High Plains...
Mid-level shortwave energy combined with upper jet support will
produce convection across the High Plains from CO to SD this
afternoon. Deep layer shear and instability should be sufficient to
support slow moving supercells capable of pockets of intense
rainfall and localized flash flooding. With storm motion vectors
quite weak, most high res models seem too quick in moving this
activity off to the east (a common bias). Convection will
eventually shift east by tonight, and a majority of the 00z high
res models support some upscale growth as it moves into western and
central KS. Portions of eastern CO, southwest NE and
western/central KS have been upgraded to a Slight risk with
isolated to scattered flash flooding possible.

...Arizona...
Convection developing over the higher terrain may propagate
southwestward into the lower deserts during the late afternoon and
evening hours. Uncertainties persist regarding storm propagation
speed (whether cells will move too quickly to produce any
flooding) and the exact spatial extent/magnitude of instability.
While the overall threat looks more robust later this week into
the weekend, we will maintain the inherited Marginal risk.

Chenard


Day 2
Valid 12Z Fri Jul 10 2026 - 12Z Sat Jul 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE MID MISSISSIPPI VALLEY INTO THE CENTRAL APPALACHIANS...

...Mid MS Valley to the Central Appalachians...
A favorable environment for convective training and backbuilding
should take shape across portions of the OH and TN valley on
Friday. Multiple shortwaves embedded within the west to northwest
flow aloft will interact with a persistent westerly low level
moisture transport vector. This wind profile will result in very
weak Corfidi vectors, and thus upwind propagation and backbuilding
into the low level flow is probable. This setup will overlap an
unstable and moist airmass, with PWs forecast around or over 2".

Some uncertainty remains regarding convective evolution,
especially how morning convection affects afternoon
destabilization and exactly where the instability axis recovers
and sets up. There are also some differences in the
strength/timing of the convectively enhanced shortwave that will
be tracking into the area from the west. The current model
consensus consisting of the ECENS/GEFS/AIFS/AIGFS favors much of KY
into northern TN for the axis of heaviest rain. A higher end
SLight risk will cover these areas, with the caveat that the exact
axis will likely require some spatial adjustments in future
updates. Will need to continue to closely monitor the evolution of
this threat, as a setup such as this could result in an eventual
MDT risk pending model trends.

...High Plains...
Additional shortwave energy ejecting out of the Rockies will
trigger another round of convection from the TX Panhandle into CO
and KS. The low level jet and overall forcing may be a bit weaker
than Thursday, which may limit the degree of organization and
upscale growth. Nonetheless, some slow cell motions and high
rainfall rates will maintain a threat for localized flash flood
impacts.

...Arizona...
The synoptic and mesoscale setup on Friday will be very similar to
day 1, although instability maybe slightly higher. Both the RRFS
and REFS depict more robust convective development capable of
producing localized rainfall totals over 2 inches. While this risk
should remain isolated, the flash flood threat appears slightly
higher than on Thursday.

Chenard


Day 3
Valid 12Z Sat Jul 11 2026 - 12Z Sun Jul 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE OHIO/TENNESSEE VALLEYS AND CENTRAL APPALACHIANS...

...OH and TN valley...
The favorable heavy rainfall pattern will persist into Saturday
across portions of the OH and TN Valley. Deep layer westerly flow,
persistent low level moisture transport, and weak Corfidi vectors
will support the potential for training/backbuilding cells. While
convective scale details remain uncertain this far out, large
scale forcing will be strong, with a well defined mid level
shortwave diving southeast into the region beneath the right
entrance region of an upper level jet streak.

Organized convection within an airmass characterized by PWs around
2" will support heavy rainfall rates. Given the potential for
training and backbuilding in this environment, some flash flooding
again appears likely. The exact heavy rainfall axis is unclear and
will depend on leftover mesoscale boundaries and the exact
strength/track of the shortwave, but an area from TN and KY into WV
appears most at risk. This is a solid Slight risk, with isolated
to scattered flash flooding expected. If this axis ends up
overlapping with heavy rainfall from day 2, then a higher risk
category may eventually be required.

...Southwest...
The terrain driven convective pattern will continue across AZ,
with storms rolling off the terrain and into an instability pool
over southern AZ. Both instability and PWs should be higher
Saturday than prior days, which should drive greater convective
coverage and at least isolated flash flooding. Trends will be
monitored, with a Slight risk upgrade in future cycles a
possibility.

Chenard


Day 4 and Day 5
Valid 12Z Sun Jul 12 2026 - 12Z Tue Jul 14 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS, MID/LOWER MISSISSIPPI VALLEY, TENNESSEE
VALLEY, SOUTHEAST AND THE MID-ATLANTIC...|

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
ARIZONA AND NEW MEXICO...

A frontal boundary will be advancing southward through the Midwest,
Tennessee Valley and Southeast which will be a focus for scattered
convection Sunday and Monday. Any of these thunderstorms have the
potential to produce pockets of heavy rainfall that could lead to
isolated instances of flash flooding. A Marginal Risk was
maintained for the Sunday from eastern Texas and Oklahoma to the
Mid-Atlantic and Southeast, while a new Marginal Risk was raised
for the Gulf Coast and Southeast for Monday.

Increasing southerly flow around the western periphery of the
central U.S. ridge will draw monsoonal moisture into the southern
Four Corners and Great Basin later this weekend into early next
week. This moisture will likely lead to the development of
scattered to numerous showers and thunderstorms with the potential
to produce heavy rainfall and localized flash flooding. A Marginal
Risk is in effect for portions of Arizona and New Mexico for both
Day 4 and Day  5.

Campbell


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt