FOUS30 KWBC 290041
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
841 PM EDT Tue Jul 28 2026

Day 1
Valid 01Z Wed Jul 29 2026 - 12Z Wed Jul 29 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHEAST...

...Mid Atlantic and Northeast...

01Z Update: The current forecast Moderate Risk remains on track
across the Mid Atlantic and Northeastern U.S. with heavy rainfall
and several flash flood warnings ongoing at this hour. SLP over the
central Mid Atlantic will continue to make headway towards the
coast with the center of circulation likely to settle south of LI
by the morning. Upper pattern will eventually close off over NY
state into Northern New England, taking on a more neutral to
negative-tilt as it evolves. This will allow for heavy rain to
pivot over the Lower Hudson into Southern New England as flow
becomes increasingly backed and precip likely exhibits more
training potential in the vicinity of the Lower Hudson into western
MA along the Berkshires. In this setup, it is likely for
significant rainfall to occur with most deterministic inferring
potential for >4" of additional rainfall in the hardest hit areas.
Considering the general consistency in the hi-res CAMs, elected to
maintain continuity with the MDT risk to ensure the setup being
covered and to convey consistent messaging with local WFO's
impacted.

Kleebauer

..Previous Discussion..

There will be a transition in the convective pattern as we reach
the overnight hours. A strong mid-level vort max, very evident in
GOES East satellite channels across north-central Pennsylvania, is
likely to induce the development of a surface low somewhere over
the region. The position of this surface low will be critical to
where the threat of flash flooding maximizes during the overnight
period and as we approach 12Z (and the morning commute). Our best
estimate is that this would be favored just southeast of the
current trajectory of the surface low, and near the largest
concentration of afternoon convection. For now that looks like it
will be somewhere from SE PA to C NJ by the 00-06Z time frame, and
lifting northeast toward S NY and CT by 06-12Z. This is where the
latest 14Z HRRR places it, and is consistent with the ECMWF
Ensemble and AIFS/AIFS Ensemble. However, there is still
considerable uncertainty. The reason the position of the low is
important is that instability should decrease while PWs stay quite
high, favoring low-topped and very efficient convective rain bands,
and these would tend to concentrate near and just north/east of the
surface low in an area of maximum mesoscale forcing and low-level
convergence. There are also signs that rain bands will extend north
along an inverted trough, perhaps well up the Hudson Valley and
into Vermont. While the maximum rain rates may slightly decrease
during the overnight period, more into the 1-2 inch per hour range
in the strongest convective bands, there would be greater potential
for persistence, and thus locally extreme rainfall will still be
possible -- the threat will just shift more into far southern and
eastern New York, Long Island, Connecticut, western Massachusetts,
and southern Vermont. It's possible there will be an ongoing rain
band with active flash flooding around the end of the period and in
the transition to Day 2, around the time of the Wednesday morning
commute, particularly from Long Island north into Connecticut and
western Massachusetts.

Taylor

...Central and Southern Appalachians and Virginia...

01Z Update: Removed a large portion of Southwest VA from the MRGL
as rainfall threat over the region remains unlikely, or is subject
to little offering for flash flooding. Quick-moving vort max at the
base of the mean trough continues to press southeast out of the
Tennessee Valley. A line of thunderstorms is likely to maintain
headway into SC/GA through the first part of the evening before
dissipating allowing a maintenance of the MRGL risk across the
Southern Appalachians. A few hours exist for heavy rainfall across
the Southern Delmarva into the VA Tidewater, but threat should
dwindle after 04z across the entire area. Fast cell motions should
limit the extent of any flash flood risks, but some of the more
complex terrain in the Southern Appalachians could see an isolated
instance of flooding considering rates between 1-2"/hr prevalent in
the cells moving over the area.

...Four Corners States...

01Z Update: Scattered bouts of heavy rain will continue for at
least the next 3-6 hours across the Southwest with the heaviest
rainfall concentrating over the Front Range of CO thanks to the
influence from a stronger mid-level shortwave ejecting out of the
Rockies. Several flash flood warnings remain in effect in the
terrain from CO into NM and AZ. Models indicate local pockets of up
to 1" across portions of AZ and NM, but upwards of 2-3" possible
over the Front Range of CO up into southwestern NE. The previous
SLGT risk was generally maintained, but extended a bit further
north into NE to account for current heavy convection in the area.
Also trimmed out portions of AZ (Central Mogollon Rim) as rainfall
chances in the area are have likely subsided for the rest of the
period with only an isolated cell or two plausible to the northwest
of Flagstaff.

Kleebauer


Day 2
Valid 12Z Wed Jul 29 2026 - 12Z Thu Jul 30 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHEAST...

...Northeast...
Intense rainfall, some of which will be training and repeating, is
expected to be ongoing at the start of the Day 2 period Wednesday
morning, particularly across western MA, far southern VT, and
broadly across southern New England. Rainfall rates between 1-2"/hr
at times will be possible through late morning/early afternoon and
totals of 2-4" (with localized higher amounts possible) are
expected. HREF neighborhood probabilities remain high (greater
than 80 percent) for 3" totals across western/central MA into far
southern VT. Probabilities are moderate (30-50 percent) for 5"
totals.

Given the setup and risk of significant flash flooding continuing
from the day 1 period, a Moderate Risk has been introduced for the
day 2 period, mainly to account for what is expected to be ongoing
in the early part of the period. The second half of the period
(after 00Z Thu), the intensity of rainfall should subside while
also shifting eastward.

...Four Corners States into the Central/Northern Plains...
Monsoonal flow persists with isolated to widely scattered
convection extending from the Four Corners region north and
eastward...perhaps extending as far east as the plains of Colorado.
Some of this rain could fall atop soils saturated from heavy rain
on Tuesday and Tuesday night. Overall, the risk area remains in
good shape with the Slight Risk focused on eastern Colorado.

...Central Gulf Coast Region into parts of the Southeast...
A cold front stalling along the Gulf Coast will be a focus for slow
moving and training thunderstorms on Wednesday. Guidance continues
to indicate a low-probability threat for at least 3" of rain due to
training of 1-2"/hr rain rates within favorable thermodynamics.
This region can generally tolerate significant rain rates and this
amount of rainfall, but any more pronounced training could result
in isolated flash flood related impacts.

Taylor/Bann/Weiss


Day 3
Valid 12Z Thu Jul 30 2026 - 12Z Fri Jul 31 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEY...

...Lower Missouri Valley into the Mid-Upper Mississippi Valley...
Shortwave energy will be progressing east southeast as it tracks
across parts of the central and northern plains on Thursday into
Thursday night/early Friday morning. The shortwave energy will be
encountering an increasingly moist and unstable airmass with
precipitable water values in excess of 2 inches being drawn into
the region ahead of the shortwave. Given the MCS/upscale growth
potential with this system, concentrated areas of heavy rain are
expected, especially across the Corn Belt. The Slight Risk is in
good shape and covers the ensemble guidance and uncertainty/spread
among the models.

...Four Corners States into the Central/Northern Plains...
Monsoonal flow and anomalous deep-layer moisture will maintain an
isolated excessive rainfall risk extending from eastern Arizona
northeastward across much of western and northern New Mexico into
parts of Colorado. The expanding mid/upper level ridge will likely
limit the coverage compared to recent days.

...Central Gulf Coast Region into parts of the Southeast...
Heavy rainfall is expected along a front associated with a low
pressure system which will be pulling away from New England.
Heavy rainfall with some potential of flooding will be focused
along and near the front...especially over parts of Florida and
Georgia line.

...New England...
The departing low pressure is expected to be across eastern MA at
the start of the period and transition off the coast during the
period. Locally heavy rainfall will remain possible across the
region given its proximity and ample moisture to work with. While
the instability will likely be less compared to Tuesday/Wednesday,
the stronger dynamics at play and potential for training rainfall
could lead to a localized threat, particularly if over areas more
saturated from previous rainfall. A Marginal Risk was added.

Taylor/Bann


Day 4 and Day 5

Valid 12Z Fri Jul 31 2026 - 12Z Sun Aug 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS
PARTS OF THE MID AND UPPER MISSISSIPPI, AND ON SATURDAY OVER
PORTIONS OF THE LOWER OHIO VALLEY, TENNESSEE VALLEY, AND DEEP
SOUTH...

20Z Update: Previous forecast and synopsis on the upcoming pattern
remains prevalent and consistent with regards to run-to-run
continuity. Biggest adjustment for the D4 was a minor expansion to
the east over southern WI and northern IL for the SLGT risk as
ensemble mean QPF >1" saw a small shift in that direction in the
12z NWP suite. This correlates favorably with the EC-AIFS QPF
alignment which is even further east than what is currently
forecast as the heaviest QPF is even east of the Mississippi around
IA/IL. Didn't want to engage in that large of a shift, so split the
middle and correlated the SLGT risk with the PQPF >1" probability
that was greater than 30%, a threshold that typically favors more
of a SLGT risk opportunity for the D4 period.

The D5 saw an adjustment of the SLGT risk further to the N/NW over
IL/IN as the upper level progression from our shortwave over the
Upper Midwest will play a significant role in where there will be
not only sufficient convective coverage, but also focusing an area
where training/repeating cell development could play a greater role
for flash flood prospects. There's a general consensus on the
primary circulation aloft cutting through IL and potentially
closing off somewhere over eastern IL down towards the western Ohio
Valley. Some of the deterministic is pretty aggressive in their QPF
presentations, mainly the models that show that earlier closed 5H
signal. In this case, enough merit with the ensemble QPF increase
in the region to to move the SLGT a bit further N/NW to account for
the trend.

There were no significant changes to the MRGL risk outlines across
the Southeastern U.S. and the Southwestern U.S. with their
respective patterns as the QPF forecast remains pretty consistent
across the Central Gulf Coast into FL.

..Previous Discussions..

...Mississippi Valley-Ohio Valley-Tennessee Valley-Deep South...
On Day 4 (Friday-Friday night), minor changes were made to
yesterday's Day 5 ERO, including refinements to the Slight Risk
area over parts of the Mid-Upper MS Valley, based on the latest
(00Z) global deterministic and probabilistic QPFs. The operational
models continue to show max 24hr totals in the 3-5" range,
particularly over IA-southeast MN-southwest WI, though again with
some spatial spread in the guidance. 00Z Operational ECMWF has a
bit more areal coverage of the 3+ inch totals, while the ECENS QPF
exceedance probabilities have once again come up from the previous
run. Based on the latest guidance, along with the most recent ECMWF
EFI output (EFI values aoa 0.6), have nudged the southern portion
of the Slight Risk area a little farther north across the Mid MS
Valley.

On Day 5 (Saturday-Saturday night), the globals continue to show a
fairly vigorous 500 mb trough/embedded shortwave energy slowly pivoting
into the Mid MS Valley. There isn't as strong of a signal in the
QPF guidance compared to the previous couple of days; however, the
amplifying upper level trough (favorable Qs forcing and increasing
effective bulk shear) will combine with a favorable thermodynamic
profile (ML CAPEs 1000-2000 J/Kg along a swath of 1.8-2.1" PWs) to
generate organized heavy rainfall threat across western portions
of the Lower OH Valley into the TN Valley and perhaps as far south
as southern AL, depending on how far south the upper shortwave and
favorable 0-6KM bulk shear can get. Concern within this area will
be heavy rainfall rates (2+ in/hr) given the thermodynamic profile,
along with the potential for cell training of convection as the
upper shortwave begins to stall and the low-level inflow out ahead
of it increases up and aligns more parallel to the mean 850-300 mb
flow. Because of these factors, we felt that a Slight Risk was
warranted.

...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 much of CO. The expanding mid/upper level ridge
(600dm heights at 500 mb) will likely limit the coverage compared
to recent days, especially on Friday.

...Central Gulf Coast Region into parts of the Southeast...
Heavy rainfall is expected along the New England cyclone's trailing
front near the FL/GA border, the front that will become more
quasi-stationary Thu-Fri before lifting lifting back north on Sat
ahead of the approaching upper trough. 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, have maintained the inherited Marginal Risk on Day 4 (Fri-
Fri night), with a similar Marginal Risk area on Day 5 (Sat-Sat
night).

Hurley


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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