482
FOUS30 KWBC 040031
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
831 PM EDT Thu Jul 3 2025

Day 1
Valid 01Z Fri Jul 04 2025 - 12Z Fri Jul 04 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
TEXAS AND NEW MEXICO...

...Northeast New Mexico into Central Texas...
Radar trends keep northeast NM in the Slight Risk for the time
being, but convection should increasingly focus in the TX Hill
Country/near the Escarpment as outflow boundaries from the east and
north help focus storms with heavy rainfall. Also, the mid-level
remains of Barry appear to have spun up somewhat across the Trans
Pecos which has been apparent in radar imagery late Thursday
afternoon into early Thursday evening. Outflow boundaries should
effectively stall in the near term. Any low- level veering appears
minimal overnight, and mid- level capping is minimal as well. Some
increase in low-level inflow could lead to effective bulk shear ~25
kts which could lead to convective organization. Given
precipitable water values in the 2.25"+ range, this could equate
into hourly amounts to 3" where storms can train, backbuild, or
merge. Across South-Central TX, the 18z HREF signal for 5"+ (over a
small area) and 8"+ (in one spot) through 12z was greater than
50%, which was troubling. Believe this environment is at the high
end of a Slight Risk -- possible localized Moderate Risk impacts
cannot be ruled out should convection persist for several hours.
Convection should continue overnight, feeding on ML CAPE currently
at 1000-3000 J/kg. With this amount of moisture, believe convection
will remain surface based as is typical for warm core lows.


...Wisconsin...
A new Slight Risk was coordinated with MPX/Minneapolis MN, ARX/La
Crosse WI, and MKX/Milwaukee WI forecast offices. There are early
signs of stationary convection across central WI, as well as other
storms trying to move into southwest WI from IA. The region
depicted in the new Slight Risk is along an ML/MU CAPE gradient
within a region of no significant mid-level capping. The 18z HREF
probabilities of 3"+ and 5"+ through 12z were sufficient to elevate
the risk. Effective bulk shear near 40 kts should organize
convection to train along the instability gradient, which could
contain some mesocyclones. Hourly amounts to 2.5" would not be a
surprise given the available moisture and instability, which would
exceed the three hour flash flood guidance. Of special concern
would be if a strong enough cold pool forms which keeps convection
stationary for 3-6 hours to get higher end amounts of 8"+. Local
Moderate Risk- type impacts cannot be ruled out in areas with
prolonged backbuilding or training.


...Eastern Oklahoma to central Louisiana...
A focused area of convergence is expected to continue to have some
threat of heavy rainfall during the overnight hours, as MU CAPE
gradually decreases from 2000+ to 1000+ J/kg while effective bulk
shear is close to sufficient for organization. Given what`s
happened in the area as of late -- especially eastern OK -- will
let the Marginal Risk ride. Hourly rain amounts to 2.5" remain
possible.


...Southeast...
The Marginal Risk area has been constrained mostly to FL to deal
with ongoing convection and early morning Friday convection near
the west-central and southwest FL coasts.


...North Dakota/Northwest Minnesota...
Convection is starting to get going near western ND at the present
time with cell propagation/motion to the northeast noted. The
anomalous moisture presence allows for a bit of a better threat
locally compared to normal. There was also a negligible, yet
existent, chance of 5"+ through 12z, so left the Marginal Risk be,
though it is now merged into the WI risk area.


Roth



Day 2
Valid 12Z Fri Jul 04 2025 - 12Z Sat Jul 05 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
EASTERN NORTH DAKOTA AND NORTHWESTERN MINNESOTA...

...Northern/Central Plains and Upper Midwest...

20Z Update: The SLGT risk across the Northern Plains and Upper
Midwest was maintained, but adjusted a bit further to the east to
account for relevant trends in heavier QPF now positioned a bit
more across North-Central MN. Highest neighborhood probs for >3"
(40-80%) lies on a southwest to northeast orientation from the
ND/SD line between BIS/ABR up through the International border of
MN. Convective scheme is historically proven to skew a bit further
east with cold pool advancement which is one reason we are likely
seeing some adjustment in the CAMs already and is outlined in some
of the ML output. Will keep a close eye on the forecast as some
further adjustments east are plausible, but the consensus should
keep the maxima over the Dakotas and Minnesota pretty similar.

Across NE/KS, another shortwave will eject out of the Front Range
with thunderstorm genesis within the Sandhills of NE. The trend is
for heavy rainfall likely to occur over North Platte to Grand
Island with a trend in convection further east towards the
Missouri River as we step into the back end of the forecast period.
12z HREF EAS probs for >1" are running high between the two urban
centers in NE referenced above with a pretty good signature of
50-70% for at least 1" over the general area northeast of Goodland
through that zone between LBF/GID. This correlates to growing
consensus on heavy rain with prospects for local totals between
2-4" when assessing the deterministic CAMs output and some of the
bias corrected ensemble. The MRGL remains due to higher FFG`s and
some questions on the specifics of the evolution of the
convection, but odds for a targeted SLGT have increased and could
be a focus as we move into the D1.

Kleebauer

..Previous Discussion..

A much stronger signal for heavy amounts and possible flash
flooding is expected to unfold across parts of eastern North Dakota
and northwestern Minnesota late Friday into early Saturday.
Southerly winds ahead of a shortwave trough lifting northeast into
the Northern Plains will support PWs climbing to ~2 inches (+2 to
3 std dev). Storms are expected to develop by late afternoon and
train southwest to northeast ahead of a slowly advancing cold
front. With the HREF indicating that 12-hr amounts (ending 00Z Sat)
are likely to exceed 2 inches in some locations, a Slight Risk was
introduced across parts of eastern North Dakota and northwestern
Minnesota. A Marginal Risk was maintained farther to the south into
parts of the Central Plains where convection developing over the
High Plains during the afternoon is expected to advance more
steadily east, limiting the heavy rainfall/flooding threat.

Pereira

...Southern Plains...

Impacts from the previous period coupled with elevated PWATs
reaching between 2-3 deviations above normal and general diurnal
destabilization will likely lead to another round of scattered
convection capable of at least some localized flash flood prospects
across the Permian Basin over into the Concho Valley and adjacent
Hill Country. Modest probs for locally >2" (40-60%) exist over the
aforementioned areas with the recent hi-res ensemble depicting a
greater threat further west than previously forecast. With the
pattern so meridional, the setup will be harder to break down as it
customary for these regimes this time of the year. The previous
MRGL risk was expanded longitudinally in either direction to
account for the threat.

Kleebauer

...Northern Rockies...

20Z Update: Only minor adjustments were made to the MRGL risk
centered over Big Sky country in MT down through ID/WY. Isolated
heavy thunderstorms could cause some issues within more urbanized
zones and complex terrain aligned over the Northern Rockies. Pretty
solid agreement on guidance with the maxima hovering between 1-2"
with a sharp drop off in neighborhood probabilities for >2"
compared to fairly elevated probs for >1". This is generally
coincident with a MRGL risk for these setups and this is no
different, so maintained relevant continuity given the signals.

Kleebauer

..Previous Discussion..

A Marginal Risk was maintained across parts of Idaho, western
Montana, and northwestern Wyoming, where widespread light to
moderate, with embedded locally heavy amounts are expected. A well-
defined shortwave trough along with fairly anomalous PWs (+1 to 2
std dev) are expected to support locally heavy amounts and an
isolated flash flooding threat.

Pereira

...Florida...

Scattered to widespread thunderstorms will form across the
Peninsula on the 4th leading to fireworks likely from Mother Nature
before we kick off the evening festivities. Some of the heavy
rainfall could be pretty efficient with the environment generally
favorable for local 2-4"/hr rates as PWATs reside between 2-2.4"
along the front hung-up over the Central FL Peninsula. Flow will
run relatively parallel to the stationary front leading to some
storms training over the same areas within proxy to the boundary.
Local totals between 3-6" with max to 8" are possible over the area
generally north of Lake Okeechobee up to about Gainsville. This
includes the Orlando metro, so will be monitoring closely for a
possible risk upgrade, but with guidance struggling mightily to
resolve the pattern and potential for surface low generation near
the FL coast, did not want to upgrade too early and will assess
further. For now, the MRGL risk remains.

Kleebauer


Day 3
Valid 12Z Sat Jul 05 2025 - 12Z Sun Jul 06 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE UPPER MIDWEST AND THE SOUTHEAST...

20Z Update: Little change was necessary for any of the MRGL risk
areas in place across the Upper Midwest and Great Lakes, and across
the Southeast U.S. The Southeast MRGL`s will be contingent on
potential surface low development and/or maturation as that could
allow for focused convergence near the coastal areas of FL/GA/SC
which would enhance the threat of heavier rainfall. This is
depicted within a few of the deterministic, but most of the 12z
suite remains just offshore with the heaviest precip. Until we have
a better consensus, the threat is deemed more MRGL with potential
for upgrades if the synoptic threat materializes and model output
increases in magnitude.

Kleebauer

..Previous Discussions..

...Upper Midwest...
Heavy rain developing Day 2 will continue well into Saturday as the
previously noted shortwave and preceding axis of deep moisture
advance from the Northern Plains into the upper Great Lakes. Model
show PWs at or above 2 inches extending as far north as the
Minnesota Arrowhead and the Michigan U.P. With some signal for
training storms to continue, an upgrade to a Slight across some
parts of the region may be forthcoming if the signal persists and
the models start to show greater agreement.

...Southeast...
With the aforementioned wave expected to move out along the
Southeast Coast, a Marginal Risk was maintained from coastal
Georgia to southeastern North Carolina, where the threat for heavy
rains is expected to increase. A Magical Risk was also maintained
along the west coast of Florida along the trailing inflow and axis
of high PWs.

Pereira


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