FOUS30 KWBC 230811
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Wed Jul 23 2025

Day 1
Valid 12Z Wed Jul 23 2025 - 12Z Thu Jul 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST...

...Upper Midwest...

Increased confidence in heavy rainfall is forecast across a good
portion of the Upper Midwest with the latest 00z HREF mean QPF
distribution heavily focused over east-central MN across into
northern WI and the western Michigan U.P through the period.
Expectation is for an initial round of convection forming upstream
over the Dakotas into northwestern MN, migrating east-northeast
within the general mean flow the first 6 hrs of the forecast, a
carryover from the previous D1. Isolated flash flood prospects 
will be feasible during this initial wave of precip, but the 
pattern takes a turn for potentially higher impacts as the surface 
cold front to the north begins pressing further southeast through MN/WI.

Expecting a secondary cluster of thunderstorms to develop 
over south-central MN up into northern WI in the early afternoon 
hrs., spurred on by a strong theta_E advection regime forming along
and south of the cold front as it begins to fan out more west- 
southwest to east- northeast once down near the latitude of 
Minneapolis-St. Paul. 00z CAMs are bullish on a broad development 
of heavy thunderstorms within the confines of the front with 
relatively slow cell motions thanks to the mean flow aligning 
parallel to the boundary. A deep moisture presence running between
2-3 standard deviations above normal and wet bulb zero heights 
between 13.5-14k ft MSL will enable more efficient warm rain 
processes with embedded convective element, an environment 
suitable for rainfall rates between 1-3"/hr with some intra-hour 
rate potential >4"/hr at times as signaled within some of the 
individual deterministic. HREF neighborhood probabilities took a 
larger step into more robust depictions of the potential with the 
latest >3" signal now firmly between 50-70% from east-central MN 
across into north-central WI. This alignment also includes the 
greater Minneapolis metro and areas along and north of I-94 within 
both MN/WI. This area is one of the more prone spots in the 
northern CONUS for flash flooding due to the urban footprint and 
locally higher run off capabilities. This signal is prevalent for 
much of northern WI with convection basically aligning downstream 
and prevailing through much of the afternoon and evening before the
front finally sweeps through and carries the threat more into WI 
and the Michigan U.P. 

There's growing concern of the upstream evolution also becoming
more suitable for widespread convective development generated by
the ejection of a stronger mid-level shortwave into the Central
Plains providing ample ascent within the diffluent area downstream
of the mean trough. CAMs are in and out on the proposed convective
evolution, mainly spatial coverage with some of the CAMs very
bullish which would exacerbate precip potential downstream over NE
into southeastern SD and southern MN/northern IA. This is setup can
tough to figure out at leads, but the mass fields involved are very
much capable of producing a secondary area of heavy precip, even
bordering on significant if you believe some of the hi-res deterministic.

Overall, the combination of favorable thermodynamics and upper
forcing brought on by right-entrance region dynamics from a
strengthening upper jet over Canada will combine to produce
widespread heavy rainfall with a lean towards locally significant
impacts, especially along and north of the I-94 corridor. Totals
between 2-4" with locally as high as 6" are forecast within the
Upper Mississippi Valley up towards the shores of Lake Superior. As
a result, a high end SLGT is forecast from south-central MN and
points northeast, including; Minneapolis/St. Paul, Duluth, Eau
Claire, and the western Michigan U.P. SLGT risk encompasses much of
the Upper Midwest, extending back to the southwest through parts of
the Central Plains thanks to the prospects of a secondary heavy
convective episode that could very well gain more traction as time moves on.

...Florida and the Coastal Southeast...

The active pattern across the Southeast CONUS will continue through
Wednesday with a generally smaller convective footprint compared to
the previous period, but enough to warrant a continued MRGL risk
for locally heavy rainfall. Weak upper trough carrying a formidable
tropical airmass will pivot eastward along the Central Gulf coast
leading to PWATs encroaching 2.25-2.5" consistently from LA over
into the northern half of the FL peninsula. Ascent pattern is
fairly tame with the lack of sufficient jet dynamics, but the
combination of a weak surface reflection migrating southwest from
off the GA coast into the northeast portion of the Gulf will aid in
some enhanced low-level convergence capable of heavy convection
firing and maintaining foothold over places like the northern FL
peninsula and along the immediate Central Gulf coast. Signals are
relatively weak for prospects of >5" (<20%), but there is a decent
enough threat for upwards of 5" which is more than feasible 
considering how little effort it will be for any convective 
elements to produce 2-3"/hr rates given the favorable buoyancy and 
deep moisture presence. Any cells that train or hold ground for any
length of a few hrs. could spell for locally significant rainfall 
which could induce flash flood concerns, even away from urban 
centers. The previous MRGL risk was maintained with only minor adjustments.

...Central and Southern Rockies into High Plains...

Another active period on tap with scattered to widespread
convective development anticipated across the Central and Southern
Rockies through the adjacent High Plains on Wednesday afternoon and
evening. PWATs remain very high (90-97th percentile according to
NAEFS anomalies) across the central High Plains with a bit less a
deep moist axis in-of the Rockies. Even with the less emphatic
signature over the terrain, a slew of smaller mid-level
perturbations within a shortwave trough located over the Front
Range, as well as increasing upper ascent ahead of a deeper upper
trough centered off CA will allow for ample convective initiation
across NM up into CO with a consensus on the greatest coverage
along the Continental Divide. The aforementioned shortwave over the
Front Range will be the disturbance that kicks off yet another
convective cluster over northeast CO with advancement to the
northeast as it follows the mean flow. A relatively good agreement
on a regional max over that area of northeast CO into southern NE
with neighborhood probs running between 40-70% for at least 2" in
this corridor. FFG's in these areas are somewhat high compared to
areas well downstream, so the ability to take a decent hit of heavy
rainfall is better leading to lower chances for widespread flash
flood prospects. Still, it's an area to monitor for short term
upgrades if the signal becomes more prolific for higher totals. NM
coverage will be less than the previous period, so isolated to
widely scattered flash flood concerns lean more to a broad MRGL
risk as well with the extension into CO. 

Kleebauer


Day 2
Valid 12Z Thu Jul 24 2025 - 12Z Fri Jul 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
PLAINS INTO THE MIDWEST...

...Central Plains to Upper Midwest...

The previous forecast maintains a consistent signature for heavy
rainfall in-of the Central Plains up through portions of the
Midwest. The pattern is being driven by stout ridging over the
Southeastern CONUS extending up into the Mississippi and Ohio
Valleys with a cold front gradually gaining latitude as it pushes
through the Plains and Midwest. Frontal positioning and very
anomalous moisture (PWATs between 90-99th percentile according to
the latest NAEFS) will aid in the persistence of heavy convection 
developing and training within the confines of the front leading to
rainfall totals locally exceeding 3" in areas from KS up through
the southwest side of Lake Michigan. There's a growing consensus
within the ensemble means of the corridor of heavy precip generally
aligned southwest to northeast where the front will be located, a
classic signature for training given the expected mean flow to be
parallel to the front for a majority of the period. 00z EC AIFS
ensemble has continued to trend upward in its mean QPF output
across KS into MO where the deepest moisture presence is noted as
>2" PWATs are running between 80-100% in the prob fields from all
three HREF/ECENS/EC AIFS Ens. from central KS up through
northwestern MO. This is the area of greatest concern for highest
totals due to the environmental factors at play with rates likely
to top 2"/hr in the strongest convective cores during the period.
Enough of a signal was present to extend the SLGT risk further
southwest to account for the better probabilities for >1" within
the ensemble with a continuation of the SLGT to the northeast as
heavy rain is likely to occur over northern IL towards the
Chicago/Milwaukee corridor. 

...Central High Plains and Central and Southern Rockies...

Isolated to widely scattered convection will initiate, once again
across the Front Range back into the Central and Southern Rockies
with localized maxima likely contributing to a few flash flood
prospects in their wake. The primary ascent is still within that
diffluent area ahead of the closed reflection over CA through the
forecast period. Enough of a deep moisture presence and modest
instability up through the Continental Divide and points east will
be suitable for another day of convection with the best opportunity
for flash flooding likely located in proximity of the complex
topography centered over northern NM through CO and southeast WY. A
MRGL risk was relatively unchanged from previous forecast
highlighting the threat. 

...Southeast...

The presence of a slow-moving surface reflection and eastward
progressing upper trough across the northern Gulf will lead to
another period of heavy rainfall within the confines of the
Southeast CONUS. Greatest opportunity will lie along the central
Gulf coast where the proximity of the surface low and attendant
surface trough could allow for short periods of convergence in-of
areas along and south of I-10 from LA back into the western FL
panhandle. Guidance remains inconsistent on any organized
convective placement with a smattering of heavy QPF bullseyes
anywhere along the Gulf coast with even some extending back up
through the GA and portions of the Carolina's. With PWATs remaining
up inside the 90-99th percentile along the immediate coast and
suitable instability presence, the previous MRGL was maintained
with general continuity.  

...Northern California and Adjacent Areas...

A narrow tongue of elevated moisture on the northern periphery of a
closed upper reflection along the CA coast will lead to a period of
convective development within the northern Sierra's through
northern CA and southern OR. PWATs running ~1 standard deviation
above normal and MUCAPE between 500-1000 J/kg should be sufficient
for scattered convective initiation along the ridges which could
easily produce local 1+" of precip in a short time. Given the
favorable pattern into the terrain still dealing with remnant burn
scars and complex drainage, the risk for at least isolated flash
flooding still has merit. The previous MRGL risk was generally
maintained with only minor adjustments. 

Kleebauer


Day 3
Valid 12Z Fri Jul 25 2025 - 12Z Sat Jul 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST AND OHIO VALLEY...

...Midwest and Ohio Valley...

Persistence within the upper pattern and a slowly trudging cold
front over the Midwest and Ohio Valley will lead to yet another
period of heavy convective development across the Mid-Mississippi
Valley to points east, mainly in the confines of the front. General
consensus within the means on there being a more defined convective
element over IL through IN and western OH on Friday into possibly
early Saturday morning. A sheared mid-level vorticity maxima is
forecast to meander over the region with the frontal positioning
likely the focal point for convective development/maintenance.
Surprisingly, there is a pretty good signal in the global
deterministic for between 2-4" of rainfall in spots within the
above area, but the placement of course is subject to the exact
frontal positioning. The greatest moisture anomalies between 2-3
deviations above normal will likely be centered in-of the Ohio
Valley with the maxima somewhere along I-80 and points north when
looking at ensemble depictions and various ML. The environment will
be more than capable of continuing the theme of higher rates
between 2-3"/hr at times, so any training could spur flash flood
concerns during any time frames of impact. First Guess Fields have
a SLGT risk situated over IL into IN for the D3, aligning well with
the current proxy of highest QPF being forecast in the means. This
was enough to warrant a SLGT risk upgrade from the Mississippi
Valley over into portions of the Ohio Valley.

...Gulf Coast...

Our disturbance across the northern Gulf will continue to slowly
migrate to the west with an attendant surface low remaining
situated just south of the west-central Gulf coast. Low center
proxy will be the ultimate factor in the prospects of very heavy
rainfall along the immediate Upper TX coast back into LA. So long
as the low center remains far enough offshore, the greatest low-
level convergence pattern and persistent area of convection could
remain just off the coast to limit impacts. However, the airmass
surrounding the disturbance will still be pretty robust with PWATs
remaining very high (>2.3" for much of the immediate coastal plain
over TX back through the central Gulf coast. The National Hurricane
Center has introduced a 10% within the latest Tropical Weather
Outlook over the northern Gulf for the next 3-5 days, so any
tropical characteristics from this disturbance could enhance flash
flood prospects further, especially when it moves closer to the
Upper TX coast. For now, a broad MRGL where PWATs remain high and
ensembles indicate some convective posture is in effect as we keep
a watchful eye on the threat. 

...Northern Plains...

A quick moving shortwave ejecting out of the Rockies is forecast to
impact the Northern Plains on Friday night into early Saturday with
scattered thunderstorms likely to roll through the Dakotas after
sunset. Increased regional PWATs upwards of +2 deviations along
with ample mid-level forcing will be enough for a period of
enhanced heavy rainfall prospects during the time frame of impact.
Deterministic output is all over the place in exact convective
placement and magnitude, however signals for 2-4" of rainfall in a
short period of time would be sufficient for at least low-end MRGL
prospects up across parts of the Dakotas. Timing of the shortwave
will be key for the threat, but there was enough consensus on their
being a chance for a maintenance of the MRGL risk inherited.

Kleebauer
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