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
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