FOUS30 KWBC 210812
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 AM EDT Mon Jul 21 2025

Day 2
Valid 12Z Tue Jul 22 2025 - 12Z Wed Jul 23 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTH DAKOTA, MINNESOTA, NORTHERN WISCONSIN, & NORTHWESTERN MICHIGAN...

...Northern Plains/Upper Midwest...

Synoptic scale evolution over the northern tier of the CONUS will 
lead to a continued unsettled weather pattern with another round of
heavy convection likely to encompass the eastern Dakotas through
parts of the Upper Midwest. A strengthening upper jet over Canada
coupled with shortwave progression from the southwest and budding
LLJ over the Plains/Midwest will lead to a robust axis of
convection running west to east along a bisecting warm front
approach from the south with another cold front slowly migrating
southeast out Canada. As the flow begins more strongly veered
within the boundary layer, the approach of the front and shortwave
trough will lead to the mean flow becoming more parallel to the
frontal boundary leading to more uni-directional mean layer winds
and back-building prospects as Corfidi Upshear forecast shifts
sharply out of the north with weaker storm relative motions. This
is indicative on plenty of the numerical guidance in the vicinity
of north-central MN over into northwest WI and the Arrowhead. The
concern in the setup is the exact positioning of where this back-
building/training axis will transpire as the latitudinal
positioning of the front will make all the difference in where the
heaviest precip will occur and maintain over the back half of the
forecast period. Consensus is still riddled with uncertainty on the
specifics, but the probability fields do note the higher potential
being located along and north of I-94 across ND and western MN.
Greatest threat for significant training seems to be building on a
line from Fargo-Duluth and eventually towards Marquette (More on
that area in the D3 discussion below). 

QPF maxima between 4-6" with perhaps a few spots higher when
assessing the different deterministic seems to be the signal as of
now, but we are still only touching the surface of the CAMs.
Considering the environmental parameters (PWATs, instability,
kinematic forcing), the threat is likely well-within the SLGT risk
category with prospects for heavier QPF output as we move closer.
In any case, the SLGT from previous forecast was relatively
maintained with some adjustments on the southern flank of the risk
to note a little more uncertainty in those areas. It's an evolving
setup that could see some shifts in the higher risk area with even
potential for a localized upgrade if consensus on the heaviest
precip axis builds. 

...Southeast...

Elevated PWATs and instability across the Southeastern CONUS will
maintain a posture of widely scattered thunderstorms capable of
locally enhanced rainfall rates between 2-4"/hr that could spur
flash flood prospects through the course of Tuesday. A weak surface
reflection along the SC coast with a weak quasi-stationary front
aligned west to east across the Southeast will lead to enhanced
regional convergence that could allow for slow-moving heavy
thunderstorms to train over any area in proxy to these features for
a few hrs. These are the types of setups that can provide a sneaky
3-6" maxima in any given location, especially near the low pressure
center along the coastal plain. Surface trough extending off the
southern flank of the low will likely bisect southeast GA down
through northern FL with guidance consistently pinning a more
defined heavy precip axis within the confines of this area. FFG's
remain very high across that specific area, so the threat for
widespread flash flooding is very low, especially when considering
the probabilities for >5" are still running <20%, a signal
necessary for more appreciable impacts to occur in these zones. In
any case, some of the output from the CAMs is robust locally, so
the threat still falls within the MRGL risk category. The previous
MRGL risk was generally maintained to reflect the persistent
signal, albeit modest at best.

...Southwest...

Another period of monsoonal type convection will enhance localized
flash flood prospects across eastern AZ and much of NM/CO.
Persistent moisture advection along the western flank of a ridge
positioned across the Mississippi Valley will be the driver for the
threat as scattered showers and thunderstorms will litter the
Southwestern CONUS by Tuesday afternoon, carrying through the
evening hrs. Any area within the confines of the above regions will
have a threat for impacts due to convective cores likely producing
rates >1"/hr with upwards of 2"/hr in the strongest cells. Areal
QPF average is generally between 0.25-0.75", but neighborhood probabilities
for >1" over eastern AZ into NM/CO are well above 70% with >2"
probs running between 40-70% over the more terrain favored areas in
both locations. This is more than sufficient for a broad MRGL risk
encompassing these areas with a possibility of a targeted upgrade
if the heavier QPF signals grow within the CAMs in the coming 24 hrs.

Kleebauer


Day 3
Valid 12Z Wed Jul 23 2025 - 12Z Thu Jul 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE ARROWHEAD
OF MINNESOTA, NORTHERN WISCONSIN, AND THE WESTERN U.P. OF MICHIGAN...

...Upper Midwest...

The progression of convection from the prior D2 will bleed over
into the front half of D3 with the cold front slowly migrating
eastward allowing some advancement of the organized convective
pattern to spill over into the Arrowhead of MN and adjacent
northern WI and western U.P. There's a better consensus on this
occurring given the aligning mass fields from relevant
deterministic, as well as an agreement on the pattern progression 
as the surface low over the northern plains finally lifts northeast
along the front and clears into the northern lakes by Wednesday 
afternoon. The cold front will still be slowly pushing eastward 
through the second half of the period with guidance indicating 
another wave of low pressure potentially enhancing the convective 
pattern across the Upper Midwest into the northern Great Lakes. 
There's a growing consensus on overlap of the two convective 
periods to occur over the far northern tier surrounding Lake 
Superior with multi-round QPF forecasts indicating a regional max 
positioned over the areas referenced above. A SLGT risk was added 
across those respective zones due to confidence in the front end of
the forecast period, but maintained a broad MRGL surrounding with 
extension back west where the second round is forecast. There's 
still some time to delve into the final details on potential 
upgrades across parts of the Plains and Upper Mississippi Valley, 
so stay tuned for updates in future forecast packages.

...Southeast...

A slowly westward migrating upper trough off the Southeast coast
and attendant surface low over the northern Gulf will lead to
locally heavy rainfall prospects from the central Gulf coast over 
into Florida. The signal for rainfall exceeding 3" can be found in 
various deterministic leading to a threat for at least urbanized 
centers due to higher run off capabilities. The overall pattern 
remains very wet with the greatest instability confined to the 
immediate Gulf coast with a secondary maxima over inland central 
FL. A MRGL risk remains positioned over the above zones given the 
threat with the greatest potential for any upgrades likely over the
immediate central Gulf coast. 

Kleebauer
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