FOUS30 KWBC 270829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Fri Jun 27 2025

Day 1
Valid 12Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL APPALACHIANS AND NEIGHBORING MID ATLANTIC...

...Northern NY-New England...

The suite of 00Z operational models and ensemble runs continued a 
trend started during the day on Thursday of shifting the focus for 
heavy rainfall to remain north of the international border. Even 
though there are some variances on the possible MCS path which 
could still result in an MCS clipping the northern portion of New
York and New England...it should fall in a region where Flash Flood
Guidance is higher than adjacent areas so the Slight Risk was
removed and the Marginal Risk area was removed from the upper
Hudson Valley and southward. 

At the same time...introduced a Slight risk area over portions of
the central Appalachians where model signals have been growing for
enhanced rainfall amounts near the terrain. With a westward
propagating cold front encountering the terrain... the higher
amounts suggested by the latest HRRR runs seems reasonable and was
placed near the axis of heaviest rainfall from the WPC
deterministic QPF.

...Northern Plains...

A quick moving shortwave across the northern and central tier of 
the CONUS will lead to scattered thunderstorm activity capable of 
locally heavy rainfall. Prospects for flash flooding seem to be 
limited given the progressive nature of the shortwave trough which 
should help focus the convection. A quick 1-3+" is likely anywhere 
over parts of the eastern Dakotas and across central Minnesota. 
This threat remained within the lower end of the MRGL risk 
threshold and will be monitored closely.

...West Texas into New Mexico...

Continued threat of widely scattered thunderstorms across far West
Texas into New Mexico again over an area that will have seen 
several days of heavy convective impacts with compromised Flash 
Flood Guidance. Local 1- to 2-inch amounts are possible in the 
period with the highest threat likely over the Sacramento's down 
through the Guadalupe Mountains and adjacent valleys. A Marginal 
risk was maintained to cover for the threat.

Bann


Day 2
Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF THE NORTHERN PLAINS AND UPPER MIDWEST, THE NORTHEAST, AND SOUTH-
CENTRAL NEW MEXICO...

...Northern Plains and Upper Midwest...

Next approaching upper shortwave trough, with a 90kt upper level 
jet streak on the lee side, will generate a compact area of fairly 
robust, transient deep-layer forcing over the outlook area mainly 
Saturday night. later in the period (especially Sat night). MUCAPEs
are expected to soar within the warm sector prior to the surface 
cold frontal passage. Given precipitable water values getting near 
1.75 inches...storms which form the unstable airmass will be 
capable of producing rainfall rates in excess of 1 inch per hour 
and areal average rainfall amounts of 1 to 3 inches...especially 
once low- level inflow accelerates to between 30 kts and 40kts at 
850 mb ahead of the approaching front.

...Northeast...

There continues to be an increasing concern for heavy to
potentially excessive rainfall to develop across western 
Pennsylvania and surrounding areas as the frontal boundary sags 
southward and taps into the pooled PW values of 1.5-2". The latest 
model guidance are showing local maximums upwards of 2 inches 
possible and the ERO first guess supports expanding the Marginal 
Risk from eastern Pennsylvania further west into eastern Ohio, West
Virginia and western Maryland.

...New Mexico...

Maintained a targeted Marginal Risk area over/near the Sacramento 
Mtns, particularly in vicinity of burn scars. QPF trends 
(coverage, intensity) are similar to Day 1, with the moist south to
southeast low-level upslope flow likely resulting in a 
concentrated area of heavier rainfall across the Sacramento Mtns 
and eastern foothills. The flash flood potential is expected to 
remain isolated/localized.

Bann


Day 3
Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING OVER
PORTIONS OF THE CENTRAL UNITED STATES...

There is a Marginal Risk of excessive rainfall over portions of the
central United States between the western Great Lakes and the
Southern Rockies. Any showers or thunderstorms which form along or
ahead of the front may be able to produce rainfall rates high
enough to result in flash flooding. Away from the upper
trough...mechanisms to help focus convection becomes less defined 
in an atmosphere characterized by precipitable water values in 
excess of 1.5 inches over all but the plains near the Central and 
Southern Rockies to in excess of 2 inches east of the Mississippi. 
Ensemble guidance depicted isolated to widely scattered rainfall 
amounts of 1 to 3 inches but little coherence in placement between 
the ensemble runs. Opted to highlight a broad but generally 
unfocused Marginal risk area .

Bann

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