Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Fri Jun 27 2025

Day 1
Valid 16Z Fri Jun 27 2025 - 12Z Sat Jun 28 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL APPALACHIANS...

...Central Appalachians...

A more focused thunderstorm/heavy rainfall threat is expected
through the central Appalachians today as very moist flow interacts
with the terrain ahead of a 'back-door' cold front passing through
the Mid-Atlantic that will become quasi-stationary throughout the
day. Of particular concern is the prospect suggested by some of the
12Z hi-res guidance (HRRR and HREF) that initial storms over parts
of western Maryland/West Virgina Panhandle/northwestern Virginia
will cluster/organize and move slowly southward along the
instability gradient ahead of the stalling front. Updated 12Z HREF
probabilities are between 40-60% for rainfall of 3"+, with a
focused area of 20-30% of 5"+ across the West Virginia Panhandle.
Efficient rainfall rates of 1-2.5" per hour can be expected given
PWATs upwards of 2" per 12Z PBZ sounding. Much of this region
remains more sensitive to additional rainfall not only due to the
typical terrain impacts but a number of recent heavy rainfall
events keeping FFGs low, with scattered to potentially numerous
instances of flash flooding possible.

...Northern NY-New England...

The suite of 12Z operational models and ensemble runs continues 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.

...Southern Plains into the Mississippi Valley and Southeast...

Another typical Summer day of scattered thunderstorms is expected
broadly from the Southeast through the Mississippi Valley and west
along a surface trough through the southern Plains given seasonable
instability with daytime heating and a passing upper- wave. Pulse-
type thunderstorms will have the ability to produce quick efficient
bursts of heavy rainfall (1-3") and the risk for some mostly
isolated urban flooding, especially where any storms
develop/congeal along residual outflows.

...Northern Plains...

A quick moving shortwave across the northern and central tier of
the CONUS will lead to thunderstorm activity capable of locally
heavy rainfall, especially if convection can grow upscale into a
more organized MCS as indicated by some of the 12Z hi-res model
guidance. However, prospects for flash flooding still seem to be
limited given the progressive nature of the shortwave
trough/possible MCS. A quick 1-3+" is likely anywhere over parts of
the eastern Dakotas and across central Minnesota.

...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.

Putnam/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


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt