Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Sat Jun 28 2025

Day 1
Valid 12Z Sat Jun 28 2025 - 12Z Sun Jun 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE PLAINS INTO THE MID ATLANTIC/NORTHEAST US...

...Northern Plains and Upper Midwest...

Showers and thunderstorms capable of producing locally heavy
rainfall rates and heavy rainfall totals have the potential to
produce flash flooding as the next upper shortwave trough
approaches. Aided by a 90kt upper level jet streak on the lee
side...the upper trough will generate a compact area of fairly
robust, transient deep-layer forcing over the outlook area later
today and tonight. 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 within the unstable airmass will be capable of producing
rainfall rates in excess 1.5 inches 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. The storm/mesoscale nature of the threat
leads to uncertainty of a more focused corridor of higher risk, but
a Slight Risk may still be necessary...particularly over the Upper
Mississippi Valley...if trends remain consistent.

...Mississippi Valley to the Mid Atlantic/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 inches and as
weak mid-level shortwave energy aids convective development in a
high CAPE/weak flow environment over portions of the Mid-
Mississippi Valley into the upper Ohio Valley. Farther north,
maintained the Marginal Risk to account for the possibility that
some of the convective activity across southeastern Canada north
of the warm front clips portions of northern New England. While
guidance indicates the potential for 1-2" of rainfall totals across
the region, the less robust convection on the northern side of the
front should keep any flooding issues isolated.

...Southeast to adjacent southern Plains...

Scattered pulse thunderstorms are expected across a broad warm
sector as seasonable instability develops with daytime heating from
the Southeast and into the adjacent southern Plains. High
precipitable water values (at or above 2 inches, some 2 standard
deviations above the climatological mean for this time of year)
will once again lead to highly efficient rain rates of 1-2" per
hour, possibly as high as 3" per hour, which is more than enough to
lead to isolated flash flooding concerns despite the generally
limited thunderstorm duration. With a signal that has persisted
several runs...introduced a Marginal risk area over parts of the
Florida peninsula for late day convection that fires along a weak
convergence boundary.

...New Mexico...

Yet another day of thunderstorms is expected across portions of
southern New Mexico and west Texas with locally heavy rainfall
(1-2") possible. QPF trends (coverage, intensity) are more isolated
compared to day 1 with the moist south to southeast low-level
upslope flow likely resulting in more localized areas of heavier
rainfall focused across the Sacramento and Guadalupe Mtns south
through the Trans-Pecos. The flash flood potential is expected to
remain isolated.

Bann/Putnam

Day 2
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 from the western Great Lakes south
through the Mississippi Valley and west into the central/southern
Plains and southern Rockies. Showers and thunderstorms are expected
both along and well-ahead of a cold front and trailing surface
trough/dryline as an upper-level trough approaches from the west.
Mechanisms to help focus convection becomes less defined ahead of
the front but deterministic guidance indicates widely scattered
rainfall totals of 1-3" are possible 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.

Waves propagating along the front may help to focus/organize
convection and lead to a more concentrated threat...and remained
supported by localized maxima in the ensemble means/probabilities
in the central Plains/Missouri Valley to the Upper Mississippi
Valley region...confidence remained low with respect to the exact
placement. Bann/Putnam

Bann

Day 3
Valid 12Z Mon Jun 30 2025 - 12Z Tue Jul 01 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE WESTERN PLAINS EASTWARD INTO THE MID ATLANTIC...

Similar to Sunday...convection is expected to develop within a region
of decent CAPE and precipitable water values in excess of 2
standard deviations above climatology. Except for some mid-level
westerly flow around the Great Lakes to provide some shear
there...the flow farther south should be fairly meager (but offset
by steeper low-level lapse rates). This sets up the potential for
some local rainfall rates in excess of 1 inch per hour that results
in excessive rainfall from the Western High Plains
east/northeastward into the Ohio Valley and parts of the Mid-
Atlantic region on Monday and Monday night. A weakening surface
boundary will help focus some of the threat for heavier rainfall
but its placement is quite uncertain. Without much forcing or
confidence in placement of a boundary to focus activity...placement
of any heavy rainfall is low confidence.

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