411
FOUS30 KWBC 290828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Sun Jun 29 2025

Day 1
Valid 12Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL EXTENDING FROM
PORTIONS OF THE CENTRAL UNITED STATES TO THE CENTRAL GULF COAST AND
MID-ATLANTIC...

Late-June weather pattern remains in place on Sunday with widely
scattered showers/storms and isolated chances for flash flooding
within the warm and humid airmass spanning from the central U.S. to
the Southeast and Mid-Atlantic. Showers and thunderstorms are
expected both along and well- ahead of a cold front sinking
southeastward across the central Plains and Midwest, as well as
associated with diurnal monsoon activity across the southern
Rockies and adjacent High Plains.

As Day 1 begins, late-night convection lingering across parts of
Missouri should be about to fade with the weakening of a low level
jet. With models showing renewed convection later today and tonight
across western Missouri/eastern Kansas that extends northward into
portions if Iowa...did introduce a Slight Risk area to the
outlook where organized convection from overnight approached the
area from the north. Precipitable water values approaching 2" and
near the 90th climatological percentile will provide the
opportunity for intense rainfall rates scattered 2-4" rainfall
totals between parts of KS, MO, and southern IA.

Elsewhere within the warm sector across the Mid-South, Mid-
Atlantic, Southeast, and Southern Rockies/High Plains, typical
summer thunderstorms exhibiting scattered and a pulse mode are
likely. These storms may contain briefly very intense rainfall
rates, but see updrafts collapse quickly and become outflow
dependent. Where convective clusters merge or linger near a
stationary front draped across the Mid-Atlantic and central
Appalachians, isolated flash flooding is possible.

Bann/Snell


Day 2
Valid 12Z Mon Jun 30 2025 - 12Z Tue Jul 01 2025

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

Similar to today...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 Southern Rockies/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 remains quite uncertain.
One area that is still being monitored for a potential upgrade to a
Slight Risk are parts of the Upper Ohio Valley and central
Appalachians (centered over western PA). The synoptic setup with a
stationary/warm front stretching across southern PA and an
approaching cold front from the west should help foster greater
coverage in showers/storms within a moist environment, but storm
motions within a mean column wind of 30kts could limit the flooding
threat even though this area remains sensitive to intense
rainfall. Therefore, a Marginal Risk was maintained to highlight
the threat for isolated flash flooding.

Snell/Bann

Day 3
Valid 12Z Tue Jul 01 2025 - 12Z Wed Jul 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
THE MID ATLANTIC...

The boundary that helps focus some of the threat for heavy to
potentially excessive rainfall on Day 2 will continue to shift
eastward and provide the focus for another round on Day 3.
The flow aloft becomes more supportive over the Northeast US as
divergence aloft increases in response to a digging trough aloft
and low level convergence increases along the boundary. Portions
of the Mid-Atlatic have suppressed Flash Flood Guidance from a
period of above normal rainfall making that area a bit more
susceptible to excessive rainfall...while faster cell motions
should preclude more than isolated instances of flash flooding
across the Northeast US.

Farther south/west along the boundary...convection is expected to
be develop within a region of decent CAPE and precipitable water
values in excess of 2 standard deviations above climatology. With
weaker flow aloft...locally heavy rainfall totals could result in
isolated instances of excessive rainfall.

Bann


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