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FOUS30 KWBC 291942
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Sun Jun 29 2025

Day 1
Valid 16Z Sun Jun 29 2025 - 12Z Mon Jun 30 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF THE
CENTRAL PLAINS AND MIDDLE MISSISSIPPI VALLEY...

Late-June weather pattern remains in place 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, a stationary boundary
extending from the Mid-Atlantic to the Great Lakes, as well as
associated with diurnal monsoon activity across the southern
Rockies and adjacent High Plains.

Current radar and satellite imagery shows continued thunderstorm
activity from overnight across the eastern central Plains and into
the Mid-Mississippi Valley, producing mostly isolated flooding
concerns and Flash Flood Warnings ongoing across central MO. With
models showing renewed convection later today and tonight across
western Missouri/eastern Kansas that extends northward into
portions if Iowa...the Slight Risk was maintained. This renewed
convection is forecast to be driven by a sinking cold front and
diving upper trough over the north-central U.S.. 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, southern NE
and southern IA. However, given this event is within 12 hours
there remains rather large uncertainty within CAMs on convective
initiation and some may be picking up on morning convection laying
an outflow boundary farther south and limiting northward
development this evening across NE and southern IA or potentially
delaying it until late tonight. Either way, where heavy rain does
overlap with recently saturated soils, scattered flash flooding is
possible.

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 sensitive
terrain of the central Appalachians, isolated flash flooding is
possible. As always, should these intense and hard to pinpoint
tropical downpours occur over highly urbanized areas, flooding
impacts could become more impactful.

Snell


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

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO AND WESTERN TEXAS...

A Slight Risk was introduced across New Mexico and into western
Texas with today`s update. The driving factor behind the scattered
flash flood threat will be a frontal boundary dropping south into
the southern Plains and southern Rockies. This front will supply
moist easterly flow into the complex terrain of the southern
Rockies and provide greater coverage of thunderstorms by the
afternoon due to diurnal heating, increasing lapse rates and
instability. PWs of 1-1.5" are forecast and will near the 90th
climatological percentile and support rainfall rates of 1-2"/hr.
Additionally, widespread thunderstorm activity is also expected
into the southern High Plains along the associated frontal boundary
within an area of very weak mid-level flow. Storms will likely be
slow-moving across western Texas and eastern New Mexico before
becoming outflow dependent unless a large enough cold pool can
organize a larger thunderstorm complex.

Elsewhere, 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 Plains
east/northeastward into the Ohio Valley and parts of the Mid-
Atlantic region on Monday and Monday night. Some details are coming
into focus, which includes the likelihood of overnight convection
lingering into early Monday morning across parts of the central
Plains and Mid-Mississippi Valley. This activity led to an
expansion of the previous Marginal Risk northward. Meanwhile, an
upper trough lingering across the Southeast will continue to foster
an area of convergence on the southern/southwestern periphery,
which could lead to locally heavy rainfall along the eastern Gulf
Coast and much of the northern Florida Gulf Coast. There is some
potential for extremely heavy rainfall within this tropical airmass
and PWs of 2.25-2.5", but there`s the potential for most rainfall
to occur over the Gulf waters at this time.

Farther north into the Ohio Valley, Appalachians and Northeast, a
weakening surface boundary will help focus some of the threat for
heavier rainfall with its placement remaining 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. The inherited Slight Risk was expanded
somewhat to the southwest in order to capture an area where mean
flow is briefly parallel to eventual line of thunderstorms before
the cold front kicks things eastward Tuesday night.

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. A strong surge of
moisture is expected to push deeper into the Four Corners by
Tuesday in response to tropical moisture pushing northwestward
across Mexico and lifting to the east of a closed low churning near
the California coast. This could lead to greater thunderstorm
coverage across the Southwest/Four Corners on Tuesday and a broader
isolated flash flooding threat.

Snell/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