Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1142 AM EDT Sun Jun 15 2025

Day 1
Valid 16Z Sun Jun 15 2025 - 12Z Mon Jun 16 2025

...A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA...

...Mid-Atlantic and Central Appalachians...

16Z Update: The previous MDT risk was maintained with some
expansion to the northwest to reflect the latest prob fields
highlighting a greater threat north of Richmond as convection fires
and slides down the instability gradient aligned with the front.
Biggest shift was the expansion of the SLGT a bit further north and
northwest into Southeast OH and more of Western PA as area 1/3/6 hr
FFG indices are incredibly low given the saturate grounds lingering
from yesterdays convective impacts. Environment in place is
conducive for locally enhanced rainfall rates with the stronger
cores more apt to produce intra-hour rates closer to 3"/hr with an
average 1-2"/hr intensity in any thunderstorm development. The area
over Northern and Eastern WV is also under a greater threat for
flash flooding today due to similar characteristics noted to the
north. Complexity of the terrain adds more opportunity for locally
significant flash flood concerns, something that has historical
precedence in these areas encompassing the Central Appalachian's.
In all, the setup remains on the higher end of the SLGT spectrum
for much of VA into WV and Southwest PA with a targeted MDT down
over Southern VA and the Tidewater due to the more robust PWAT
and instability signatures within the confines of quasi-stationary
front creating a greater threat for training convection.

Kleebauer

..Previous Discussion..

A back door cold front will continue to slow down its forward
progress and idle across the Mid-Atlantic region through Father's
Day. Moist southwesterly flow will intersect this boundary and
result in enhanced moisture convergence and lift. A combination of
ample instability on the order of 1000-2000 J/kg of mixed layer
CAPE, PWs nearing 2 inches, and a strong frontal boundary will set
the stage for additional heavy rain over grounds that are becoming
much more saturated leading up to this. There are two main areas of
increased concern, with the first being over eastern West Virginia
where HREF probabilities of flash flood guidance exceedance are
elevated due to antecedent conditions and the prospects of 1-2
inches of additional rain on Sunday. Although this area still
remains in a Slight Risk, there is the potential that an upgrade to
Moderate Risk may be needed once the event starts to materialize
midday Sunday, so this will continue to be closely monitored.

The other area of concern is across the Tidewater region of
southeast Virginia into adjacent portions of northeast North
Carolina. The 00Z CAM guidance strongly supports swaths of enhanced
QPF from just south of Richmond to the northern Outer Banks, and
rainfall totals on the order of 2-3 inches, and locally higher, are
expected. This would be falling on top of grounds that already had
1-3 inches on Saturday near the U.S. Highway 460 corridor into
Southside Hampton Roads, so that is an aggravating factor. All of
this combined with higher HREF flash flood guidance probs resulted
in areas south of the James River and north of the Albemarle Sound
to now be in a Moderate Risk for this time period.

Hamrick


...Mid-South to the ArkLaTex...

16Z Update: MCS currently migrating south across the Red River will
continue propagating towards Southeast TX before fizzling out on
approach once south of I-45. Current indications are a combination
of differential heating causing destabilization over Southeast TX
will initiate another round of pulse convection with the remnant
cold pool of the MCS eventually interacting with storms already in
the area. Some minor convergence signatures are popping up within
CAMs, but the threat seems to be relatively minor compared to
previous setups as the stable component behind the complex provides
a cap on the activity pretty quickly once the interaction occurs.
HREF probs are generally modest for >3" potential, but fall off a
cliff to near 0% for >5", so the realistic maximum is somewhere
between 3-5" with an areal average closer to 1-2" where convection
does occur. The greater convergence signature is up closer to the
Northwest Ozarks where satellite combos and even regional radar
composite depict a broad MCV slowly drifting eastward with the mean
flow leading to a small band of light/moderate rainfall in the
northern quadrant of the circulation.

The area to the southeast is the most prone to convective
initiation and relatively impacts due to the proxy and persistent
advection of moisture within the southeast and eastern flank of the
meso-low. Visible satellite indicates a broad area of clearing
which will likely enhance regional instability prospects given the
"green light" for diurnal destabilization pattern. CAMs are in
agreement on another round of heavy convection over the areas
outlined within the zone of clearing leading to elevated
neighborhood probs for >3" (50-70%) across Central and Northern AR
into Southeast MO. The former area has been hit multiple times over
the past 24-48 hrs leading to some priming of the soils so the
threat for flash flooding is a bit higher compared to Southeast MO.
Will need to monitor that region closely overnight to see how the
convective pattern evolves, but the previous SLGT risk inherited
was sufficient to warrant continuity as the setup has maintained
similar posture within the 12z CAMs suite and ensemble. The threat
over TX is still well within the MRGL threshold and given the cap
on potential, the risk was not upgraded as the threat remains more
localized with greatest potential in urbanized zones. Will monitor
the MCS evolution closely as any changes in the near term could
allow for a targeted upgrade, namely in the area along I-35.

Kleebauer


...Upper Midwest...

16Z Update: The signal for the SLGT is favorable on the threat as
most CAMs remain aggressive for the evening complex anticipated to
slide down the eastern flank of the theta_E ridge positioned over
the Plains. HREF EAS and neighborhood prob fields still highlight
that area of far Southeast SD, Northwest IA, and Southwest MN this
evening with the greatest chance for locally 2-4" of rainfall.
Considering the antecedent soil moisture being elevated after this
mornings convective impacts, the foundation was laid for a targeted
opportunity to see some localized flash flood prospects. This
allowed for little to no change in the previous forecast as the
threat is still on track.

Kleebauer

..Previous Discussion..

The expected convective complex over the Dakotas and moving into
Iowa will likely be more on the progressive side compared to the
MCS farther south across Arkansas. However, some of the heavier
rain that is expected will likely happen over more saturated soils
and therefore a higher chance of localized impacts. The 00Z CAM
guidance suite has trended wetter, especially the 3km NAM, and the
global guidance to include the GFS and the CMC also have a more
concentrated QPF signal. Therefore, northwestern Iowa and portions
of adjacent states are now in a Slight Risk area for this time
period.

Hamrick


Day 2
Valid 12Z Mon Jun 16 2025 - 12Z Tue Jun 17 2025

...A MARGINAL RISK OF EXCESSIVE RAINFALL IS VALID FOR PORTIONS OF
THE UPPER MIDWEST, MID-SOUTH, AND THE MID-ATLANTIC...

...Mid-Atlantic region...

Overall, an improvement compared to what is expected over the
weekend, but there should still be enough moisture in the general
vicinity of a stalled stationary boundary over southern Virginia
and North Carolina to produce scattered storms with heavy rainfall.
There is a greater signal in the 00Z guidance for heavier QPF
across central and southern North Carolina, but it does not appear
to overlap much with the Day 1 QPF, so this will tend to mitigate
the flooding potential. Although the magnitude of rainfall
expected on Monday is not impressive, the very saturated ground by
this time across West Virginia and western Virginia will be an
aggravating factor in terms of flooding potential, and therefore a
Marginal Risk area is valid from central West Virginia to the Outer
Banks of North Carolina.

...Mid-South...

The latest model guidance is honing in on a potential MCS that
could develop across portions of eastern Arkansas into western
Tennessee on Monday, and perhaps extending into portions of
southern Missouri and western Kentucky where the potential exists
for 1 to locally 2 inches of rainfall. A Marginal Risk area is
valid here since much of this rain would likely happen over a two
hour time period.

...Dakotas to the western Great Lakes...

Consensus for locally heavy rainfall across portions of the
Northern tier of the CONUS remains favorable across a broad area
extending through the Dakotas, Nebraska, and the Upper Midwest on
Monday. It remains the case that some of the heavier rainfall is
expected over the Sandhills of Nebraska where flash flood guidance
is high, and therefore not rising to the level needed for a Marginal
Risk in that area. Elsewhere, there remains a scattered heavy rain
threat over the northern portions of the Upper Midwest at this
time, and therefore a Marginal Risk remains valid there.

Hamrick


Day 3
Valid 12Z Tue Jun 17 2025 - 12Z Wed Jun 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST STATESâ€

...Midwest states...

A well organized mid-upper level shortwave trough will eject
eastward from the Rockies to the central Plains Tuesday afternoon
into the early hours of Wednesday morning, and this will sustain
the development of a surface low that will develop along a frontal
boundary. Upper level dynamics will be favorable as the region will
be place under the right entrance region of the main upper level
jet, and incoming mid-level positive vorticity advection will
further aid ascent. Precipitable water values in the warm sector of
this surface low are expected to rise into the 1.75 to 2 inch
range and an increasing southwesterly low level jet that will
advect copious moisture into the system.

Model guidance has trended a little to the south over the past few
model cycles, with the greatest consensus for the heaviest QPF
across the southern half of Iowa and over the northern third of
Missouri, and extending to northeast Kansas and west- central
Illinois. Most model solutions have a broad corridor of 1-2 inches
with embedded 3-4 inch maxima within this region, with the majority
of this happening within the 18Z Tuesday to 6Z Wednesday time
period. The heavy rain that fell across portions of the Upper
Midwest is generally north of where this expected rainfall will be,
so grounds will not be saturated in most cases leading up to this
event. The inherited Slight Risk from the previous Day 4 outlook
will be maintained with a southward expansion to it, and a broader
Marginal Risk extending across South Dakota and eastward to include
the greater Chicago metro area.

...Appalachians...

The stationary front that will be lingering across the Mid-Atlantic
will start to slowly move back north as a warm front on Tuesday
with anomalous PW values remaining in place. Scattered to numerous
showers and storms, some of which will likely be slow moving, are
forecast to develop during the afternoon and evening hours, mainly
in the 18Z-00Z time period. Parts of the central Appalachians have
been hammered with multiple heavy rainfall events and this has
served to lower flash flood guidance values, and additional heavy
rainfall in the Day 1 and Day 1 periods will only make the ground
more saturated. Therefore, a Marginal Risk is valid from western
North Carolina to western Pennsylvania.

Hamrick


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