554
FOUS30 KWBC 061944
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
344 PM EDT Fri Jun 6 2025

Day 1
Valid 16Z Fri Jun 06 2025 - 12Z Sat Jun 07 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS, THE LOWER OHIO, LOWER TENNESSEE AND MIDDLE
MISSISSIPPI VALLEYS AND NEW ENGLAND...

16Z Update...
Prior discussion remains valid outside of a few changes based on
morning guidance. Overall, a stationary boundary stretching over
2000 miles from the Northeast to the Southwest will provide a focus
for numerous convective complexes of varying size and magnitude.
Widely scattered instances of flash flooding can be expected with
the potential for locally considerable impacts.

A SLGT risk was added for the LUB CWA in western TX along with the
expanded MRGL along the dry line to the TX Big Bend. Similar setup
to yesterday is expected to compound the potential for isolated to
scattered flash flooding, particularly if developing HP supercells
this afternoon impact urban regions with 2-5" totals.

Additionally, the SLGT risk across New England was expanded a bit
based on current radar and satellite trends showing a shortwave
passing over the Interior Northeast that will help spark
thunderstorm activity along an east- west oriented stationary front
extending through southern New England into central PA. 12Z HREF
and most 12Z CAMs are particularly impressive with the high-end
potential over NH given slow-moving convection initiating off the
higher elevations. 12Z HREF probabilities for greater than 5" are
as high as 25% across parts of NH.

For the Ohio and Tennessee valleys, the SLGT risk was expanded
eastward into eastern KY based on latest radar trends as a potent
MCV over southern MO riding along the stationary front draped over
the Ohio Valley. See MPD 308 for more information. 12Z HREF was not
overly impressive in magnitude across this region for 2"+ amounts,
but coverage is expected to widespread enough to lead to scattered
instances of flash flooding.

Snell


Previous Discussion...

...South-Central Plains.....
There is a strong model signal for another round of organized
convection late Friday afternoon into Friday night/early hours of
Saturday across the south-central plains as additional shortwave
energy is forecast to drop east southeastward from the Central
Rockies into the Central to Southern Plains Friday into Friday
night/early Saturday. The low level flow is expected to again
strengthen into the west to east oriented frontal zone across the
Southern Plains, supporting potential for another round of
organized convection in the vicinity of this front. PW values
along this front will remain above average...2+ standard deviations
above the mean, supporting heavy precip potential. There is fairly
good model consensus for an axis of heavy rains along this front
from far southeast CO/far southwest KS, across much of OK into the
OK/KS/MO/AR border region. The slight risk was drawn to fit the
axis of the highest HREF neighborhood probabilities for 2"+ amounts
and the HREF EAS axis of highest probabilities for 1"+ amounts. The
next round of organized convection will likely track along the same
areas that are currently receiving heavy rainfall late Thursday
evening into early Friday for northern OK, compounding the
potential flash flooding concerns and leading to the potential for
more widespread and considerable impacts overnight.

...Mid Mississippi Valley, Lower Ohio Valley, Lower Tennessee
Valley...
The lead area of shortwave energy initiating current early morning
convection across the Southern Plains will be pushing toward the
Mid Mississippi Valley, Lower Ohio and Lower Tennessee Valleys
Friday afternoon/evening. Similar to areas upstream along the west
to east oriented frontal zone that extends into the Mid MS, Lower
OH,Lower TN Valley, PW values will be above average, 2+ standard
deviations above the mean. Convection likely to enhance Friday
afternoon/evening ahead of these height falls in the much above
average PW axis, supporting heavy rain potential and localized
flooding issues. A slight risk area was added from the previous
issuance, aligned with where the axis of the highest HREF
neighborhood probabilities for 2"+ amounts and the HREF EAS axis of
highest probabilities for 1"+ amounts are forecast.

...Southern Great Basin into the Central to Southern Rockies...
Not a lot of changes expected to the large scale flow across the
southern Great Basin into the Central Rockies. PW values forecast
to remain above average with additional shortwave energy moving
across the region in the west south west flow aloft. This should
support another day of widespread scattered convection and
localized heavy rain and isolated runoff issues. No significant
changes made to the previous marginal risk area across this region.

...East-central New York into Central New England...
A slight risk area was added for portions of east-central New York
State into central New England from central to southern New
Hampshire, across southeast Vermont, western Massachusetts into
east central NY state. There is good agreement in the last hi res
guidance for enhancing convection in the 1800 UTC Friday to 0000
UTC Saturday period in the axis of above average PW values along
the slow moving frontal boundary draped across this area. The
slight risk was drawn to fit where the axis of high HREF
neighborhood probabilities are for 2 & 3"+ totals. This corresponds
also to where the HREF hourly probabilities for 1"+ totals are
high in the 1800 UTC Friday to 0000 UTC Saturday period.

Oravec


Day 2
Valid 12Z Sat Jun 07 2025 - 12Z Sun Jun 08 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE LOWER
ARKANSAS VALLEY, LOWER MISSISSIPPI VALLEY INTO THE LOWER TENNESSEE
VALLEY...

...Eastern Oklahoma and Northeast Texas to Central/Northern
Alabama...
The second round of height falls moving into the Central
to Southern Plains day 1 will continue to push east southeast
toward the Mid to Lower MS Valley, OH and TN Valleys during day 2.
Upper difluence is forecast to be well defined Saturday into
Saturday night/early Sunday in an axis of above average PW values
that will remain along the west to east oriented frontal boundary
across these areas. This should support potential for another round
of organized convection along this front as well as near a well-
defined mid-level circulation passing to the north into the Ohio
Valley. There is some spread with the qpf axes, but consensus that
heavy amounts are possible. The inherited Slight Risk area was
shifted a bit south and removed from most of TN given southern
trends with the early morning MCS and related redevelopment along
the associated lingering outflow boundary through the early evening
into northeast TX.

...Middle Mississippi and Ohio Valleys...
Mid-level wave ejecting out of the central Plains Saturday morning
will continue to push eastward across the Ohio Valley. This
feature will aid in increased moisture return and shear to provide
for scattered to numerous showers and thunderstorms. The inherited
Marginal Risk was expanded northward to capture this trend of more
precipitation attached to the mid-level low. A Slight Risk may be
necessary across the Ohio Valley from southern IL to northern KY
and southern OH, but this area is conditional on whether enough
instability can build ahead of the mid-level shortwave pushing
eastward. Should guidance come into better agreement this upgrade
may be needed, with latest HREF probs for at least 2"/6-hr up to
40%. Antecedent conditions are also rather wet, so that will need
to be considered as well with current convection for the next
overnight update.

...Northeast PA through New England...
Another round of convection possible early day 2 along the frontal
boundary pushing through the northeast as a sharpening northern
stream trof pushes eastward across northern NY into New England.
The HREF neighborhood probabilities for the 12 hour period from
1200 UTC Saturday to 0000 UTC Sunday, are high along this front for
1 and 2"+ amounts. The previous marginal risk area was extended
farther west into northeast PA to cover these higher 12 hour
probabilities. There may need to be an upgrade to the risk level in
future issuances depending upon where the heavy rains occur during
day 1.

Snell/Oravec


Day 3
Valid 12Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS NORTHERN
TEXAS AND SOUTHERN OKLAHOMA...

...Southern Plains to the Southeast...
Additional shortwave energy likely to push east southeastward late
Sunday afternoon/evening from the lee of the Central to Southern
Rockies into the Southern Plains under the influence of a much
stronger upper level low centered over the north-central United
States. This will again re- strengthen the low level flow into the
west to east oriented front forecast to remain across the Southern
Plains, supporting another round of organized convection along the
front. There is fairly good agreement on the day 3 qpf axes in the
models. Resulting in good continuity with the slight risk area
with only a subtle expansion and south shift where widespread rainfall
amounts of 2-4" are expected and higher amounts possible.
Additional thunderstorm activity is expected from early morning
convection and afternoon redevelopment along the frontal boundary
through the Southeast, with mostly isolated flash flooding
concerns.

...Central Appalachians and Upper Ohio Valley...

Meanwhile, the mid-level wave progressing across the Ohio Valley on
day 2 will continue into the central Appalachians and northern
Mid-Atlantic while interacting with a lingering frontal boundary.
This will produce additional areas of scattered areas of convection
and the potential for isolated instances of flash flooding within
typically sensitive terrain. There remains higher than average
uncertainty regarding the speed of this system, which could impact
the eventual flash flood risk area.


Snell/Oravec


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