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FOUS30 KWBC 111545
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1145 AM EDT Mon Aug 11 2025

Day 1
Valid 16Z Mon Aug 11 2025 - 12Z Tue Aug 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS, COASTAL CAROLINAS INTO GEORGIA AND ACROSS THE
FLORIDA PANHANDLE...

...16z Update...

Previous forecast remains largely on track based on observational
trends and the latest 12z hi-res suite across the relevant regions.
Some modest expansion of the SLGTs (westward into more of the TX
Panhandle, as well as southward from coastal SC into coastal GA)
occurred (12z HREF neighborhood probs for 5" exceedance of 10%+),
as well as a more substantial expansion of surrounding MRGL areas
(to include more of the southern and central Appalachians with much
higher PWATs and instability compared to 24-hr ago, as well as
into portions of eastern KS and southwest NE in association with
convective redevelopment in the vicinity of an MCV from overnight).

Churchill


...Previous Discussion...

...Southern Plains...
The active early morning convection currently across portions of
the Southern and Central Plains will likely weaken prior to or
shortly after 1200 UTC Monday. The latest hi res model consensus is
for the next round of convection to then form farther south along
the surface frontal boundary stretching from the Southern High
Plains, northeastward into the Lower MO Valley. No major changes
made to the previous slight risk area, with the current version
fitting well where both the HREF mean and RRFS mean neighborhood
probabilities for 1 and 2"+ amounts are high. PW values will remain
high, 1.5 to 2"+ in the slight risk area. This combined with
favorable upper difluence on the southeast side of the slow moving
mid to upper level trof moving across the Southern Plains, will
support potential for additional heavy precipitation totals. A
period of slow moving/training cells parallel to the frontal
boundary, primarily in the 0000 to 1200 UTC Tuesday period will
support localized hourly rainfall rates of 1"+.

No changes made to the marginal risk area extending farther to the
northeast into the Mid Mississippi Valley and Lower Lakes region.
The HREF and RRFS mean neighborhood probabilities are not as high
for 1 and 2"+ amounts as over the Southern Plains. Localized heavy
rainfall amounts along this portion of the front, are expected to
be to the south of where the heaviest rainfall fell over the past
24 hours from northeast IA, far northwest IL and southern WI. For
these reasons, the threat level was maintained as marginal.

...Northeastern Gulf Coast...
An axis of tropical PW values, 2 to 2.25"+, will push
northwestward in association with mid level shortwave energy moving
across the northeastern Gulf. Active showers likely in this high
PW axis along the immediate central to northeastern Gulf coastal
regions. HREF and RRFS mean neighborhood probabilities are high for
for 1, 2 and 3"+ totals from the Florida Panhandle, west across
far southern AL, far southern MS, southern LA into coastal
northeast TX. A slight risk was maintained across the FL Panhandle
region. The marginal risk was extended westward to cover the high
HREF and RRFS mean neighborhood probabilities across far southern
AL, far southern MS, far southern LA into coastal northeast TX.
There is consensus for potentially two periods of potentially
.50-1"+ hourly rainfall amounts during the day 1 period. The first
early this morning, extending into the post 12Z Monday period,
followed by another uptick in coastal precip intensities in the
early hours of Tuesday, 0600-1200 UTC.

...Coastal South and North Carolina...
The anomalous PW axis moving northwest into the immediate Gulf
Coast day 1 will also remain in place farther to the northeast
from GA into SC and NC. Only some small changes made to the
previous slight risk areas along the SC and NC coasts, extending
the slight risk approximately 50 miles farther northeast along the
NC coast to cover the latest model qpf and higher HREF/RRFS
probabilities. Active showers likely in this anomalous PW axis as
onshore south southeasterly flow persists day 1. There will be the
likelihood of training of precip areas in the south southeasterly
flow, supporting localized hourly rainfall totals of 1-2"+. The
marginal risk area over west central NC was extended approximately
50-100 miles to the north to cover the latest model qpf.

Oravec


Day 2
Valid 12Z Tue Aug 12 2025 - 12Z Wed Aug 13 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
LAKES, SOUTHWESTWARD INTO THE MIDDLE MISSISSIPPI VALLEY AND INTO
THE SOUTHERN PLAINS, FROM THE CENTRAL GULF COAST INTO THE
CAROLINAS AND ACROSS PORTIONS OF THE SOUTHWEST...

...Lower Lakes into the Mid MS Valley and Southern Plains...
An axis of high PW values, 1.5-1.75"+ will continue along and ahead
of the elongated frontal zone stretching from the Lower Lakes,
southwestward into the Mid MS Valley and into the Southern Plains.
Scattered convection likely in this high PW axis, supporting
locally heavy precip totals. The previous marginal risk area was
extended farther southwestward from southern MO, across northwest
AR, much of OK and into northern TX to cover model qpf spread. Also
expanded the previous marginal risk area farther northwestward
into eastern WI and the northern portion of the L.P. of MI to cover
the model qpf spread for potentially locally heavy rainfall totals
along the northern portion of the frontal zone across these areas.


...Central Gulf Coast into the Carolinas...
The axis of high PW values stretching from the Central Gulf Coast
into the Carolinas on day 1 will persist across these regions day
2. Shortwave energy embedded in this high PW axis will continue to
support potential for additional heavy rains day 2. The previous
marginal risk area was extended east northeastward from northern
GA/Upstate of SC/far western NC to cover much of the remainder of
NC and SC where several models show heavy rain potential.

...Southwest...
No changes made to the previous marginal risk area from southeast
AZ into much of NM. Weak shortwaves progged to rotate around the
mid to upper level ridge building eastward into the Great Basin day
2, enhancing large scale uvvs in an axis of seasonable PW values.
Scattered convection across this area will support potential for
localized heavy rainfall amounts and isolated runoff issues,
especially across more vulnerable terrain features or burn scars.

Oravec


Day 3
Valid 12Z Wed Aug 13 2025 - 12Z Thu Aug 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY INTO THE TENNESSEE AND OHIO VALLEY AND EASTERN
LAKES, ACROSS COASTAL SOUTH CAROLINA AND COASTAL NORTH CAROLINA,
PORTIONS OF THE NORTHERN PLAINS AND OVER THE SOUTHWEST...


Similar to the day 2 period, an axis of high PW values will
continue to stretch from the Central Gulf coast, east northeastward
into the Southeast and Southern Mid Atlantic. Widespread scattered
convection likely in this anomalous PW axis, values 1.5-2 standard
deviations above the mean. Mid to upper level dynamics will have
weakened by day 3, with less defined areas of upper diffluence to
accentuate lift in this high PW axis. Still, model consensus is for
continued potential for continued locally heavy rains across these
areas. A marginal risk was added for the upper coast of SC and the
lower coast of NC where models do show potential for additional
locally heavy rains day 3.

...Lower Lakes/Northeast into the OH/TN Valley, Central to
Southern Appalachians...
An axis of high PW values, 1.5-1.75"+ also likely to continue
along the elongated frontal zone pushing eastward through the Lower
Lakes into NY State and northern New England and stretching
southwestward into the OH/TN Valley regions and Central to Southern
Appalachians. Widespread scattered convection likely along this
front in this high PW axis, supporting locally heavy rains and
isolated runoff issues. No changes made to the previous marginal
risk area along and ahead of this front.

...Southwest...
No significant changes to the overall flow pattern for the
Southwest day 3. Additional weak vorts rotating around the Great
Basin/Southwest mid to upper high will support another round of
scattered convection. Low confidence on any qpf details, but
potential will continue for localized heavy rains and isolated
runoff issues, especially across more vulnerable terrain features or burn scars.

...Northern Plains...
The low level southerly flow expected to strengthen after 0000 UTC
Thursday across the Northern Plains ahead of a surface front
emerging into the Northern Plains. An area of organized convection
possible ahead of this front, with locally heavy precip totals
possible. There is a lot of model spread with qpf details at the
moment, leading to low confidence. The previous marginal risk area
was decreased in size to better fit the overlap of potentially
heavy rains with the lower FFG values.

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