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FOUS30 KWBC 050824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Wed Feb 5 2025

Day 1
Valid 12Z Wed Feb 05 2025 - 12Z Thu Feb 06 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE OHIO VALLEY...

No significant changes were made to the Marginal Risk area across
the Ohio Valley. Warm advection showers are expected to break out
over Kentucky, that with the infusion of upper level support and
increasing instability, will allow embedded convection to develop
this afternoon and evening. As the moisture plume turns the front
into a warm front over the Tennessee Valley this evening, expect the
addition of upslope into West Virginia to resulting locally
heavier rainfall in the favored areas. Any thunderstorms will be
capable of rainfall rates to 1.5 inches per hour. Soils in this
area remain nearly saturated and rivers are running high from the
rainfall event a few days ago. Thus, the additional rainfall
forecast today and tonight, even though amounts will likely be
lesser, may still cause isolated flash flooding.

Wegman


Day 2
Valid 12Z Thu Feb 06 2025 - 12Z Fri Feb 07 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE OHIO VALLEY AND CALIFORNIA...

...OH Valley...
Another round of locally heavy rain is expected Thursday across
portions of KY, TN, WV and far western VA along and ahead of an
approaching cold front. Showers and embedded thunderstorms will
likely be ongoing at 12z and may periodically continue through the
day/evening near the only slowly southward shifting front. While
nothing significant, CAPE upwards of 500-1000 j/kg still seems
likely along this corridor, which should be enough to support
locally heavy rainfall rates. While soil conditions and
streamflows are returning closer to average after the flooding
several days ago, some of this region is still likely more
sensitive than normal to additional heavy rainfall. The latest WPC
QPF is generally 0.75"-1", with two day totals locally exceeding
1.5". Given the instability forecast, it seems reasonable that we
will see isolated totals over 2". While the 00z GEM Reg and FV3LAM
are probably too high with totals, they both do suggest that if
convective coverage can increase enough then some 2-3" amounts can
not be ruled out. Overall expect this rainfall to pose a localized
flood risk.

...California...
After a one day break another system is forecast to move into CA
on Thursday. This is expected to be a pretty dynamic system, with a
strong mid level shortwave and upper level jet. These dynamics
should support a short duration period of enhanced rainfall
rates...although the quick forward motion of the system will limit
overall rainfall magnitudes. Recent model runs are showing some
uptick in rainfall amounts with this system over northern CA, but
still generally looking at totals in the 1-2" range. Given the
saturated conditions and brief potential for higher rates between
00z and 06z, this may be approaching Slight risk levels. Although
will hold off for now as the short duration of these higher rates
may limit the magnitude/coverage of impacts just enough to keep the
risk at Marginal.

The Marginal risk extends southward into Santa Barbara, Ventura and
Los Angeles counties as well. Less rainfall forecast here, but
there is an uptick in IVT into the terrain Thursday night, and PWs
do increase towards and just over 1". Larger scale forcing
generally shears off to the north, but the combination of
increasing PWs, IVT and upslope flow should be enough to result in
a period of moderate to locally heavy rain. We are beginning to
see a slow uptick in rainfall amounts in the models, and so
localized flood impacts are certainly a possibility. Although
given the overall weakening of the system and very little to no
instability, rainfall rates will probably only be high enough to
result in a minor flood risk over just the most sensitive urban
areas or recent burn scar locations.

Chenard

Day 3
Valid 12Z Fri Feb 07 2025 - 12Z Sat Feb 08 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard


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