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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2032Z Feb 25, 2024)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 PM EST Sun Feb 25 2024

Day 1
Valid 16Z Sun Feb 25 2024 - 12Z Mon Feb 26 2024

...16Z Update...

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

Wegman


Day 2
Valid 12Z Mon Feb 26 2024 - 12Z Tue Feb 27 2024

...2030Z Update...

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

Wegman

Day 3
Valid 12Z Tue Feb 27 2024 - 12Z Wed Feb 28 2024

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

...2030Z Update...

Few changes were made to the existing Marginal Risk area across
the Ohio Valley. Latest guidance suggests the heaviest rainfall
totals will be overnight Tuesday night/Wednesday morning across
far northern Ohio, southeast Michigan, and northwestern
Pennsylvania. As such, the Marginal was expanded a bit towards the
northeast. A 60 kt LLJ is forecast in multiple pieces of guidance,
including the GFS and EC, which will advect Gulf of Mexico
moisture and instability northeastward ahead of a low and strong
cold front racing east across the Plains. Much of the thunderstorm
activity will be associated with the warm front and the LLJ behind
it. Largely unidirectional southwesterly flow will favor the
development of training thunderstorms in the Marginal Risk area.
The strongest storms are expected on the western side of the
Marginal Risk area as the storms are moving across Illinois and
Indiana Tuesday afternoon and evening. By the time the storms
reach eastern OH and western PA, the focus will be the leading
edge of the LLJ and the warm front, resulting in a larger area,
perhaps as an MCS of moderate to locally heavy rain. Expect more
widespread 1 to 2 inch totals in this area, but less likely to see
the extreme but highly localized rainfall totals more likely
further west.

The biggest factor working against flash flooding is the prevalent
bone-dry conditions over the entire Marginal Risk area leading up
to this event. This should allow added "space" for the rainfall to
fill largely empty river basins. Nonetheless, the potential for
heavy rainfall with the favorable atmospheric conditions should
overcome the dry soils in isolated instances. The Marginal remains
lower confidence.

Some of the model guidance suggests heavier convection could
develop further south towards the Ohio River itself, so there is
some potential for additional expansions towards the river.

Wegman

...Ohio Valley...

A strong positively tiled mid-level trough is expected to sweep
across the Central U.S. Tuesday/Tuesday night with a potent area
of low pressure likely to intensify over the Great Lakes. A warm
front draped across the region will act as the focus for elevated
showers and thunderstorms as early as the afternoon hours, and
likely continue through the night as a very impressive low-level
jet ramps up where 850 mb winds reach 50+ kts. This warm/moist
airmass will spark scattered/numerous showers and thunderstorms
along the advancing cold front Tuesday night through early
Wednesday morning. This system will have very strong dynamics and
an increasingly moist airmass which may be supportive for locally
heavy rainfall, particularly along the warm front where
training/repeating rounds of rainfall are more likely. The storm
motions are likely to be fast/progressive along and ahead of the
cold front but may contain intense/brief rain rates. While there
remains uncertainty in the placement/timing of the main features,
the setup certainly favors strong thunderstorms and with the PWs
increasing well above 1", some localized/isolated flooding issues
will be possible so a Marginal Risk was introduced this cycle for
portions of the Ohio Valley.

Taylor



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