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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2025Z Dec 07, 2022)
 
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
325 PM EST Wed Dec 07 2022

Day 1
Valid 16Z Wed Dec 07 2022 - 12Z Thu Dec 08 2022

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
THE SOUTHERN PLAINS EAST TO THE TENNESSEE VALLEY AND SOUTHERN
APPALACHIANS...

...16Z Excessive Rainfall Outlook Discussion...
Preliminary look at the 12Z guidance and the ensemble guidance
that arrived after the initial issuance of Day 1 outlook suggests
that the on-going outlook was in good shape and only minor
adjustments were needed.  The 09Z SREF showed a couple of members
with 2+ inch amounts in the deformation zone straddling the
Oklahoma/Kansas border...an idea supported more so by the GEFS. 
However, higher resolution guidance like the HRRR was focusing the
axis of heaviest QPF farther south.  As a result, opted to expand
the northern boundary of the MRGL just a bit northward.  Farther
east...expanded the Marginal Risk area a bit more northward given
on-going rainfall over eastern TN and the signal from the
operational guidance for upwards of an addition inch where terrain
and lower FFG may be met.  Given the modest deep-layer
instability...still think any problems should be isolated enough
to maintain the on-going Marginal Risk area.

Bann

...0830Z Excessive Rainfall Outlook Discussion...

...North Texas and Eastern Oklahoma eastward into the western
Tennessee Valley...
Models still suggest the potential for locally heavy to excessive
rainfall from parts of North TX into central-eastern Oklahoma and
across portions of the Lower MS Valley and TN Valley, though the
signal for anything other than an isolated (marginal) threat has
diminished considerably over the past couple of model cycles.
Aloft, a southern stream trough pivots across the Southwest U.S.
on Wednesday and across the High Plains Wednesday night. This
initial shortwave will be moving rather swiftly, given the
increased confluence (de-amplification of the shortwave with time)
by late Wednesday night. Given the flattening wave and more
west-east oriented front, the the degree and depth of
south-southwest low-mid layer flow will be somewhat restricted
(warm conveyor belt or WCB more compact). Moreover, limited
deep-layer instability (MUCAPEs 500-1000 J/Kg early dropping below
500 J/Kg later this afternoon and overnight) will also limit the
short-term rainfall rates. So despite a relatively quick bout of
robust low-mid layer moisture transport, with PW values topping
out between 1.5-1.7", the lack of instability along with
progressive nature of the favorable forcing (forward-propagating
Corfidi or MBE vectors) will lead to a more limited (isolated)
flash flood threat. In addition, per the latest NASA SPoRT
analysis, 0-100cm soil moisture percentiles are running between
10-30% of normal across much of the outlook area. As a result, the
Slight Risk area that was present in yesterday's Day 2 ERO has
been dropped to a Marginal.

Hurley



Day 2
Valid 12Z Thu Dec 08 2022 - 12Z Fri Dec 09 2022

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

Bann


Day 3

The Day 3 outlook will be updated by 2030Z.


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