Quantitative Precipitation Forecast
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FOUS30 KWBC 140843
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Sat Apr 14 2018

VALID 12Z Sat Apr 14 2018 - 12Z Sun Apr 15 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 N KEHC 15 NW KVNP 30 WSW HEZ 20 N GWO 40 NNE MKL 15 E EVV
10 NNE EYE 10 S MIE 10 SE KI68 15 E SME 15 NNW RHP LZU 10 N CSG
10 SSW DHN 25 WSW PFN 90 SSW PAM.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 N KVQT 10 E KVNP 15 NE HEZ 25 SSE TVR 40 WNW GTR 35 SE MKL
25 SE CKV 25 NNW GLW 20 SW EKQ 25 N CHA 20 NNW RMG 25 ESE ANB
25 SW TOI 40 S NPA 20 S KIKT.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 NNE MOB 20 NNW BIX NEW 25 NE 7R3 20 SSW BTR 15 WNW MCB
35 NNE MCB 35 ESE JAN 30 SSW GTR 20 ENE CBM 10 SSW 1M4
25 SSW 3A1 25 ENE BHM 25 NW ALX 15 N MXF 20 NNW GZH 45 NNE MOB.


...Lower MS Valley into the TN and OH Valley and Southeast...

As of 08z this morning a convective line stretches from IN south
into the Lower MS Valley and into east TX...with the heaviest
amounts focusing across southeast AR into northwest MS where some
training will continue into the early morning hours. Indications
are that this convective line will become more progressive by 12z
as it continues to push eastward. In general the line is forecast
to remain progressive through the day 1 period...likely limiting
the potential for any extreme rainfall amounts. With that said,
still think some slowing of the line is likely by this afternoon,
resulting in a corridor of enhanced flash flood potential. As the
shortwave energy over the Plains digs into the MS Valley this
afternoon the entire trough will take on more of a negative tilt.
This should act to slow the forward progression of the line across
portions of southeast LA into southern MS and much of AL. The
expectation is that the digging wave and negatively tilted trough
will aid in upstream convective development that will expand along
the already present eastward moving convective line. Thus, even
though the line will maintain some movement east, the slowing of
it and upstream development will allow for some southwest to
northeast training of the cells embedded within the line. Moisture
parameters will remain impressive...with strong 850 mb moisture
transport and PWATs approaching climatological max values. Thus
any training would present a flash flood threat.

WPC QPF for the warm sector of this system generally blended the
HRW ARW, ARW2 and the HREF Mean. The HRRR was also heavily used
early in the period, as it was the best match of the high res
guidance to the current radar. The ARW was also a good match,
although feel like it may become a bit too progressive by later
today. Thus incorporated some of the slower ARW2 and HREF mean to
account for this. Given that organized convection is ongoing and
will maintain through the day...generally stuck with the high res
guidance for this warm sector QPF...as it is situations such as
this when they typically are much more useful than the global
guidance.

Given these preferences, only minor changes were made to the
Moderate risk, which extends from southeast LA into southern MS
and central AL. Would anticipate the aforementioned training
potential to result in localized 5"+ amounts within this Moderate
risk area...resulting in a flash flood threat today. Amounts were
decreased some from northern AL into the OH Valley. Instability
will be less here and the orientation of convection further south
may help cut back on totals over this area as well. For this
reason did nudge the Moderate risk south out of northern AL, and
also cut back some on the northern extent of the Slight over the
OH Valley.

Chenard

$$





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