Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FOUS30 KWBC 141448
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1047 AM EDT Sat Apr 14 2018

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


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SW SRN 10 E 7R4 20 ENE LFT 25 ESE HEZ 40 N GWO 45 SSE PAH
10 ESE EVV 20 WSW AID 25 WNW DAY 25 SSW ILN 20 SE SME 20 WNW RHP
PDK 20 ENE DTS 45 SE KVOA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 N KEIR 15 NE SRN 25 ENE ARA 20 W MCB 10 WSW HKS 15 ENE GWO
35 SE MKL 25 S CKV 15 SE BWG 20 SE K8A3 10 NNW DNN 25 W LGC
10 NNW CEW 10 SSW RAM.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N MOB 10 SSW HSA MSY 30 N 7R3 MCB 30 SE JAN 20 SSW GTR
25 S 1M4 15 N BHM 20 NW ALX 15 WSW MGM 30 N MOB.


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

1500 UTC update...

Previous outlook area remains on track -- as changes with the 15Z
issuance were mainly cosmetic, largely paring the back edges of
the MODERATE and SLIGHT risk areas based on the latest composite
radar imagery, mesoanalysis, and short-term HRRR/experimental HRRR
trends. Have also ensured the MODERATE area encompasses the area
where the latest (06Z) HREF depicts the highest probabilities of
3-hourly QPF>3 inches (40-70+ percent).

Hurley


Previous discussion below...

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

$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.