Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri May 12 2023 17:54:02

AWUS01 KWNH 121753
FFGMPD
TNZ000-ALZ000-MSZ000-LAZ000-ARZ000-122350-

Mesoscale Precipitation Discussion 0273
NWS Weather Prediction Center College Park MD
153 PM EDT Fri May 12 2023

Areas affected...portions of the Lower Mississippi and Tennessee
Valleys

Concerning...Heavy rainfall...Flash flooding possible

Valid 121750Z - 122350Z

SUMMARY...Localized training of convection in the vicinity of an
outflow boundary may produce localized flash flooding from
northern LA/southern AR into central/northern MS, northern AL and
southern TN over the next 3-6 hours. Rainfall rates of 1-2 in/hr
and 2-4 inch totals are expected, but coverage of these higher
amounts is forecast to remain limited.

DISCUSSION...1730Z visible satellite imagery showed an outflow
boundary extending from near the AR/LA border into northern MS and
south-central TN. To the west of a ridge axis over MS/AL, Well
defined cloud streets were observed from the west-central Gulf
Coast into northern LA and western MS, intersecting the southward
sagging outflow boundary with recent development noted just north
of GWO and attempts at initiation over northern LA. A local max
was noted in GPS-derived precipitable water values over northern
LA with 1.6 to 1.9+ inches and the 17Z SPC mesoanalysis showed
MLCAPE near 3000 J/kg along the LA/AR border and MUCAPE of
1000-2000 J/kg behind the outflow boundary from western TN into
northwestern TN.

Recent CAM guidance has struggled to handle the ongoing evolution
of mesoscale boundaries and subsequent convection well but with
southwesterly steering flow quasi-parallel to the orientation of
the outflow boundary, there could be some areas of training with
storms that develop. VAD winds at 850 mb over LA/MS were 25-30 kt
at 17Z but are forecast to weaken into the afternoon, especially
over MS as low level ridging builds westward. While mid-upper
level flow is weak and storms should not be very organized, there
will be a localized threat for flash flooding with areas of
training (1-2 in/hr rates) and localized totals of 2-4 inches
through 00Z. Portions of the region have experienced well above
average rainfall over the past few days, increasing potential for
excess runoff.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6N7eUiV0bCPrRct-k0NoZcPEQxc17ppml_dqCFtWMB2IlwhqpzE4E2zpImyAwe46HqJc=
GEU7DuR144hO-Jz9Eee1FFE$  for graphic product...

ATTN...WFO...BMX...HUN...JAN...LZK...MEG...OHX...SHV...

ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...

LAT...LON   35818736 35758640 35558600 35048599 34588627=20
            34018691 33488781 32149007 31779228 32169330=20
            33159319 33379204 33939072 34798890=20

=3D =3D =3D
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