AWUS01 KWNH 230901
FFGMPD
LAZ000-ARZ000-TXZ000-OKZ000-231500-

Mesoscale Precipitation Discussion 0306
NWS Weather Prediction Center College Park MD
500 AM EDT Thu May 23 2024

Areas affected...southeast OK into the Ark-La-Tex

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

Valid 230900Z - 231500Z

Summary...A compact MCS will produce heavy rainfall across
recently soaked portions of southeast OK into the Ark-La-Tex,
possibly resulting in isolated to scattered instances of flash
flooding.

Discussion...A cluster of thunderstorms that formed overnight in
southern OK has gradually organized into a compact MCS over the
past several hours, largely being missed by the recent 00z HREF
suite. While hi-res CAMs entirely failed to initiate convection in
a timely matter in this region, the mesoscale environment does
appear favorable for continued MCS maintenance and growth into the
early morning hours (which the 06z and 07z HRRR did finally pick
up on after a run or two of the model that failed to properly
assimilate the WSR-88d data). Looking downstream into the
Ark-La-Tex region, SPC mesoscale analysis indicates PWATs of
1.5-1.8 inches (above the 90th percentile, per SHV sounding
climatology), ML CAPE of 1000-1500 J/kg, and effective bulk shear
of 40-50 kts. Additionally, the storms appear positioned near a
quasi-stationary surface front with a diurnally strengthening
20-30 kt LLJ bringing ample low-level moisture transport. These
meteorological factors and parameter space suggest high
favorability for maintaining an MCS into the early morning hours
(as indicated by an MCS maintenance parameter of 90-100).

While the hi-res CAMs are not particularly useful in this case,
the latest HRRR runs do provide a decent depiction of what is
expected (though perhaps still a bit underdone in the overall
coverage and intensity of heavy rainfall compared to observational
trends). The expectation is for storms to become increasingly
organized and cold pool dominate, which would favor a more
southerly component to storm  motion (following the upwind
propagation vector towards the southeast, rather than the mostly
easterly dominate motion thus far). Concerns for localized flash
flooding are highest along the southern flank of the developing
MCS, where 1-3"/hr rainfall rates may have their greatest
residence time, resulting in localized totals of 2-4". Given that
the bulk of the region has seen at least moderate to heavy
rainfall over the past 6-12 hours (with localized totals of 2-4"
from the prior storms as well), isolated to scattered instances of
flash flooding are possible (with 3-hr FFGs still generally
ranging from 2-4". Should the MCS make it all the way into
northwest LA (and particularly into the Shreveport metro area)
where FFGs are generally 2.5" or less, flash flooding may be
locally significant.

Churchill

ATTN...WFO...FWD...LZK...OUN...SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...WGRFC...NWC...

LAT...LON   35489564 35269400 34039241 32749265 32479418 
            33189612 33789729 34509652 35169627 

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