024
AWUS01 KWNH 060143
FFGMPD
MSZ000-LAZ000-TXZ000-060600-

Mesoscale Precipitation Discussion 0571
NWS Weather Prediction Center College Park MD
942 PM EDT Fri Jul 05 2024

Areas affected...Much of Louisiana and Southwest Mississippi

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

Valid 060141Z - 060600Z

SUMMARY...Local rainfall rates to 3 inches per hour continue
across much of Louisiana into this evening. Flash flooding is
possible, particularly in urban areas.

DISCUSSION...Numerous cells of convection are ongoing across much
of Louisiana and southwest Mississippi this evening. PWATs remain
incredibly high...with SPC Mesoanalysis showing PWATs of 2.6
inches over Alexandria and 2.5 inches across much of the rest of
central Louisiana. Instability thus also remains high with SBCAPE
values in the pre-convective environment in southwest Louisiana
above 3,000 J/kg. Thus, with plenty of moisture and instability
available as well as an approaching cold front moving across
northern Louisiana...all the primary ingredients for continued
storm maintenance, despite the rapid loss of diurnal heating,
remain present. 850 mb flow is meager, less than 10 kt, as is the
surface southerly flow of moisture off the Gulf. Thus, there`s
nothing either adding or removing moisture from the thunderstorms.
Regardless...given the near record amounts of atmospheric moisture
present for the storms to work with...most of the strongest ones
don`t need an additional supply.

The storms have been moving generally southward...if
chaotically...over the past few hours. This is likely in response
to them "following the instability". However, the storms to the
north which would otherwise be cut off from the best instability
are maintaining themselves, especially during cell mergers...with
local rates across northern Louisiana still reaching up to 3
inches per hour. Thus, expect continued slow motion of the
heaviest convection to the south towards the Gulf, which is well
depicted in much of the CAMs guidance. FFGs are very high,
generally above 3 inches per hour, so flash flooding remains
possible as despite the locally high rainfall rates, their
occurrences have been very widely scattered.

Convection should begin dissipating from north to south as the
storms both exhaust the available atmospheric moisture and the
cold front dries everything out. All but widely scattered
convection should remain by around 06Z/1am CDT based on the latest
CAMs guidance.

The greatest threat for flash flooding continues to be where local
FFGs are lowered...i.e. urban areas. Thus, areas such as New
Orleans, Baton Rouge, Alexandria, and eventually Lake Charles may
have a locally increased flash flooding threat.

Wegman

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...JAN...LCH...LIX...SHV...

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

LAT...LON   32089336 32079210 31959160 31609056 30519030
            30348980 30028957 29379029 29819388 30899418
            31719410