Mesoscale Precipitation Discussion 0745
NWS Weather Prediction Center College Park MD
1006 AM EDT Sun Sep 02 2018

Areas affected......South-Central to Southwest Louisiana...Upper
Texas Coast...

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

Valid 021405Z - 021805Z

Summary...Expanding area of convection within a highly favorable
thermodynamic environment north of a weak offshore low will lead
to spotty 2+ inch/hour rainfall rates this morning.

Discussion...The latest GOES-16 IR satellite imagery depicts a
concentrated area of cloud top cooling (deepening convection)
around a low pressure system centered offshore south of Lake
Charles. The thermodynamic environment is optimal for efficient
warm rain processes and high rainfall rates, as MUCAPES average
between 1000-2000 j/kg within a favorably deep moisture profile
(PWs over 2.25") per the observed 12Z RAOBs and latest SPC
mesoanalysis.

Helping to focus and maintain plumes of convection will be the
enhanced low-level inflow (20-25 kts at 925-850 mb) initially east
of the low-level circulation, pivoting westward toward the upper
Texas coast north of the low. This will maintain robust low-level
moisture transport, while also lead to back-building and training
of convection as the Corfidi vectors oppose the direction of the
low-level inflow. The one inhibitor to the flash flood threat
however is the absence of an inland frontal zone, which would help
to sustain the moisture convergence and strongest convection over
the same area for a more prolonged period of time.

Nevertheless, the deep warm cloud layer (wet bulb freezing levels
above 15kft per the 12Z KLIX and KLCH RAOBs), along with PWs
between 2.25-2.5" will continue to foster highly-efficient
rainfall rates -- likely exceeding 2"/hour within the strongest
and more persistent rain bands. Hourly FFG values are generally
above 2.5" initially, with 3 hourly FFGs over 3". The latest
mesoscale guidance, especially recent HRRR runs, indicate areas of
2+ inches/hour and 3-5+ inches within 3 hours within the outlook
area. This will lead to an enhancing flash flood threat toward
midday as the soils become more saturated with time.

Hurley

ATTN...WFO...HGX...LCH...LIX...

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

LAT...LON   30699197 30569123 29869044 29379018 28709023
            28669056 29239177 29429242 29599308 29579382
            29259459 29009510 29209535 29549536 29839503
            30099443 30059368 30049295 30349247