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AWUS01 KWNH 301012
FFGMPD
MSZ000-LAZ000-ARZ000-TXZ000-OKZ000-301610-

Mesoscale Precipitation Discussion 0687
NWS Weather Prediction Center College Park MD
611 AM EDT Tue Jul 30 2019

Areas affected...Arklatex into LA and central MS

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

Valid 301010Z - 301610Z

Summary...Increasing flash flood potential will exist through the
remainder of the morning across portions of the Arklatex into LA
and central MS. Locally very heavy rainfall in excess of 6 inches
will be possible with training a growing concern.

Discussion...Regional radar imagery as of 0945Z showed a small
cluster of convection expanding across portions of central LA
along with scattered showers expanding in coverage over
northeastern TX into northern LA. VAD wind plots at 700 mb
combined with RAP analyses indicated two shortwave troughs which
seem to be the forcing mechanisms for the recent convective
development. One of these troughs extended from southeastern MO
into northeastern TX, while the other from north-central MS into
southwestern LA. Precipitable water values ranged from 1.7 to 2.2
inches across the region via recent GPS data. The convection
appears to be elevated in nature for the moment, rooted between
850 and 700 mb, taking advantage of an estimated 500-1500 J/kg
MUCAPE as per the 09Z SPC mesoanalysis page.

Slow storm motions of ~10 kt or less combined with northwesterly
flow aloft will aid in training of cells given nearly
unidirectional flow aloft, some of which has already been observed
in Evangeline and Avoyelles Parishes through 0945Z. With the onset
of daytime heating after sunrise, further increases in instability
are expected with little in the way of capping. This should lead
to an increasing coverage of convection over the next few hours
over LA into portions of central MS with forcing ahead of the 700
mb trough axes likely playing a key role in development.

The 00Z suite of hi-res models along with subsequent runs of the
HRRR have been unanimous in producing over 6 inches of rain from
north-central LA to central LA. However, the coverage of heavy
rain from the guidance appears overdone and recent runs of the
HRRR (07Z, 08Z, 09Z) have trended drier with rainfall totals
through 16Z. Therefore, confidence in exact placement and coverage
of heavy rain is a bit uncertain. Still, the magnitude of
moisture, slow storm motions and sufficient CAPE support
potentially very heavy rainfall with localized totals of 3-6
inches through 16Z with possible flash flooding.

Otto

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

ATTN...WFO...FWD...JAN...LCH...LIX...LZK...SHV...

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

LAT...LON   34019459 33919373 33499316 32719219 32689164
            33499035 33498992 33168932 32708909 32048938
            30599132 30329245 30679369 31939464 33319536



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