Mesoscale Precipitation Discussion 0823
NWS Weather Prediction Center College Park MD
445 AM EDT Tue Sep 11 2018

Areas affected...Upper TX Coast...Ext Southwest LA...

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

Valid 110845Z - 111415Z

SUMMARY...Persisent redeveloping showers/thunderstorms with
efficient rainfall generation pose possible flash flooding through
early morning.

DISCUSSION...08z Surface analysis depicts an inverted trof/surface
wave between LBX and GLS along the surface front that remains
along the shore line from Aransas to this wave before angling
about 20 miles south of the LA coast line.  Strengthening western
Gulf surface and 850mb wind flow regime supports continued surface
based development with solid isentropic ascent above the boundary
layer to further enhance moisture flux and rainfall
rates/efficiency.  Aloft, the elongated shortwave/entrance to main
jet streak continues to exit over NE TX...this will keep deeper
trof axis generally stationary and favorably oriented to the
coast, while also supporting diffluence in weak upper level
outflow environment.  Though greatest upper level support will
continue to diminish with time.

In the short-term, thunderstorm expansion continues with training
cells along the effective warm front (east of the wave) into
Jefferson county and potentially will continue for a few more
hours.  With ample deep moisture with Tds in the upper 70s and
mean mixing rations near 17 kg/kg, total PWATs of 2.25" will
continue to support rates of 2-2.5"/hr.  The only drawback to
significant rainfall totals is slow southward/propagation into the
increasing low level flow.  This will push initiation points off
shore and tilt updrafts, the resulting isentropic ascent will
still be strong but without greater depth the rainfall
rates/totals should reduce with time as well.  Still, the
potential for an additional 2-4" totals may lead to some flash
flooding or fast rise inundation flooding through 14z.  

Gallina

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

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

LAT...LON   30199392 30119330 29759325 29659359 29449439
            29049501 28669561 28599586 28609601 29069607
            29459570 29899511 30159443