Mesoscale Precipitation Discussion 0826
NWS Weather Prediction Center College Park MD
357 AM EDT Wed Sep 12 2018

Areas affected......Coastal Southeast Texas...

Concerning...Heavy rainfall...Flash flooding likely

Valid 120800Z - 121400Z

Summary...Showers and thunderstorms continue over south Texas in
the vicinity of a low level stationary front.  Slow cell motion
leads to scattered areas of 2-5 inch rainfall amounts, with flash
flooding likely in areas where it has been raining heavily.

Discussion...An upper level trough is in place across south Texas.
 Showers and storms have developed near the boundary layer
moisture convergence and remnant surface front and associated
frontogenesis maxima depicted in the 06z RAP analysis and series
of forecasts into this morning.  The models show slow movement of
the upper trough to the east, continuing the threat through the
early morning hours.

The 00z Corpus Christi sounding shows a warm advection profile
with an impressive 2.3 inch precipitable water.  Light winds from
the SFC to 700 mb of generally under 15 kt lead to slow cell
motions.

The RAP shows boundary layer moisture convergence drifting west,
with the NAM and NSSL WRF showing redevelopment along the coast,
along with coastal convergence as the modest 15 kt inflow
persists.

Heavier rainfall rates are a result of the
anomalous moisture and areas of combined upper divergence/low
level convergence, including along the remnant frontal boundary.

High-res guidance shows a signal for 2-5" of rainfall across the
threat area, including the NCEP high res windows as well as the
Canadian regional GEM and 00z NSSL WRF. 3-hr FFG guidance in south
Texas is variable with a stripe near 2 inches in 3 hours, which
appears to be likely given initial slow cell motions and high
available moisture to tap.

Petersen

ATTN...WFO...BRO...CRP...HGX...

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

LAT...LON   29119588 28739556 28379597 27779672 27029708
            26019730 26019799 27409814 28239798 29049657