Mesoscale Precipitation Discussion 0651
NWS Weather Prediction Center College Park MD
115 PM EDT Mon Aug 13 2018

Areas affected...Central and Northern Texas...South Central OK...

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

Valid 131704Z - 132200Z

SUMMARY...Solid dynamics/confluence with weak remaining
instability may lead to new development that will have the
tendency to remain stationary/backbuild across saturated soils. 

DISCUSSION...GOES-16 imagery suite, depict stronger mid-level
shortwave lifting across northern TX panhandle into NW OK with the
trailing trof extending toward the Big Bend region.  Visible
imagery shows a weak inflection in/near the boundary layer in the
Martin/Midland region that is progged to remain relatively
stationary.  RADAR mosaic also denotes a washing out E-W oriented
outflow boundary across N Sterling to Runnels county, that is
intercepting 15-20kts of nearly orthogonal 850mb flow, supporting
weak isentropic ascent.  Low level stratus that dominated the
upstream environment has been eroding steadily.  This may help to
increase the current limiting factor (instability).  While 12z
soundings and RAP analysis depict some remaining instability, it
is below 1000 J/kg and given weak to moderate convergence, is
currently not sufficient for broad/strong updrafts, though there
are upward trends in Mitchell/Nolan county.   Still, modest
redevelopment/narrow updrafts provide .5-.75"/hr rain rates
(tropical rain showers).  This may be sufficient to maintain
ongoing high streams/flash flooding (given OU FLASH depicting up
to 500 cfs in the area). 

Given the low level unidirectional flow regime is aligned with the
deep tropical moisture plume per CIRA layered PWAT, totaling to
1.75 to 2", though increased low level moisture coming up the the
Rio Grande to Pecos River valleys supports total PWATS over 2" to
2.25".  To the West, the clearing as already increased instability
with MLCAPEs to 1500 J/kg at the Big Bend, nosing up to the
southern most convective cells in Glasscock county.  Given weak
850mb inflection near Garza county...may help to focus low level
convergence and redevelopment in the region to maintain this flash
flooding threat for the next 3-4hrs.

Further east, the environment was less worked over from last
evening and clearer skies supported a build up of instability with
SBCAPEs exceeding 2000 J/kg.  Limited convergence/forcing but aslo
equally weak capping has allowed for cells to develop with weak
convergence from Edwards county to Montegue county in North Texas.

With better forcing/mid-level confluence further west has allowed
for a bit of low level backing supporting a slow northward march
toward the mean trof.  This expands the area of concern for cells
to merge and potentially train across N Texas.  Given the narrow
nature of the updrafts and moving across areas not affected over
the past few days (higher FFG values), the potential for flash
flooding is to be isolated and more in urban centers given the
tropical moisture/warm cloud process  nature of these cells.  
 
Gallina

ATTN...WFO...EWX...FWD...MAF...OUN...SJT...

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

LAT...LON   34829719 33779655 32139757 30859899 30010025
            31020064 31560186 32220112 33109966