Mesoscale Precipitation Discussion 0796
NWS Weather Prediction Center College Park MD
658 PM EDT Fri Sep 07 2018

Areas affected...Central and Northeast Texas

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

Valid 072256Z - 080400Z

Summary...Flash flooding will remain possible from central into
north and northeast Texas this evening. A large number of heavy
rain bands and embedded thunderstorms remain active as of 6 PM CDT
in the general vicinity of a stalled front. Rain rates may reach 3
in/hr in some of the slower-moving and strongest rain bands.

Discussion...Numerous heavy rain bands and a few embedded
thunderstorms continued to affect much of Texas. The overall lack
of lightning was one signal that much of the convection had
dominant warm rain processes with high freezing levels, and
saturated profiles with tall, narrow CAPE. GOES-16 visible
satellite showed an outflow boundary pushing steadily southeast
over the northern half of Texas, and this was allowing for the
primary axis of convection to gradually push to the southeast as
well. However, the overall drift of this convection was likely not
fast enough to eliminate a flash flood threat. Rain rates
estimated by KFWS dual pol and MRMS were still reaching 2 in/hr in
some of the stronger rain bands, and this convection could affect
the DFW metro area (which would be more favored for flash flooding
given the larger amount of impervious surfaces). For North and
Northeast Texas, the greatest flash flood risk through 04Z should
be where convective bands intersect urban areas.

Further to the southwest, convective bands were moving more
slowly, which could be due to a weak low (circulation shown in
925-850mb layer on the RAP) over far northern Mexico, and an
associated deformation zone that extends up into the Concho
Valley. This region has seen heavy rainfall over the past week,
and flash flood guidance was reduced to as low as 1-2 inches in 3
hours. Given that hourly rain rates are easily reaching 1-2
inches, and even occasionally reaching 3 inches in the strongest
rain bands (per MRMS), there is an elevated chance of flash
flooding in this region. The combination of nearly stationary (at
times) rain bands, with highly efficient rainfall processes, in an
area with higher soil moisture already should lead to a greater
concentration of flooding issues and the potential for locally
more significant flooding. The Moderate Risk will be expanded
south into this area on a special update to the Day 1 Excessive
Rainfall Outlook to account for the increasing threat of flash
flooding.

Lamers

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

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

LAT...LON   33879627 33759468 33289416 32029522 31359656
            31009778 30589904 29750036 29350119 29700236
            30800296 31380122 32199918 33329771