STORM2K

Mesoscale Precipitation Discussion 0972
NWS Weather Prediction Center College Park MD
748 PM EDT Fri Oct 12 2018

Areas affected...Western & Central TX

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

Valid 122347Z - 130547Z

Summary...Thunderstorms are increasing in coverage across the area
ahead of Sergio's remnants. Hourly rain totals to 1.75" and local
amounts to 4" are possible prior to 06z.

Discussion...Satellite imagery reveals the remains of Sergio near
30N 108.5W, about 160 miles west-southwest of El Paso. The
environment ahead of the system is moistening, with precipitable
water values of 1.25-1.75". The activity is near and just north
of a thermal boundary lying across the region, which has ML CAPE
values of 500-1500 J/kg. While inflow at 850 hPa is 10-15 kts per
VAD wind profile data, effective bulk shear of 30-55 kts lies
here, which appears to have led to the development of a
mesocyclone well south-southwest of Midland TX. Showers and
thunderstorms have been festering in central TX and showing signs
of greater organization in and near western TX.

The expectation is for convection to fill in and increase in
intensity in time across two areas: near the Texas Big Bend/Pecos
River Valley and in the vicinity of the northern Concho Valley.
After 03z, convergent low-level inflow is expected to increase
which should import greater moisture into the region The 18z HREF
probabilities of exceeding 1" an hour peak in the 03-04z time
frame near the Concho Valley and are high after 03z as the remains
of Sergio move into the Trans Pecos region. The portion of the
boundary is western TX is expected to lift somewhat to the north
in the meantime. The HRRR/RAP guidance appear well behind the
curve concerning the recent uptick near the Concho Valley, so the
heavy rainfall could occur sooner than advertised. Hourly rain
totals to 1.75" with local amounts to 4" are anticipated. Soils
have been saturated by recent rainfall totaling over 300% of
normal. Flash flooding is a concern.

Roth

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

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