Mesoscale Precipitation Discussion 0949
NWS Weather Prediction Center College Park MD
1043 PM EDT Mon Oct 08 2018

Areas affected...South-Central TX

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

Valid 090240Z - 090840Z

Summary...Very heavy rainfall is expected on a rather small scale
tonight over portions of south-central TX with very slow-moving
showers and thunderstorms. Some flash flooding will be likely.

Discussion...The radar imagery is showing a small cluster of very
slow-moving showers and thunderstorms across portions of
south-central TX, with an emphasis on Frio county. Cloud tops over
the last 45 minutes have tended to cool a bit and the convection
is focusing within a moderately unstable airmass with MUCAPE
values of 1500 to 2000 j/kg. Meanwhile, persistent low-level
southeast flow continues to maintain plenty of moisture in off the
Gulf of Mexico, and the PWATS across the region are near or
slightly above 2 inches.

The upper-level flow across south-central TX is rather diffluent
as a result of a deep layer trough over the Four Corners region
which is edging out into the southern High Plains. This is
providing at least some modest deep layer ascent over the region
that is helping to sustain the convective threat given otherwise
favorable thermodynamics.

The last couple runs of the HRRR have been showing some very heavy
rainfall potential, with the idea of seeing a rather small scale
area of very slow-moving convection. Given the deep layer moisture
profiles, it certainly appears quite plausible to see enhanced
rainfall totals as the rainfall rates will be very high with
hourly amounts of as much as 2 to 3 inches.

Expect storm totals to locally be as much as 4 to 6 inches given
the high rain rates and slow movement. This will likely result in
some flash flooding. Will continue to closely monitor through the
night.

Orrison

ATTN...WFO...CRP...EWX...

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

LAT...LON   30609865 30269783 29219816 28749868 28579898
            28509933 28709970 29019989 29729971 30289928