Mesoscale Precipitation Discussion 0781
NWS Weather Prediction Center College Park MD
1215 PM EDT Thu Sep 06 2018

Areas affected...Central Oklahoma; North Texas

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

Valid 061614Z - 062200Z

Summary...Scattered thunderstorms and rain bands are expected to
develop this afternoon across the Southern Plains in an area of
very weak winds. This should allow storms and areas of rain to
move very slowly, with the potential for locally heavy rainfall.
Rain rates exceeding 2 in/hr will be possible, which could lead to
flash flooding.

Discussion...The environment from North Texas into central
Oklahoma is characterized by deep moisture, with RAP analyzed PWs
around 2.2 to 2.3 inches. These were quite close to (perhaps a bit
higher than) GPS-PW observations, and were also easily above the
95th percentile for this time of year. Additionally, the wind
fields across the region were very weak, with the deep layer mean
winds less than 10 knots, and Corfidi vector magnitudes around 5
knots. The CAPE profiles, as sampled by 12Z soundings from Norman
and Fort Worth, were tall and narrow with MLCAPE around 1000 j/kg.
These factors should all combine to yield slow-moving or nearly
stationary, shallow convective rain bands that should be efficient
rainfall producers and create localized very heavy rain rates.
Recent runs of the HRRR show a scattered nature to the convection,
but localized rain rates in excess of 2 in/hr, which could lead to
flash flooding. There is not a tremendously strong convective
focus to concentrate rainfall in a particular area, but the slow
storm motions and storm-scale processes and interactions should be
sufficient to yield a few areas with at least several inches of
rain and flooding issues. Based on the 12Z HREF and recent runs of
the HRRR, initial development appears likely from western North
Texas (near SPS) into central Oklahoma, where cloud top heights
have been increasing (per GOES-16 data) and there is greater cloud
development overall. After 21Z, this could expand into the rest of
North Texas.

Lamers

ATTN...WFO...FWD...OUN...SJT...TSA...

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

LAT...LON   36059721 35279617 34299613 33289646 32249717
            32269846 33019947 34099947 35299874