AWUS01 KWNH 230914
FFGMPD
TXZ000-NMZ000-231500-

Mesoscale Precipitation Discussion 0964
NWS Weather Prediction Center College Park MD
513 AM EDT Wed Aug 23 2023

Areas affected...West Texas

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

Valid 230900Z - 231500Z

Summary...Locally heavy rainfall (with rates of 1-2"/hr) in
association with Tropical Depression Harold is expected to lead to
localized short-term totals of 2-4". Isolated to widely scattered
instances of flash flooding are possible.

Discussion...Tropical Depression Harold continues to trek
west-northwestward through northeastern Mexico, now entering the
higher terrain of the Chihuahuan Desert. Deep persistent
convection (per GOES-East infrared imagery) has been ongoing to
the north-northwest of the center of Harold, and this convection
is beginning to move into the West Texas portions of the
Chihuahuan Desert. Rainfall rates in association with this deep
convection are likely on the order of 1-2"/hr, as radar coverage
across this region of West Texas is poor (even when the currently
down KMAF radar is operating). The MRMS RQI (radar quality index)
for the Texas Big Bend and northward into the Trans-Pecos is near
0%, indicating unreliable radar observations (with the nearest
beams scanning far too high up in the troposphere to be of
reliable use for precipitation estimates). Despite the poor radar
coverage and quality, a period of locally heavy rainfall is
expected from morning to mid-day across much of West Texas, as the
center of Harold continues to track northwestward (at near 12 kts,
per the latest 09z WPC advisory).

Hi-res model guidance (including the 00z HREF and more recent HRRR
runs) is in rather good agreement concerning expected rainfall,
suggesting localized totals of 2-4" through 15z. The most favored
corridor for these higher amounts extends across much of Brewster
into western Terrell, southern Pecos and Reeves, and eastern Jeff
Davis and Presidio counties. The 00z HREF 40-km neighborhood
probabilities for 2" and 3" thresholds are between 30-50% and
15-25%, respectively, and the HRRR runs since 00z depict the
heaviest totals in these areas as well (consistent with
observational trends in the deep convective activity). The bulk of
this rainfall is expected to occur over a 3-hr period, with
associated Flash Flood Guidance (FFG) generally ranging from 2-4".
Since this would require the precipitation to fall in the most
hydrologically sensitive spots (which is primarily in the vicinity
of Fort Davis and points northwestward into far West TX) to exceed
FFG, isolated to widely scattered instances of flash flooding are
considered possible.

Churchill

ATTN...WFO...EPZ...EWX...MAF...

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

LAT...LON 32330552 32120432 31660331 30620196 29400140
28090174 28390315 29210475 29930592 30910697
32040674

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