795
AWUS01 KWNH 222109
FFGMPD
TXZ000-230215-

Mesoscale Precipitation Discussion 1043
NWS Weather Prediction Center College Park MD
509 PM EDT Sun Sep 22 2024

Areas affected...Big Bend into northwestern TX

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

Valid 222107Z - 230215Z

Summary...Increasing flash flood potential will setup across
portions of Big Bend into the Permian Basin and northwestern TX
through 02Z. Rainfall rates of 1-2 in/hr, but locally in excess of
2 in/hr, are expected to lead to a couple of 3-4" totals.

Discussion...Surface observations from 21Z and visible satellite
imagery helped place a cold front across western TX, with an
attached surface low just south of a MAF to BPG line. Convective
development was increasing along the portion of the front
extending northeast of the surface low, while development near the
weaker cold frontal segment to the southwest of the low was
isolated. 20Z SPC mesoanalysis data showed plenty of instability
in place south of the front with 1000 to near 3000 J/kg MLCAPE
(highest near Rio Grande) along with 1.4 to 1.8 inches of
precipitable water.

Lift across the region was occurring ahead of an advancing
positively tilted upper trough axis extending from the central
High Plains into the Desert Southwest and the right entrance
region of an associated 70-90 kt jet max near 250 mb. Short term
model forecasts show the front continuing to advance gradually off
toward the southeast over the next 3-6 hours into weak
southeasterly low level winds. Surface convergence and forcing
aloft, coupled with the available instability, should be enough to
support increasing convective coverage throughout the remainder of
the afternoon and through the evening, especially between I-10 and
I-20 where mean steering flow will be roughly parallel to the
front, allowing for repeating and merging of cells along with
rainfall rates of 1-2 in/hr (locally in excess of 2 in/hr
possible).

Farther south, coverage of convection may remain more isolated,
especially in the vicinity of Big Bend N.P. where forcing is
weaker and some pockets of weak inhibition likely remain. However,
speed shear profiles will support some organized, possibly slower
moving, cells. The potential for merging cells will also exist
farther south, but this is conditional on higher coverage
occurring closer to Big Bend. Despite dry antecedent conditions
over roughly the past 3 weeks, at least isolated flash flood
potential will exist across northwestern TX into the Big Bend
region where a couple of 3-4" totals may occur.

Otto

...Please see www.wpc.ncep.noaa.gov for graphic product...

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

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

LAT...LON   33729859 32849831 32029859 31079965 30550040
            29920157 29560234 29280254 29000277 28820309
            28780346 28930371 29060390 29380406 29620412
            29790420 30210429 30510423 30620403 30470357
            30580305 31150249 31880211 32710136 33320000
            33649925