Flash Flood Guidance
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Issued by NWS
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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