Flash Flood Guidance
Issued by NWS
Issued by NWS
971 AWUS01 KWNH 211628 FFGMPD TXZ000-OKZ000-KSZ000-COZ000-NMZ000-212230- Mesoscale Precipitation Discussion 1037 NWS Weather Prediction Center College Park MD 1227 PM EDT Sat Sep 21 2024 Areas affected...High Plains of New Mexico into the Panhandles of Texas and Oklahoma Concerning...Heavy rainfall...Flash flooding possible Valid 211630Z - 212230Z Summary...Showers and thunderstorms will expand in coverage through the afternoon while intensifying to feature rainfall rates nearing 1"/hr. Although storms will generally be fast moving, repeating rounds could result in 1-3" of rainfall and instances of flash flooding. Discussion...The GOES-E WV imagery shows an anomalously deep upper low moving over northern AZ with impressive downstream lift and moisture advecting into the southern High Plains of NM. Within this moisture plume, an area of moderate stratiform rain has lifted towards the TX Panhandle, while in its wake secondary convective development is gradually occurring as reflected by increasing glaciation in deepening cells noted via the day-cloud phase RGB. Rainfall from the morning precipitation has been as much as 0.5 inches measured by local mesonets, wetting the soils ahead of what should be increasing convective activity as PWs surge to 1.25-1.5 inches, and SBCAPE rises to 1000-2000 J/kg. As thermodynamics intensify through the aftn, forcing for ascent is also likely to become more impressive. The potent closed low and associated trough to the west will gradually push east, driving intense downstream divergence coincident with increasing upper diffluence over the southern High Plains. At the same time, unidirectional low-level southerly flow will begin to isentropically ascend the southward advancing cold front, and the overlap of these forcing mechanisms into the elevated PW/instability will result in widespread convective development as suggested by high-res simulated reflectivity. The HREF neighborhood probabilities indicate that rainfall rates have a 20-40% chance of exceeding 1"/hr in the deeper convection, with some storm organization through 40-50 kts of bulk shear helping to enhance and lengthen the duration of these rain rates in some areas. Although 0-6km mean winds will remain around 30 kts, suggesting progressive cell motions, aligned Corfidi vectors indicate a strong likelihood for repeating cells which could produce 1-3" of rainfall in some areas. 7-day rainfall for portions of northeast NM into the Panhandles of TX and OK has been as much as 400% of normal, leading to locally saturated 0-40cm soil moisture above the 95th percentile. While the progressive nature of these heavy rain rates should somewhat limit the flash flood potential this afternoon, any training or repeated rounds could cause impacts, especially atop the most saturated soils or across urban areas, sensitive terrain features, and burn scars. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ABQ...AMA...DDC...LUB...MAF...PUB... ATTN...RFC...ABRFC...WGRFC...NWC... LAT...LON 37220299 37090182 36810118 36080098 35610122 34730197 33830305 33340409 33480503 34320544 35280538 35370537 36400491 36940409