Flash Flood Guidance
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Issued by NWS
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401 AWUS01 KWNH 221800 FFGMPD LAZ000-ARZ000-TXZ000-OKZ000-230000- Mesoscale Precipitation Discussion 0303 NWS Weather Prediction Center College Park MD 159 PM EDT Wed May 22 2024 Areas affected...North Texas through the ArkLaTex Concerning...Heavy rainfall...Flash flooding possible Valid 221800Z - 230000Z Summary...Showers and thunderstorms will expand in coverage through the afternoon while organizing ahead of a cold front. Rainfall rates will likely reach 2-3"/hr, with briefly higher rates possible, producing 2-4" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon indicates rapid expansion of reflectivity associated with intensifying convection from North Texas through the ArkLaTex and into southern AR. This convection is blossoming in a region of extreme thermodynamics characterized by PWs of 1.7 to 1.9 inches, and a ribbon of MLCAPE exceeding 4000 J/kg. This MLCAPE is being produced thanks to a robust EML noted in the 12Z FWD U/A sounding, with LIs around -10 further evidence of the intensity of this environment. Although the area appears to be in the less-favorable RFQ of a jet streak to the north, strong low-level convergence along the front, weak PVA ahead of an impulse rotating through the flow, and at least modest 850mb convergence on the nose of an intensifying surge out of the Gulf of Mexico will likely allow showers and thunderstorms to continue to expand and strengthen. Rainfall rates of 1-1.5"/hr have already been estimated via KFWS WSR-88D. During the next several hours, the cold front will waver near the Red River Valley of the South as a wave of low pressure moves along it to the east. This will produce enhanced lift through convergence, which will act upon the extremely unstable environment to expand convective coverage, and likely lead to more intense rainfall rates. This is reflected by HREF neighborhood probabilities for 2"/hr reaching as high as 60%, with the HRRR 15-min rainfall suggesting brief 4"/hr rates likely, especially where storms become most organized in the presence of more than 50 kts of bulk shear. This will likely lead to supercells and clusters, which could grown downstream into a complex over southern AR as noted in recent ARW and HRRR runs. While rainfall rates may be most intense in any supercells, the organization into clusters could prolong the duration of these rainfall rates, and this will likely produce more than 3" of rain in many areas as noted by HREF probabilities exceeding 70%, with 5" or more possible where multiple rounds of storms occur. Training and backbuilding upstream into the higher instability across North Texas is also expected. Recent rainfall, using the 7-day AHPS as proxy, has been well below normal across much of this region. This has allowed FFG to recover to 3-4"/3hrs which has only a 10-20% chance of exceedance according to the recent HREF. Still, the likelihood of intense rain rates and storm organization, along with the potential for multiple rounds or some upstream training, could still produce instances of flash flooding into this evening. Weiss ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...FWD...LZK...OUN...SHV...TSA... ATTN...RFC...ABRFC...LMRFC...WGRFC...NWC... LAT...LON 35039405 34929329 34629266 33989227 33389233 33129273 32669392 32239549 32069716 32079801 32329833 32549843 33089835 33589810 34139737 34459676 34869566