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Flash Flood Guidance
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Issued by NWS
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129 AWUS01 KWNH 092157 FFGMPD TNZ000-KYZ000-INZ000-ILZ000-100300- Mesoscale Precipitation Discussion 0600 NWS Weather Prediction Center College Park MD 556 PM EDT Tue Jul 09 2024 Areas affected...portions of the Ohio Valley Concerning...Heavy rainfall...Flash flooding possible Valid 092155Z - 100300Z Summary...Training/repeating rainfall rates of 1-2"/hr may lead to localized totals of 3-5". Isolated to scattered instances of flash flooding are possible. Discussion...Post-tropical cyclone Beryl is tracking northeast at 24 mph across the MS/OH Valleys this afternoon, and convection has become focused primarily east of the center (both along the warm front and across the warm sector (post-frontal). Discrete supercells have become the most efficient rainfall producers, with rainfall rates of 1-2"/hr. Otherwise, convection is generally producing rates of 1"/hr or less (with stratiform rainfall north of the center generally producing 0.5"/hr or less). Along and ahead of the warm front, the mesoscale environment is characterized by ML CAPE of 1000-2000 J/kg, precipitable water values of 2.0-2.3 inches (near record values, per SPC sounding climatology from surrounding sites), and ample effective bulk shear of 45-55 kts. With convection is remaining rather progressive due to the strong dynamics of this post-tropical system, there is a distinct risk of localized training/repeating of heavy rainfall rates (1-2"/hr) in and around the aforementioned warm front (stretching from southern IL across the IN/KY border region). The 18z HREF probability matched mean QPF depicts localized totals of 3-5" (with corresponding 40-km neighborhood probabilities for 3" exceedance of 20-30%). A much broader region to the north and east of the cyclone has relatively high odds of localized 2" exceedance (per 40-km neighborhood probabilities of 40-70%), and corresponding Flash Flood Guidance (3-6 hr) generally ranges from 2-3". As a result, isolated to scattered instances of flash flooding are possible (with the greatest risk over southeast IN and adjacent portions of IL/KY). Churchill ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...ILN...ILX...IND...LMK...LOT...LSX...OHX...PAH... ATTN...RFC...LMRFC...NCRFC...OHRFC...NWC... LAT...LON 40708771 40468699 40008630 39578588 38888511 37718531 36608585 36338744 36668815 37898853 39648992 40328948 40648867