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Flash Flood Guidance
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Issued by NWS
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377 AWUS01 KWNH 180001 FFGMPD AZZ000-UTZ000-180329- Mesoscale Precipitation Discussion 0893 NWS Weather Prediction Center College Park MD 800 PM EDT Sat Aug 17 2024 Areas affected...South-Central Utah, northern Arizona Concerning...Heavy rainfall...Flash flooding likely Valid 172359Z - 180329Z Summary...Considerable impact flash flooding will continue across south-central Utah and northern Arizona past 0z as additional cells with .75-1"/hr rainfall rates persist for a few more hours. Discussion...Throughout the afternoon, training showers and thunderstorms with 0.75-1"/hr rainfall rates have produced numerous instances of considerable impact flash flooding across south-central Utah and northern Arizona. In a region of generally high radar quality in southern Utah and northern Arizona, rainfall estimates of 1-1.25" are noted over the last six hours where the most intense cells have trained. Upstream of the current storms, trends in the Day Cloud Phase RGB and experimental LighningCast suggest additional development is underway in a cumulus field over north-central Arizona. In spite of some overturning by the convection, steep mid-level lapse rates and plentiful moisture transport into the region continue to support 1000-2000 J/kg of MUCAPE and 1.1-1.2" PWATs (above the 90th percentile for FGZ and GJZ) near the storms per RAP and objective analysis estimates. Effective shear remains impressive as well, with 40-50 kts noted. Aided by strong upper diffluence and a weak shortwave near the Four Corners, periods of training convection should continue for a few more hours across the region before eventually diminishing with loss of daytime heating. Through 3Z, HREF neighborhood probabilities maintain a 20-35% chance of rainfall rates exceeding .5"/hr. In light of ongoing impacts, this will continue the flash flooding threat (some of which could be significant) for another few hours. Asherman ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...FGZ...GJT...SLC...VEF... ATTN...RFC...CBRFC...NWC... LAT...LON 40381221 39821035 37180989 35461092 35151246 35901369 37211399 39321350