Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 23 2024 01:04:30 AWUS01 KWNH 230104 FFGMPD COZ000-NMZ000-AZZ000-UTZ000-230630- Mesoscale Precipitation Discussion 0923 NWS Weather Prediction Center College Park MD 903 PM EDT Thu Aug 22 2024 Areas affected...Northern Arizona and far Southern Utah Concerning...Heavy rainfall...Flash flooding possible Valid 230103Z - 230630Z Summary...Showers and thunderstorms will continue for several more hours as they lift across northern Arizona and into Utah. Rainfall rates may at times exceed 1"/hr, leading to sub-hourly rainfall as much as 0.5-0.75" and isolated total rainfall up to 2". Flash flooding is possible. Discussion...The GOES-E visible imagery this evening is still sufficient to reflect fresh Cu and TCu development across much of central and northern Arizona, with the day-cloud phase RGB indicating rapid growth to glaciation also occurring. This suggests that there is still plentiful instability for updraft intensification, which is supported by SPC RAP analysis MLCAPE of 1000-1500 J/kg. This robust instability is collocated with anomalous moisture reflected by GPS measured PWs of 1-1.4 inches, around the 75th-90th percentile for the date for this area. A shortwave lifting northward towards the Mogollon Rim is interacting with a strengthening jet streak to the NW to produce robust deep layer ascent into the Four Corners. While is it likely convective overturning and rapid approach of nightfall will cause a slow wane of instability, the high-res CAMs indicate that several more hours of active convection is likely. This is in response to the deep layer ascent offsetting the relative loss of instability, especially in the presence of strong moisture flux noted by SREF 850-700mb anomalies reaching +4 sigma by 06Z. New storms that develop will likely move N/NE on 0-6km mean winds of 15-20 kts, but aligned Corfidi vectors and 20-30 kts of effective bulk shear suggest some organization and redevelopment into the greater thermodynamics could result in short-term training. Rain rates are progged by the HREF neighborhood probabilities to have a 15-25% chance of reaching 1"/hr, which could result in sub-hourly rainfall of 0.5 to 0.75 inches as depicted by the UA HRRR WRF and HRRR 15-min rainfall product. These rates could be more than sufficient to produce rapid runoff leading to instances of flash flooding, especially across any vulnerable terrain features like slot canyons, dry washes, or burn scars. However, the aforementioned short-duration training potential also suggests that locally 1-2" of rain could occur in some areas. Soils across the region have 0-10cm RSM that is measured above 95% by NASA SPoRT, suggesting that heavy rain will struggle to infiltrate into soils across most of the area. This indicates that rapid runoff leading to instances of flash flooding are possible anywhere that training of these impressive rain rates occurs until intensity dwindles later tonight. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8ruXWNFNMYSp5KD4oHZN8qHuTYSp2Cc-Rs81l2IVfBGIoXtfb7lDsm9l0jtopeCUaKmZ= Oz-ISHXQ0EnA5o6R2RBf26s$ for graphic product... ATTN...WFO...ABQ...FGZ...GJT...SLC...VEF... ATTN...RFC...CBRFC...NWC... LAT...LON 37641081 37550979 37440914 37280885 36940875=20 36140890 35360912 34770937 34420966 34441000=20 34901043 35461101 35831207 36161337 36451369=20 37161356 37561334 37631191=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .