Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 22 2024 19:02:55 AWUS01 KWNH 221902 FFGMPD AZZ000-UTZ000-NVZ000-230100- Mesoscale Precipitation Discussion 0920 NWS Weather Prediction Center College Park MD 302 PM EDT Thu Aug 22 2024 Areas affected...northern Arizona, southern Utah Concerning...Heavy rainfall...Flash flooding possible Valid 221915Z - 230100Z Summary...Showers and thunderstorms will continue to expand across northern Arizona and lift northward through the afternoon. Rainfall rates of 1-2"/hr are likely, which could produce rainfall accumulations above 0.5"/15 minutes in some areas. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows a rapid increase in convective coverage from the western Mogollon Rim across much of NW AZ and into far SW UT. This convection is building in response to destabilization noted by MLCAPE that has climbed around 600 J/kg the past 3 hours to as high as 2000 J/kg, combined with PWs of 1-1.3 inches. Into these impressive thermodynamics, forcing for ascent is increasing downstream of a longwave trough positioned over the Pacific Coast, as height falls, a strengthening jet streak aloft, and weak impulses embedded within the flow combine into the eastern Great Basin and Four Corners. Recent rainfall rates have been estimated as high as 1-1.5"/hr within fresh convection, and although coverage so far has been modest, an expansion of lightning cast probabilities above 50% suggest coverage should rapidly expand in the next 1-2 hours. The high-res CAMs including the recent runs of the HRRR, ARW2, and UA WRF suggest convection will rapidly expand the next few hours across northern AZ and pivot slowly into southern UT. Storm organization is likely within this region as 0-6km bulk shear persists at 25-35 kts, producing clusters of multicells, and even isolated supercells, in the area. This could locally enhance rain rates, and while the HREF neighborhood probabilities for 1"/hr peak around 25%, the HRRR sub-hourly rainfall accumulations indicate rates could briefly approach 3"/hr, most likely in any organized clusters, producing 0.5 to 0.75 inches of rain in just 15 minutes. These storms will tend to lift north/northeast on 0-6km mean winds of around 20 kts, but Corfidi vectors fall to around 10 kts over AZ while remaining parallel to the mean wind, suggesting some backbuilding/training of cells. The intense rain rates will be most problematic across sensitive terrain features such as slot canyons, burn scars, and dry washes, which are prevalent in this area, but 0-40cm soil moisture as measured by NASA SPoRT is also above the 80th% in many areas suggesting vulnerable soils anywhere in the region. Where training occurs, locally as much as 2-3" of rain could occur, additionally enhancing the potential for flash flooding through the evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4D6v_foAaayeOGgL1WbpLhnuLcS06AiIRZxwxXMyNCBTIl03GSl5XI2MvO1pLeUml4-X= 2KZta_Su3qMR0VzJUEUDLKQ$ for graphic product... ATTN...WFO...FGZ...GJT...SLC...VEF... ATTN...RFC...CBRFC...NWC... LAT...LON 38861098 38411039 37751069 37131083 36081102=20 35541147 35301166 35021207 35021253 35051274=20 35291349 35891435 36261464 37531438 38321334=20 38811219=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) .