Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 22 2023 18:25:36 AWUS01 KWNH 221825 FFGMPD WYZ000-AZZ000-UTZ000-IDZ000-230020- Mesoscale Precipitation Discussion 0962 NWS Weather Prediction Center College Park MD 224 PM EDT Tue Aug 22 2023 Areas affected...northwestern AZ, UT into western WY Concerning...Heavy rainfall...Flash flooding possible Valid 221822Z - 230020Z SUMMARY...The expected development of thunderstorms during the afternoon will increase the threat for flash flooding from portions of northwestern AZ into central UT and far southwestern WY. Rainfall rates of 1-2 inches in an hour or less are expected with the stronger storms that develop. DISCUSSION...Water vapor and layered PW imagery at 18Z showed UT=20 beneath deep-layered moisture sandwiched between upper troughing over the West Coast and a large ridge over the central U.S. The 12Z sounding from SLC showed relatively high relative humidity throughout the column with a PW value of 1.09 inches, between 2 to 3 standard deviations above the mean. Flow was unidirectional from the south with sufficient speed shear for at least some organization of thunderstorms. Eastern portions of the Great Basin were also located within the right entrance region of a 70-80 kt jet max centered near 300 mb via GOES West DMVs, favoring ascent through divergence aloft. One missing ingredient for robust thunderstorm development is instability with a fair amount of cloud cover in place west of the Wasatch Mountains and the 18Z SPC mesoanalysis indicating MLCAPE was generally less than 500 J/kg north of the AZ/UT border. However, visible satellite imagery showed partly cloudy to mostly clear skies along and east of the Wasatch Range along with isolated thunderstorms over the past few hours over the higher terrain. Continued solar heating within areas of reduced cloud cover, from northwestern AZ into central UT...focused around the Wasatch...and far southwestern WY is expected to increase MLCAPE into the 500-1000 J/kg range by 21Z. Thunderstorms are expected to develop by 21Z as low level inhibition is overcome with increasing coverage of thunderstorms into the early evening. The environment is expected to support rainfall rates of 1 to 2 inches in an hour or less with some S to N or SW to NE training/repeating segments, which could generate some areas of flash flooding. Flash flood potential will be greatest where overlap of heavy rain occurs with vulnerable slot canyons and dry washes. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5AvaM0Co--Oj8ohqTBQ-1xESzaNuhJDExdDeN95484LxqTM0anIPmjp7ASkllH1JG_WG= 7tWyLzpuYyyiIhZAJBFxN14$ for graphic product... ATTN...WFO...FGZ...PIH...RIW...SLC...VEF... ATTN...RFC...CBRFC...NWRFC...NWC... LAT...LON 42571069 42351019 41551032 40611000 39341029=20 37201120 36371160 35561201 35461278 35841331=20 36291352 37051358 37961340 39171308 40691241=20 42131143=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .