Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun May 21 2023 21:48:45 AWUS01 KWNH 212148 FFGMPD AZZ000-NVZ000-CAZ000-220345- Mesoscale Precipitation Discussion 0320 NWS Weather Prediction Center College Park MD 547 PM EDT Sun May 21 2023 Areas affected...portions of southern NV, western AZ, eastern CA/Sierra Nevada Concerning...Heavy rainfall...Flash flooding possible Valid 212146Z - 220345Z Summary...Slow moving thunderstorms will pose a localized flash flood risk across portions of the Desert Southwest into the Sierra Nevada through 03Z. Rainfall rates of 1-2 inches in 30-60 minutes are expected. Discussion...GOES West visible imagery showed widely scattered thunderstorms over the Southwest and into the Sierra Nevada with continued development of individual cells/clusters noted through 2130Z. Storms initiated off of the higher terrain with some advancing into lower elevations within an environment containing highly anomalous moisture. Standardized anomalies for precipitable water were +2 to +4 with values near 1 inch for parts of the Mohave Desert and 0.8 to 0.9 inches for the Colorado River Valley. While moisture was anomalous, it is only May and surface dewpoints were generally in the 40s with surface temperatures as of 21Z well into the 80s and 90s, promoting large inverted-V profiles on RAP analysis soundings across the region. High dewpoint depressions and weak MLCAPE of generally 500 J/kg or less were limiting factors to flash flooding, however, very weak mean steering flow of ~5 kt or less will support slow storm movement. Weak tropospheric flow will limit storm organization and duration over any given location with outflow generation promoting new storm development, but the moist environment may be enough to support brief but heavy rainfall rates of 1-2 inches in 30-60 minutes. With soil moisture and streamflows running higher than average in several locations, due in part to snowmelt in areas of terrain, flash flooding will be more likely with overlap of heavy rain. Coverage of any flash flooding is expected to remain isolated with 1.5-2.5 inches a general cap for storm totals. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7JsgYKfjuvYO1S4jIgOV3Zmdg6Qdk-qEaTxwI3-867t8rtPdivVnUKOqN4o4UTswW--T= kRYkwAfgEYZl8wOfclu5T_g$ for graphic product... ATTN...WFO...HNX...LOX...REV...SGX...STO...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 39011964 38511894 37481750 36861585 36351400=20 34681371 34211459 34111648 34761809 36521884=20 37741973 38812013=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) .