Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 01 2023 09:17:36 AWUS01 KWNH 010917 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-011345- Mesoscale Precipitation Discussion 1016 NWS Weather Prediction Center College Park MD 517 AM EDT Fri Sep 01 2023 Areas affected...northwestern AZ/southwestern UT/southeastern NV/eastern CA Concerning...Heavy rainfall...Flash flooding likely Valid 010914Z - 011345Z Summary...Areas of flash flooding are expected to continue in the short term with 1-2 inches of rain in 30-60 minutes but weakening of rainfall intensity will be possible after 12Z. The anticipated flash flood threat will extend from northwestern AZ into far eastern CA, southeastern NV and southwestern UT. Discussion...0845Z 10.3 micron imagery showed an MCS over northwestern AZ, with steady movement off toward the northwest and brightness temperatures of -70 to -80 C at times. Surface observations and local 88Ds showed thunderstorms continuing to develop with the leading edge of the MCS, along an outflow boundary translating north between 30-40 kt. Steep mid-level lapse rates of 7.5 to 8.5 C/km and advection of anomalous low to mid-level moisture from the south have maintained an axis of MUCAPE, ranging between ~500-1500 J/kg via the 08Z SPC mesoanalysis. Lingering instability was located over southern and western AZ, eastern CA into far southeastern NV/southwestern UT. These same locations of the southwestern U.S. were also beneath the right entrance region of a 70-90 kt upper level jet max, enhancing ascent through the column. While high dewpoint depressions at the surface were in place ahead of the MCS, helping to support strong to severe winds, highly efficient rainfall has been occurring with the leading edge of convection. Recent reports over the past few hours across central to northwestern AZ have recorded 1 to 2 inches of rain in ~30 minutes, followed by lighter rainfall afterward, and resulting in 2 hour rainfall totals of 1-3 inches in a few locations. The outflow boundary is expected to continue advancing toward the north over the next couple of hours, along with localized intense rainfall along its leading edge. Additional thunderstorm development remains possible from eastern San Bernardino County, CA into Clark and Lincoln counties in southeastern NV where convergent 850-700 mb flow was present within the western edges of the instability reservoir. Areas of flash flooding will remain likely over the next 1-3 hours, but as the outflow continues to surge north, stabilization in its wake may bring a temporary end to the flash flood threat. Uncertainty remains beyond 12Z and trends will be monitored for additional MPDs as needed. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-d0_QftwDQAWSCKASmC3XC1Ojr_k_p86I5KMZh9o5JUaUL5bk8rLLr_C0Id6btpkJyqb= N0MsaQGrAeh8sTdrYlTTAk0$ for graphic product... ATTN...WFO...FGZ...SLC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 38841216 38641184 38021166 37171204 36441225=20 35131190 34681233 34381299 34451344 34691396=20 34581443 34341522 34791570 36411536 37851444=20 38681307=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) .