Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 02 2023 19:24:02 AWUS01 KWNH 021923 FFGMPD AZZ000-CAZ000-030000- Mesoscale Precipitation Discussion 1026 NWS Weather Prediction Center College Park MD 323 PM EDT Sat Sep 02 2023 Areas affected...Deserts of CA and southwest AZ Concerning...Heavy rainfall...Flash flooding likely Valid 021922Z - 030000Z Summary...Showers and thunderstorms will increase through the afternoon. Rainfall rates will likely reach 1-2"/hr at times, resulting in pockets of 2-3" of rainfall. Flash flooding is likely. Discussion...The regional radar mosaic this afternoon shows rapidly increasing coverage of convection from the Mexico/CA border northward into the high deserts and across far southwest AZ. This convection is blossoming beneath an impressive shortwave noted on the GOES-W WV imagery lifting slowly northward from Yuma, AZ, with additional ascent provided through the broad right-rear tail of a jet streak crossing the western Great Basin. Thermodynamics across the area are supportive of heavy rain, with PWs measured by GPS of 1.75-2 inches, collocated with SBCAPE as high as 3000 J/kg. Nearly unidirectional S/SW flow through the low/mid part of the column evident in morning U/A soundings is helping to advect these robust thermodynamics northward, supporting the rainfall rates currently estimated by local radars reaching 1.5"/hr. The high-res guidance is not handling the coverage of current activity very well, so confidence in evolution is a bit lower than normal. However, the extremely impressive PWs/instability in the vicinity of the potent shortwave should continue to drive an increase in both coverage and intensity of thunderstorms until the shortwave lifts farther north later today. While the models are under-doing the coverage, the cells progged by simulated reflectivity in the high res do show an increase in intensity, and rainfall rates noted by the HREF could reach 2"/hr or more, with HRRR sub-hourly precip depicting isolated 0.75"/15 min potential. While the mean storm motions are likely to remain progressive to the north at around 20 kts, using the 0-6km mean wind as proxy, strongly veered Corfidi vectors collapsed to just 5-10 kts indicate the potential for some backbuilding into the greater instability/moisture leading to training. Where this occurs, axes of rainfall approaching 3" is possible as progged by HREF 3"/6hr neighborhood probabilities. Much of this region has experienced well above normal rainfall recently, with 24-hr rainfall from MRMS as much as 2-4" contributing to 7-day rainfall from AHPS that is almost uniformly 300-600% of normal. This has compromised soils to be even more vulnerable than typical, so it is likely any of the more intense rain rates will lead to instances of flash flooding the next several hours. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8UDISCuEgPZI51ENzhmqtMxBMm0NNKPamsThzyB3j-1lw_CDR2J2fHdJf1hYBr4hwjFU= NtIqwdsNCe31R_TN2X-AanQ$ for graphic product... ATTN...WFO...FGZ...PSR...SGX...TWC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 35311621 34901493 34551393 34371322 34011259=20 33581236 32771230 31921242 31771295 31981357=20 32251427 32381484 32561546 32801610 33111644=20 33661670 34181687 34771701 35291686=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) .