Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 01 2023 21:06:15 AWUS01 KWNH 012106 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-020300- Mesoscale Precipitation Discussion 1020 NWS Weather Prediction Center College Park MD 505 PM EDT Fri Sep 01 2023 Areas affected...Portions of the Great Basin Concerning...Heavy rainfall...Flash flooding likely Valid 012104Z - 020300Z Summary...Showers and thunderstorms will increase in coverage and intensify through this evening. These storms will lift northward and train, with 1+"/hr rain rates resulting in axes of 2-3" of rainfall. Flash flooding is likely. Discussion...The regional radar mosaic this afternoon indicates widespread showers and thunderstorms developing across the low deserts of CA and into southern AZ, with additional thunderstorms blossoming near Las Vegas, NV. These storms are being pulled northward within nearly unidirectional flow between an anomalous upper low digging across CA evident on WV imagery, and a retreating but expansive ridge of high pressure to the east. Southerly flow between these two features is being pinched, driving anomalous moisture transport northward noted by PWs measured by GPS reaching 1.8 inches, as high as +3 standard deviations, extending into eastern NV. This is combining with SBCAPE of 1000-2000 J/kg to provide an extremely favorable environment for convection with heavy rain. Additionally, weak shortwaves embedded within the flow are lifting northward to provide additional ascent, which when combined with effective bulk shear of 25-35 kts will result in clusters of organized thunderstorms continuing through the evening. Rainfall rates as estimated by local radars have been 1-1.5"/hr in many cells, and these rates are likely to continue as reflected by HREF neighborhood probabilities for 1+"/hr peaking above 50% by 02Z, coincident with the UA WRF hourly precipitation showing widespread areas of 0.75" or higher. This is also reflected by the HRRR sub-hourly fields indicating 15-min rainfall that may reach 0.5". The continued northerly flow is progged to drive PW anomalies above +3 sigma as far as 40N this evening according to the SREF, which further supports the high-res simulated reflectivity expanding convection much farther north through the evening. With mean 0-6km winds of around 20 kts aligned to the Corfidi vectors, it is likely these showers and thunderstorms will train in many areas, resulting in the HREF exceedance probabilities for 3"/6hrs as high as 40%. 14-day rainfall across the Great Basin has been generally above 300% of normal, and USGS streamflow anomalies are well above the 90th percentile in many areas. This has led to compromised FFG which could quickly be overwhelmed by these intense rates despite the generally progressive cells. Flash flood warnings are already in effect in some areas, and additional instances of flash flooding, with even more expansive coverage, is likely as convection lifts northward during the next several hours. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-Bl6b03A-qCOsSNCz4fJ9yMHtXzB-Wtd7MbH4KS4YDrSACMc0jEXF3qUekWT1xsoH_J3= epg6FRc-u4YVuxKvODyCWzI$ for graphic product... ATTN...WFO...LKN...SLC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 40641504 40621388 40141345 38871323 38221322=20 36921329 36151354 35321414 35141466 35091527=20 35111581 35321647 35841729 37481749 39061682=20 40271583=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) .