Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jun 12 2023 19:02:56 AWUS01 KWNH 121902 FFGMPD IDZ000-NVZ000-CAZ000-ORZ000-130100- Mesoscale Precipitation Discussion 0471 NWS Weather Prediction Center College Park MD 302 PM EDT Mon Jun 12 2023 Areas affected...Sierra Nevada into the Great Basin Concerning...Heavy rainfall...Flash flooding possible Valid 121901Z - 130100Z Summary...Slow moving showers and isolated thunderstorms will expand in coverage through the afternoon around a mid-level trough centered across the Great Basin. This convection will move slowly, generally 5-10 kts, with rainfall rates in excess of 1"/hr likely. This could produce 1-2" of rainfall in a short period of time resulting in rapid runoff and possible flash flooding. Discussion...GOES-E visible imagery this afternoon shows mid-level cloud cover beginning to break within cyclonic flow around a mid-level trough centered over the Great Basin. As this cloud cover erodes, increasing instability noted by SPC RAP SBCAPE already rising to 250-500 J/kg is fueling initial Cu development, primarily along terrain features, from northeast NV through the Sierra Nevada. As the afternoon progresses, SBCAPE is progged to reach above 1000 J/kg which should drive rapid expansion and intensification of convection along this axis. This convection will form in an environment that will support rain rates that have a greater than 20% chance of reaching 1"/hr according to the HREF probabilities due to a favorable overlap of instability and PWs above +2 sigma according to the NAEFS ensemble tables. Although the convection through this evening will likely be scattered as shown by high-res simulated reflectivity, shortwaves embedded within the flow noted via the SPC RAP and within the GOES-E WV imagery could enhanced organization in a few areas, aided additionally by 0-6km bulk shear of 20-30 kts. 0-6km mean winds out of the E/NE could also drive some enhanced upslope into the Sierra Nevad to drive even more pronounced ascent for some heavier rain rates, and the HRRR sub-hourly fields indicate the potential for up to 0.5"/15 minutes. Not only will this convection contain these heavy rain rates, but individual cells will move slowly on 0-6km mean winds of just 5-10 kts and Corfidi vectors which collapse to just 5 kts at times, especially where convection becomes tied to the terrain. This could produce locally 1-2" of rain in some areas. This region has been saturated by 7-day rainfall that is more than 600% of normal in many areas, contributing to anomalous streamflows that are already high from ongoing snowmelt. This has resulted in FFG that is compromised to as low as 0.5"/1hr and 1-1.5"/3hrs, which has a 20-30% chance of exceedance according to the HREF. Where any of these slow moving storms occur, rapid runoff and flash flooding could result, but will be most likely over the sensitive terrain or any burn scars. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4Yh7rYh1oYrrtnoHXquGhiKJWpgNs-JrNokzMYDbIFFttu09_j8rsnkApysNitMv3u4v= KasmejIBiMJJR_2KyygNRnM$ for graphic product... ATTN...WFO...BOI...HNX...LKN...MFR...REV...STO...VEF... ATTN...RFC...CBRFC...CNRFC...NWRFC...NWC... LAT...LON 43001685 42831535 42361456 41801419 41431431=20 41261460 41091612 41091760 41001830 40771874=20 40251913 39451909 38341877 37461824 36901788=20 36351766 36091794 36151845 36371882 36741918=20 37241979 37832042 38382089 39372155 39992176=20 40882174 41882112 42711943 42971825=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) .