Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 02 2023 13:59:16 AWUS01 KWNH 021359 FFGMPD AZZ000-UTZ000-NVZ000-CAZ000-021900- Mesoscale Precipitation Discussion 0836 NWS Weather Prediction Center College Park MD 958 AM EDT Wed Aug 02 2023 Areas affected...Portions of the Great Basin Concerning...Heavy rainfall...Flash flooding possible Valid 021358Z - 021900Z Summary...Showers and thunderstorms will expand through the morning across the Great Basin. Rainfall rates may peak at 2"/hr, resulting in rainfall above 1" in some areas. Flash flooding is possible. Discussion...The GOES-E visible satellite imagery this morning shows rapidly bubbling Cu and TCu associated with deepening convection noted by increasing lightning strikes. Despite the early hour, this convection is blossoming downstream of a potent shortwave noted in the water vapor imagery driving local height falls, and within an area of modest upper diffluence as a jet streak subtly intensifies to the north. The 12Z U/A soundings at KVEF and KSLC measured PWs well above the 90th% and nearing daily records, driven by deep moist-adiabatic lapse rates and near record freezing levels suggesting efficient warm-rain processes today. This is combining with MUCAPE eclipsing 1000 J/kg to produce robust thermodynamics within which rain rates are already estimated via KESX to be 0.5-1"/hr, driving FLASH response as high as 300 cfs/smi. With convection rapidly bubbling this morning, the high-res is somewhat under-doing the current activity. Despite that, the guidance is quite aggressive expanding and intensifying thunderstorms through the early aftn. This is a likely evolution as the deep layer ascent overlaps increasingly extreme thermodynamics, resulting in rainfall rates which the HREF neighborhood probabilities suggest will exceed 1"/hr at times. Effective bulk shear is expected to slowly increase through the day to support modest organization, but in general the environment will support primarily pulse convection with short temporal lifespans. However, storm mergers and outflow collisions could result in briefly heavier rain rates, with the recent HRRR suggesting locally 0.5"/15 minutes. Storm motions will remain generally slow as shown by 0-6km mean wind vectors, and this mean flow aligned to weak Corfidi vectors suggests short term training to the north is likely. Where this occurs, event total rainfall of 1-2" is possible as reflected by HREF probabilities. 7-day rainfall from southern NV through northwest AZ and into the Slot Canyon region of UT has been well above normal according to AHPS, resulting in compromised FFG of 0.5-0.75"1/hr and 1-1.5"/3hrs. The HREF exceedance probabilities are modest at 10-20% for these thresholds, but the rainfall needed to produce runoff/flash flooding is likely even lower across sensitive burn scars, slot canyons, urban areas, and dry washes. Where any of these slow moving storms pulse up atop these more vulnerable areas, instances of flash flooding could occur. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6Ln4OWw4RawFR7u7qofWnH3MOqpYt8tSwb2_NtxED5Cw8g_LX3A8LBlcxr8q2pisQLKF= awlyOoAG_Rix68R-EdqM41c$ for graphic product... ATTN...WFO...FGZ...LKN...SLC...VEF... ATTN...RFC...CBRFC...CNRFC...NWC... LAT...LON 40451470 40441378 40091273 39441169 38401113=20 37691136 37031192 36371285 35511366 34971471=20 34721542 34951601 35881631 37571638 38971602=20 =20=20=20=20=20=20=20=20=20=20=20=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) .