Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Aug 02 2023 18:18:21 AWUS01 KWNH 021818 FFGMPD WYZ000-AZZ000-UTZ000-NVZ000-030000- Mesoscale Precipitation Discussion 0837 NWS Weather Prediction Center College Park MD 217 PM EDT Wed Aug 02 2023 Areas affected...Northern Arizona, Southern and Central Utah Concerning...Heavy rainfall...Flash flooding likely Valid 021816Z - 030000Z Summary...Showers and thunderstorms will increase across northern Arizona and much of Utah through the evening. Rainfall rates may at times reach 2"/hr, which through training could produce locally 1-3" of rain. Flash flooding is likely. Discussion...The GOES-W visible imagery this aftn shows expanding agitated Cu blossoming downstream of a potent shortwave lifting out of southern Nevada. This shortwave is rotating northward around the periphery of a mid-level ridge centered over the Southern Plains, and working in tandem with upper diffluence within the tail of a modest jet streak to drive deep layer ascent. This synoptic lift is occurring atop extremely favorable thermodynamics characterized by PWs that are above the 90th percentile and near daily records (1.25-1.5 inches) overlapped with SBCAPE increasing above 1500 J/kg in ample clearing over Utah. The result of this evolution is the increasing convective coverage, with intensity ramping up as well noted by radar-estimated rain rates exceeding 1"/hr via KICX WSR-88D. As the potent vorticity max continues to lift north/northeast, it will drive enhanced ascent into even more robust thermodynamics due to SBCAPE climbing above 2000 J/kg. This setup will likely result in widespread convective coverage, and this morning's high-res guidance has become even more impressive with both coverage and intensity from northern Arizona through much of Utah. The recent HREF neighborhood probabilities suggest rain rates exceeding 1"/hr will become increasingly widespread, resulting in sub-hourly rainfall as high as 0.75" according to the UA WRF and HRRR sub-hourly fields. Generally S/SW flow through the lower half of the column observed in 12Z U/A soundings will support storms that will move N/NE at around 15-20 kts, but aligned Corfidi vectors at around 10 kts will support at least short term training of these rates. Additionally, increasing effective bulk shear rising to 25-30 kts should help organize cells into clusters, additionally enhancing the intensity and duration of rainfall at times. Through this evolution, the HREF suggests rainfall could reach as high as 3". which is supported as well by the experimental RRFS TL ensemble LPMM showing pockets of 2+" of rain. During the last 7 days, rainfall has been generally 150-300% of normal across far northern AZ into the southern half of UT as shown via AHPS. This has lowered FFG and resulted in USGS streamflow anomalies that in some places are well above normal. Additionally, this area has some extremely sensitive terrain features such as usually dry washes, slot canyons, and burn scars, which are even more vulnerable to heavy rain rates. This suggests that any training of intense rates could result in flash flooding, but it is most likely to occur over these more sensitive features. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_ED05rPT5U3J0uQgEFdzWWPaIjkmf8QzQYHm5vmww-ncCDDxexIqPDuplZiqV1Dp0czV= OLzxtVbGFIp3TnZdylWPdqE$ for graphic product... ATTN...WFO...FGZ...GJT...RIW...SLC...VEF... ATTN...RFC...CBRFC...NWC... LAT...LON 41081033 41080948 40630943 40230969 39101017=20 37911021 36801055 36111098 35671187 35601250=20 35571325 35861385 37251414 38821380 39851341=20 40571249 40941172=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) .