Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 20 2023 22:56:51 AWUS01 KWNH 202256 FFGMPD MTZ000-IDZ000-210455- Mesoscale Precipitation Discussion 0954 NWS Weather Prediction Center College Park MD 655 PM EDT Sun Aug 20 2023 Areas affected...Southwest to Central ID...Far Southwest MT Concerning...Heavy rainfall...Flash flooding possible Valid 202255Z - 210455Z SUMMARY...Rainfall associated with Tropical Storm Hilary's deep moisture plume will tend to increase in intensity going through the late afternoon and evening hours. Areas of flooding and potentially some instances of flash flooding will be possible. DISCUSSION...The latest GOES-W satellite imagery shows a very impressive poleward advance of deep moisture associated with Tropical Story Hilary extending across the Great Basin and well up across the northern Rockies. Radar and surface observations show a widespread axis of moderate to locally heavy rain impacting these areas with some of the more concentrated rains impacting portions of the Snake River Valley and up across the higher terrain of the Sawtooth Range and adjacent Bitterroot Mountains. SBCAPE values of 500 to 1000 J/kg are seen situated over much of the Snake River Valley where there has been enough filtered solar insolation despite the clouds and rain to help yield a bit of boundary layer heating. The uptick in instability has been leading the way for some locally heavier shower activity to develop within the broader stratiform rainfall shield across the western part of the Snake River Valley over the last 1 to 2 hours. A combination of strengthening 700 mb south to southwest warm air advection and moisture flux ahead of the track of Tropical Storm Hilary into the Southwest U.S. and strong right-entrance region upper-level jet dynamics should maintain an elongated shield of moderate to heavy rain across areas of southwest to central ID and into far southwest MT where enhanced upslope flow will be noted as well. Locally strong orographic forcing in conjunction with the synoptic scale pattern should yield some efficient rainfall processes with warm rain considerations for increasing rainfall rates heading through the evening hours. As also suggested by the 18Z HREF guidance, expect some rainfall rates to gradually reach or exceed a 0.50" per hour, with the potential for some isolated rates of 0.75" to 1" per hour with some occasionally embedded convective elements. Some additional storm total amounts of 2+ inches will be possible by late evening where these heavier rates persist. Given the persistent rainfall axis and concerns over increasing rates this evening, some areas of flooding and isolated instances of flash flooding will be possible. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!90S7eUck96_N4Rdd7ogh_OoMZg7MmrNkEIqpBJ3SdbKvahMyDWXZ5sLR6AzCAvnZ7z4O= IdxgSzV77-FVhKoFyCICe28$ for graphic product... ATTN...WFO...BOI...MSO...PIH...TFX... ATTN...RFC...MBRFC...NWRFC...NWC... LAT...LON 45381341 45221246 44731194 43761217 42981322=20 42431453 42241613 42551677 43141690 43721642=20 44381522 45111440=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) .