Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 27 2023 18:50:36 AWUS01 KWNH 271850 FFGMPD MTZ000-WYZ000-IDZ000-ORZ000-WAZ000-280050- Mesoscale Precipitation Discussion 0596 NWS Weather Prediction Center College Park MD 249 PM EDT Tue Jun 27 2023 Areas affected...Northern Rockies Concerning...Heavy rainfall...Flash flooding possible Valid 271850Z - 280050Z SUMMARY...Thunderstorms dawdling across the Northern Rockies will contain heavy downpours and could result in flash flooding, especially in areas with sensitive soils and along rugged terrain. DISCUSSION...An upper low positioned southeast of the Blue Mountains of northeast Oregon is working in tandem with a broad upper trough over the Great Basin and southern CA to generate healthy upper level divergence over the Northern Rockies. PWATs across the region are around 0.75" for most of the region. PWATs will be around the 90th climatological percentile this afternoon and early evening. RAP forecasts show >500 J/kg of MLCAPE will be present in western MT and north-central ID, with the rest of the highlighted region ranging between 250-500 J/kg. One of the primary factors supporting a flash flood threat are mean cloud layer wind speeds that are weaker than 5 knots in some areas. There is very little in the way of vertical wind shear present, so aside from surface based heating, any residual outflows produced by early onset thunderstorms may help to ignite additional storms this afternoon. These slow moving storms producing torrential downpours could result in as heavy as 1.5"/hr rainfall rates, which would be at or above most of the region's current 1-hr FFGs. RAP forecast soundings in north-central ID this afternoon showed low-mid level RH values around 90%. The 12Z HREF did depict 6-hr QPF > 10-yr ARI probabilities as high as 40-45% between 18-00Z this afternoon too. The region also still features unusually saturated soils with 14-day rainfall totals, according to AHPS, that were as high as 200-300% of normal central ID and south-central MT. Given the potential high end rainfall rates mentioned above, as well as the saturated soils in the region, it is possible flash flooding for occur in these areas, as well as in rugged terrain and poor drainage areas. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5bup-zzo2-DHSrCfKSd-2p07lQB8cxGpckPTV5Ohd6D8LAKgcTiMuDHyGkkS4gEgP6ZR= -HFwKpAlxzUGjdjKAZKHOBk$ for graphic product... ATTN...WFO...BOI...BYZ...MSO...OTX...PDT...RIW...TFX... ATTN...RFC...MBRFC...NWRFC...NWC... LAT...LON 47681350 46961188 47151045 47210990 46950930=20 45700949 44700894 44180886 43760909 44410996=20 44831093 45081219 44981407 44941544 44641702=20 45271764 45931746 46281659 46701570 46891500=20 47111439=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) .