Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 03 2023 18:03:09 AWUS01 KWNH 031803 FFGMPD MTZ000-WYZ000-UTZ000-IDZ000-040000- Mesoscale Precipitation Discussion 0848 NWS Weather Prediction Center College Park MD 202 PM EDT Thu Aug 03 2023 Areas affected...eastern ID, northern UT, western/central WY Concerning...Heavy rainfall...Flash flooding possible Valid 031801Z - 040000Z Summary...Showers and thunderstorms will increase in coverage through the afternoon ahead of an upper level low. Rainfall rates will intensify to 1-2"/hr at times, resulting in rain accumulations of 1-2" with locally higher amounts. Flash flooding is possible. Discussion...The GOES-W visible satellite imagery this aftn shows expansive cloud cover across northern UT and into eastern ID around a pronounced upper level low spinning north of Salt Lake City, UT. To the east of the denser clouds, breaks/clearing has allowed SBCAPE to climb to above 1000 J/kg according to the SPC RAP analysis, resulting in rapid Cu growth during the past hour. Additional ascent is being provided by height falls just downstream of the upper low, and within modest upper diffluence within the tail of an upper level jet streak positioned just north of the area. The deeper Cu is already producing scattered showers with radar-estimated rain rates of around 0.5"/hr. These will likely continue to increase as record PWs, which were measured via 12Z U/A soundings of 1.22 inches at SLC and 1.05 inches at RIW, continue to increase on persistent southerly moist advection. The overlap of deep layer ascent and the impressive thermodynamics will result in an expansion and intensification of convection through the aftn. This is reflected by widespread coverage of cells in the high-res simulated reflectivity, with rain rates likely reaching 1-2"/hr as reflected by increasing HREF neighborhood probabilities. The HRRR even suggests 15-min rainfall could reach as high as 0.75" in isolated locations, meaning brief 3"/hr rates are possible. This will occur despite minimal effective bulk shear driving primarily short-duration pulse storms. However, extremely slow storm motions on 0-6km mean winds of just 5 kts within this pulse environment will allow for a temporal extension of heavy rainfall at times, with storm mergers and outflow collisions driving additional development and brief even more intense convection. Where any storms can redevelop through interaction or pulse up more impressively, rainfall could reach 1-2", with locally higher amounts possible as shown by HREF neighborhood probabilities for 3 inches. This area is vulnerable to runoff due to FFG that has been compromised from 14-day rainfall that is generally 150-300% of normal. This has produced USGS streamflow anomalies that are primarily above normal, suggesting the soils are mostly hydrophobic, and could be quickly overwhelmed by any slow moving heavy rain producing cell. Sensitive terrain, burn scars, and urban areas will be most susceptible to runoff this aftn, but instances of flash flooding are possible anywhere a slow moving storm can occur. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-oJV2no8krMRmBXnHJ5UAc6THUCZTXTdXjx5YTAVZrxN4VxjhEOHvoOXDjvKFgvhHifx= sVNSaQ0O2aueXxxXLenL1J4$ for graphic product... ATTN...WFO...CYS...PIH...RIW...SLC...TFX... ATTN...RFC...CBRFC...MBRFC...NWRFC...NWC... LAT...LON 44851093 44840962 44340890 43660818 42690718=20 41590678 41280728 41010876 41081142 41271247=20 41521301 42011344 43131355 44171265 44731146=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) .