Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jun 13 2023 18:29:17 AWUS01 KWNH 131829 FFGMPD MTZ000-WYZ000-IDZ000-ORZ000-140000- Mesoscale Precipitation Discussion 0478 NWS Weather Prediction Center College Park MD 228 PM EDT Tue Jun 13 2023 Areas affected...Idaho, southwest Montana, northwest Wyoming Concerning...Heavy rainfall...Flash flooding possible Valid 131827Z - 140000Z Summary...Slow moving showers and thunderstorms will increase across the region this aftn. Rainfall rates of 1"/hr are likely at times, which could produce locally as much as 3 inches of rain. This will lead to rapid runoff which could produce isolated instances of flash flooding. Discussion...Mid-level cloud cover is beginning to erode as noted on the GOES-E visible imagery, which is allowing for rapid Cu development within mid-level clearings. Some of this Cu is becoming deep enough to manifest as showers and even isolated thunderstorms across the area as SPC RAP SBCAPE climbs to 1000-1500 J/kg. At the same time, a shortwave clearly evident in the WV imagery in southwest MT will lift slowly north and provide additional ascent in its vicinity, while a larger scale trough approaches from British Columbia to drive modest height falls. Together these will drive sufficient deep layer ascent for another day of widespread showers and thunderstorms as the rich thermodynamic environment persists with 1000-2000 J/kg of SBCAPE and PWs of 0.75 to 1 inch. As the aftn progresses and surface heating intensifies, the high-res guidance is in good agreement that showers and thunderstorms will develop across most of the area as the weak convective lid noted on the 12Z U/A soundings from KTFX and KOTX gets broken. Weak mid-level lapse rates through a moistening column will support moist updrafts to create efficient rain rates which the HREF indicates could exceed 1"/hr at times, while the HRRR sub-hourly accumulations reach as high as 0.25-0.5 inches in 15 minutes. The activity will likely be diurnally forced so will wane with loss of heating this evening, but increasing ascent occurring during the overlap of highest PW/instability will result in widespread convection during the aftn/eve. Although the convection will generally be the pulse variety due to limited shear, individual cells will move very slowly at around just 5 kts as reflected by 0-6 km mean winds. This will allow these heavy rates to produce 1-2" of rainfall in isolated locations. This region has been wet recently as analyzed by 7-day AHPS rainfall that is 300-600% of normal leading to FFG that is as low as 0.5"/1hr, for which the HREF exceedance probabilities reach as high as 60%. This indicates that while runoff across sensitive terrain and wet soils is likely, some of this could result in isolated instances of flash flooding as well. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8byApV6q3kPjA-Dy0HMVMQNrAkg2dkY76nqfBH_J-iWilxLFb0G-FdMhpYSGOVT_EQrG= jsEjWHMOTBXzVPDuQZo8rSw$ for graphic product... ATTN...WFO...BOI...BYZ...MSO...OTX...PDT...PIH...RIW...TFX... ATTN...RFC...CBRFC...MBRFC...NWRFC...NWC... LAT...LON 46551325 46231139 45841013 45170935 44250902=20 43420894 42600910 42180983 42101119 42261293=20 42721452 43561601 44721682 45541680 46071656=20 46421546=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) .