Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 07 2025 06:15:12 AWUS01 KWNH 070615 FFGMPD WAZ000-071000- Mesoscale Precipitation Discussion 1057 NWS Weather Prediction Center College Park MD 214 AM EDT Sun Sep 07 2025 Areas affected...western/central Washington State Concerning...Heavy rainfall...Flash flooding possible Valid 070614Z - 071000Z Summary...An instance or two of flash flooding is possible across the Pacific Northwest as scattered thunderstorms move slowly/erratically over the next 2-4 hours. Areas of 1 inch/hr rain rates are expected. Discussion...Recent radar mosaic imagery depicts a gradual expansion in convective coverage across western and central Washington State currently. The storms are generally moving northwestward, though weak low-level shear was promoting areas of outflow-driven activity with erratic storm motions. Spots of 1 inch/hr rain rates were being estimated per MRMS with the more dominant activity, suggesting that flash flooding might occur especially if that rainfall occurs atop sensitive ground conditions and/or burn scars. The storms are being supporting by 1) ascent lifting northward around the base of a larger-scale mid/upper trough over the northeastern Pacific, 2) steep mid-level lapse rates (generally above 7C/km away from storms), and 3) a moisture plume across the area, with PW values generally in the 1-1.3 inch range. Each of these factors suggest that an instance or two of flash flooding might occur as storms move through the region in the near term. Models/observations suggest the period of peak flash flood risk might only extend through 09Z/2a PDT or so. The mid-level vorticity max helping to force ongoing convection should lift northward into southwestern Canada, resulting in a minimum in forcing aloft amid stabilizing low-levels from widespread rainfall. A limited threat for thunderstorms may exist beyond the 09Z/2a PDT timeframe, and flash flood potential will be reassessed around that time. Of note - some of the thunderstorms may also produce dry lightning and fire starts. Additional information on these threats can be found at your respective local forecast office (weather.gov) and SPC fire weather information (spc.noaa.gov). Cook ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6-2GaFK6ln1qD0eK1_sxoe7WzmHRV_M3Au8Pv9bCEzSu2e0My9vEYfPd9g1SNhEkeD76= k6qOHzI6tSmoI5XNYTh_tiI$ for graphic product... ATTN...WFO...OTX...PDT...PQR...SEW... ATTN...RFC...PTR...NWC... LAT...LON 48712153 48411990 47381918 46222023 46612342=20 47952347 48372269=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .