Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 02 2024 18:45:09 AWUS01 KWNH 021845 FFGMPD ORZ000-WAZ000-030630- Mesoscale Precipitation Discussion 0375 NWS Weather Prediction Center College Park MD 244 PM EDT Sun Jun 02 2024 Areas affected...Much Western Oregon and Western Washington Concerning...Heavy rainfall Valid 021843Z - 030630Z SUMMARY...A potent, late-season atmospheric river will bring locally heavy and prolonged moderate rainfall to much of Pacific Northwest with a focus south from the Seattle metro area through western Oregon into tonight. Flooding of creeks and streams and in urban areas are possible. DISCUSSION...An atmospheric river (AR) with connections across the Pacific to Southeast Asia will continue to push into the Pacific Northwest into the overnight tonight before tapering off as it shifts south early Monday. Precipitable water (PW) values of 1.5" have reached the south-central Oregon coast as of 18Z per GPS sensors and guidance suggests it may reach 1.7" this afternoon which is 3 to 4 standard deviations above normal. Vertically integrated water vapor transport (IVT) exceeds 800 kg/ms in guidance which is notable for such a late season event. Low level flow in this AR is generally WSWly at 40-50kt. Prolonged hours with topographically enhanced rainfall of 0.25" to 0.5" are likely this afternoon and evening over much of the coastal and Cascade terrain of southwest WA and northwest OR per 12Z HREF guidance before shifting south over southwest OR into CA and weakening overnight. HREF probability-matched means (a reasonable worst case scenario) for 6hr QPF are 1-3" for Coastal Ranges and Cascades in southwest WA and the northern half of western Oregon 18-00Z and then over much of the terrain in western Oregon for the 00Z-06Z with a local PMM for 24hr QPF of 2-5" for much of the Pacific Northwest terrain ending 12Z Monday. Urban areas south of Seattle and including Portland are generally forecast to receive up to 1.5", though localized convective elements may result in more over lower terrain/urban areas. Rain rates such as these in terrain are likely to cause significant rises in main-stem rivers, though drier antecedent conditions should preclude main-stem flooding. However, flooding of creeks and streams as well as urban areas are possible. Snow levels are anticipated to rise to 8000-10,000ft in the core of the AR this afternoon which will promote snowpack melting and may further exacerbate localized flooding concerns. Jackson ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8K-7MoeFeL8EA29-4DekNbcivOpwIyRkUb56zbYSOKhfjZillL9OsDXAQF66dcwkctEk= nbhQ6ZzSTB9aGxf7NRJBTZU$ for graphic product... ATTN...WFO...MFR...OTX...PDT...PQR...SEW... ATTN...RFC...CNRFC...NWRFC...NWC... LAT...LON 47972120 47722085 45932150 45112155 44382170=20 43832179 43182203 42512222 42772291 42832362=20 42272392 42322449 43182477 45402432 47372447=20 47742372 47382298 47902178=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .