Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 10 2025 16:28:53 AWUS01 KWNH 101628 FFGMPD WAZ000-110300- Mesoscale Precipitation Discussion 1260 NWS Weather Prediction Center College Park MD 1128 AM EST Wed Dec 10 2025 Areas affected...Olympic and Cascade Ranges of Western Washington... Concerning...Heavy rainfall Valid 101630Z - 110300Z SUMMARY...Core of next atmospheric river surge through evening.=20 Rates of .33-.75"/hr based on elevation likely to further compound ongoing river flooding throughout the foothills of the Olympic and Cascade Ranges. Mud/Landslide potential continues to increase with amount of deep soil moisture. DISCUSSION...Recent regional RADAR mosaic shows core of solid stratiform rainfall is expanding across much of western Washington. CIRA LPW shows solid sub-tropical moisture connection tapping just northwest of Kaua'i only narrowing/concentrating along and south of the stationary front 42N/142W to the Olympic Range. RAP analysis and recent VWP network observations denote a surge of increased moisture/warm advection south of the front is directed orthogonally to the Olympic Range and further downstream to the western Washington Cascades with 30-40kts of boundary layer orographic ascent and Tds in the mid 50s. CIRA LPW also notes that core of enhanced 850-700mb remains well displaced (east over WA at this time) to the surface core indicative of the long, gentle upslope of the AR moisture plume; so with limited unstable air, orographic moisture flux convergence remains the primary driver of intense rates, so stark rainshadows and much lower rainfall totals/rates are expected in main, lower elevation valleys.=20=20 CIRA LPW analysis, extrapolation shows core of enhanced moisture below 700mb will continue to be directed toward the Juan de Fuca Strait/Northern Olympics into the Northern Washington Cascades over the next 6-9hrs supporting rates of .25" in the valleys to up to .75" in the highest terrain of the Cascades; and with the strong warm sub-tropic air, all but the most extreme peaks will continue to remain below the freezing levels. RAP/HRRR along with LPW extrapolation suggest core of enhanced moisture and winds will slowly reduce from supporting over 800 kg/m/s IVT values below 600 kg/m/s toward 00z with the front sagging south toward the mouth of the Columbia river by 06z.=20=20 FFG values are static in the Pacific Northwest and are not likely to be exceeded; however, NASA SPoRT shows 0-40cm saturation is near 90%, so nearly all those rates will be fully run-off. Flash flooding/rapid inundation flooding is not expected except for the highest reaches of watersheds/upper slope creeks, etc. but the rainfall will definitely continue a steady rise/expansion of ongoing river flooding across the area. Please refer to Northwest River Forecast Center and National Water Center products for details of these ongoing dangerous, life threatening conditions.=20 Additionally, deep layer saturation of the upper soils suggests mud/landslides may become increasingly possible through this evening, especially given affects of strong winds acting upon the trees and therefore their roots. Remain aware of this potential and refer to local emergency managers and USGS reports/products regarding landslide concerns. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8L2D4ky7YUPIc_XTauE7f5mOBTS_tFcGMz7lVQIdQ_QXNey033P0XO5k-9kianVdLxxG= MzntNDwJCMC7cWkTFvSaRJ0$ for graphic product... ATTN...WFO...OTX...PDT...SEW... ATTN...RFC...PTR...NWC... LAT...LON 49092147 48632099 48032072 47612090 46942137=20 46942189 47532210 47892184 48252199 48662228=20 49002260 48782323 47892312 47002346 47192395=20 47762440 48222461 48152365 48122326 49042328=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 3.28-Linux * Origin: Capitol City Online (1:2320/105) .