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   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   
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