Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 25 2024 17:03:35 AWUS01 KWNH 251703 FFGMPD ORZ000-WAZ000-260300- Mesoscale Precipitation Discussion 1189 NWS Weather Prediction Center College Park MD 1202 PM EST Wed Dec 25 2024 Areas affected...Western WA...Western OR... Concerning...Heavy rainfall Valid 251700Z - 260300Z SUMMARY...Strong deepening dynamics will back winds toward more favorable orographic ascent by 19-20z and increase rainfall efficiency to near .5"/hr in favored spots by 00-03z. Runoff will likely increase stream flows, but flooding is not expected quite yet except for the most vulnerable/traditional locations. DISCUSSION...GOES-W WV suite shows a compact shortwave crossing the Southeast Gulf of AK at the far southeast edge of the global scale trof that has been dominating the Bering Sea. The compact wave as a solid negative tilt to it associated with a broad strong polar Pacific Jet with a 150-170kt 250mb streak supporting solid low level strengthening wind profile with a strong warm front starting to press eastward with 700-500mb moisture flux & WAA resulting in lighter showers across W WA and NW OR at this time.=20 Low level winds continue to strengthen with 40-50kts at 850-700mb per LGX VWP but remaining mainly parallel to the coast, but increasing reflectivity and polar microwave passes suggest warm front is approaching quickly and will veer the wind profile toward 21z across W WA and W OR. This will be accompanied by the core of the sub-tropical moisture stream; with leading 850-700mb moisture advected on 60-70kts of flow with IVT values increasing from 400 kg/m/s toward 600 kg/m/s. Upslope component on the SW facing Olympics and Willapa Hills will see first brunt with .33" increasing to near, occasionally reaching .5"/hr rates by 00z=20 when winds start to peak near 80kts from the SW and IVT peaks near 850-900 kg/m/s. Rainfall totals of 1.5-2.5" by 03z, are likely to fully saturate the remaining capacity of the upper soils.=20 Currently, much of the area is about 70-80% capacity through 40cm and while a lot, this is above average in the 70th percentile near the coast but increasing toward 75-80th percentile in the higher elevations and further inland. As a result, increased run-off will be channeled to the streams; and while this is a strong AR, the duration is not expected to be long to result in any sizable flooding but increase stream flows in preparation for subsequent AR surges over the following days. As the front passes winds will slacken and veer to more due west and much of NW WA will be out of the core of the AR moisture plume with .5-.75" PWATs...while shifting into W OR with 1 to nearing 1.25" total PWats. This will maintain stronger rates in the coastal range of W OR for a few more hours before the next wave/lifts northward later on Thursday morning. Still by 03z, west facing orography in NW OR will experience 1-2.5" of rain even to the tops of the peaks, while .5-1" totals are expected in the lower valleys (less than .25" in traditional shadowed locations.=20 Similarly, a good soaking and setting the stage for a likely active pattern of AR pulses though the weekend; however flooding is not likely to be an issue with exception of the most susceptible/traditionally flooded areas.=20=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!63vZsNSo0SPkto2ZrbQyGX2WJrtCI8bhV8c3R_XIBrhaaKP1qCVuF8-99Dy7psvvqQ-i= zaXcC8QSeEM7PLM8UuUHVrA$ for graphic product... ATTN...WFO...MFR...PQR...SEW... ATTN...RFC...NWRFC...NWC... LAT...LON 48462444 47932366 47282319 46322307 44672328=20 43912349 43612382 43492435 43922463 44862442=20 45692426 46592439 47372467 47862493 48182502=20 48312497=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) .