390 FXUS02 KWBC 072005 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 305 PM EST Sun Dec 7 2025 Valid 12Z Wed Dec 10 2025 - 12Z Sun Dec 14 2025 ...Potent/Persistent Atmospheric River continues to bring heavy rain and high mountain snow to the Pacific Northwest into Thursday... ...Overview... A broad upper level trough with reinforcing shortwaves will continue to dominate areas east of the Rockies with broad ridging persisting along the West Coast through this weekend. Strong westerly flow over the western ridge will continue to bring an atmospheric river through the Northwest and Northern Rockies with heavy rain and high elevation snow into Thursday, along with high winds. Cold weather and clipper systems will be favored in this pattern east of the Rockies with enhanced northern tier wind/snow chances and following lake effect snow in the lee of the Great Lakes. ...Guidance/Predictability Assessment... Positioning of the remaining/lingering deep cold core lows is a main question for the Wednesday to Friday timeframe. Global deterministics, especially the 00Z ECMWF/06Z GFS have been farther north near James Bay while the 06Z ECAIFS and the 00Z CMC were farther south was near Georgian Bay. Given the valuable insights the ECAIFS has made for large scale positioning, the WPC forecast from this morning was heavily weighed toward the 06Z ECAIFS and the 00Z CMC. However, there has been a bit of a shift toward a consensus solution between James and Georgian Bays with the 12Z suite. Timing of shortwave troughs around this gyre remain uncertain given the transient nature of these shortwaves and impulses. QPF wise, the 13Z NBM was blended with the 00Z CMC/EC with some enhancements from the 06Z ECAIFS. Of note is a northward trend in the atmospheric river, more into WA than OR, on Day 4. ...Weather/Hazards Highlights... Persistent AR into Thursday. Precipitable water values approaching 1.5" not far offshore with 50+ kts of low-level inflow from the Pacific plenty of heavy rain and high snow levels. The Day 4 Slight Risk was shifted north a bit to include more of the WA Cascades and less OR per consensus of the 12Z guidance. Elsewhere, clipper systems will bring rounds of precipitation, mainly snow, over a cold northern Plains and Midwest, Great Lakes/Appalachians, and the Northeast next week. Aforementioned surface cyclo/fronto genesis will act to enhance wrapping activity and especially Lake Effect with system passages. Wavy and stalling trailing fronts lingering down off southern Florida and into the Gulf may also focus uncertain rain chances near the Coast by Friday. Strong temperature gradient forecast along the Rockies Thursday into this weekend areas west 15-25F above normal with a polar front shifting from Canada starting on Thursday. Max temps 20 to 30 degrees below normal over the northern Plains Friday spread across the Midwest Saturday, reaching the Eastern Seaboard Sunday. Jackson Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$