238 FXUS02 KWBC 280715 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 215 AM EST Sun Dec 28 2025 Valid 12Z Wed Dec 31 2025 - 12Z Sun Jan 4 2026 ...Overview... An amplified upper level pattern is expected to be in place across the Continental U.S. to start the forecast period Wednesday, with an upper ridge situated over the West Coast region and a broad upper trough east of the Mississippi River. This remains the case going into Thursday, with a reinforcing cold front across the East, and the upper ridge moves inland across the Intermountain West and Rockies. The ridge then breaks down some as a couple of Pacific storm systems reach the West Coast. As a result, rain and mountain snow makes a return by the end of the week across the West Coast region, and lake effect snow will be common downwind of the Great Lakes with below average temperatures from the northern Plains to the Northeast states. ...Guidance/Predictability Assessment... The latest deterministic model guidance indicates solid overall agreement with the synoptic pattern through Thursday, and a general blend of the guidance suffices for fronts and pressures. The best agreement is noted across the eastern U.S. with the broad upper level trough pattern in place. More question marks arise with the eventual flattening of the Western U.S. ridge as Pacific shortwave energy from both the subtropics and the northeast Pacific moves towards the West Coast towards the end of the week and beyond. While overall guidance remains in decently good agreement for the eastern half of the country, model spread deteriorates substantially from the Rockies to the West Coast. This includes noteworthy differences between the operational GFS/ECMWF and their respective ensemble means and AI models, with no clear preference by Saturday as the models are struggling with the pattern change across the West. This lead to ensemble means accounting for about 70% of the fronts/pressures forecast by next Sunday. In terms of the NBM, QPF/PoPs values continue to be raised near the Great Lakes/Ohio Valley through the end of the week with a likely low bias in the NBM across this region. ...Weather/Hazards Highlights... Lake effect snow is expected from Michigan to Upstate New York with strong cold air advection across the Great Lakes through Thursday. Some heavy accumulations are likely over the course of Tuesday through Thursday, particularly across portions of Upstate New York where 1-2 feet is well within the realm of possibility, and some additional snow is likely going into Friday as well. Some upslope snows are also likely across the central Appalachians, and light snow from a clipper type system is expected from the Midwest to the Ohio Valley. This system will reinforce the cold airmass that will already be in place, but probably not cold enough to establish many record lows. In terms of heavy rainfall prospects, most of the country should be devoid of that through Wednesday night as surface high pressure governs the weather pattern across the majority of the country. A weakening occluded low pressure system from the subtropics will head in the general direction of southern California, and bring light to perhaps moderate rainfall between 00Z-12Z Thursday, but model guidance suggests the more impactful rainfall doesn't arrive until after 12Z Thursday. After that, a modest surge of moisture from the Pacific increases rainfall coverage across the Transverse Ranges of southern California and also the Peninsular Range, and a Marginal Risk area has been added here for the new Day 5/Thursday excessive rainfall outlook. Moderate to heavy snow is also probable for the Sierra next Thursday/Friday, with expanding precipitation chances more broadly across much of the West, although model solutions still differ quite a bit regarding specifics. Moist return flow along a frontal boundary across the Southeast may bring increasing rainfall chances next weekend, though with significant uncertainty on coverage and amounts here as well. A temperature dichotomy will continue to exist across the country for the middle to end of the week with below average temperatures from the northern Plains to the Mid-Atlantic/Northeast, and above average across much of the West and western High Plains to the western Gulf Coast. The coldest conditions are expected to reside across the Upper Midwest, where highs from 0 to 15 degrees will be commonplace on Thursday with the renewed surge of arctic air. Meanwhile, highs well into the 60s and 70s will likely continue for much of the southern Plains as this area should remain south of the jet stream. Hamrick 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 $$