871 FXUS02 KWBC 260711 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 211 AM EST Fri Dec 26 2025 Valid 12Z Mon Dec 29 2025 - 12Z Fri Jan 02 2026 ...Overview... A broad upper ridge/trough pattern across the Lower 48 to start the week next week will transition to a more typical wavelength trough/ridge/trough pattern. With the Pacific largely blocked from incoming moisture, most of the CONUS will be dry except for downwind of the Great Lakes due to lake-effect snow. By the end of the period, the strong upper ridging initially over the West Coast will break down and allow both northern stream and subtropical troughing to push inland, bringing another round of rain and mountain snow to much of the west by the end of next week (but with much less intensity than the current event). ...Guidance/Predictability Assessment... Overall, the ensemble systems agreed on the synoptic evolution but did differ on the extent of lower heights around the Great Lakes by later next week. The GEFS was higher with heights than the ECMWF EPS, Canadian GEPS, and AI-GEFS, and was discounted. Despite the good agreement at 500mb, there was a large disagreement on temperatures just east of the Divide by later next week as high pressure slips south-southeastward through western Canada, reinforcing a stationary boundary just east of the Rockies. For the deterministic models, each was within the acceptable noise of the ensemble spread and a blend of the 18Z GFS and 12Z ECMWF/Canadian offered a reasonable starting point for the day 3-5 period. Thereafter, used an increased amount of the ECMWF ensemble mean to discount the more robust solutions (e.g., GFS in the Great Lakes/Northeast) noting that any embedded system around the large multi-pronged upper low over Hudson bay has the potential to briefly amplify as it rounds the base of the trough through the Great Lakes. ...Weather/Hazards Highlights... A vigorous system will lead off the period on Monday through the Great Lakes as it rapidly deepens into southeastern Ontario/western Quebec. This will bring a wintry mix of snow/sleet/freezing rain to the Northeast as warm air overrides the cold surface and lake enhanced/effect snow over the Great Lakes as the low promotes northerly to northwesterly flow. The pattern will turn quiet midweek with high pressure in control but continued chance of lake effect snow that will be enhanced by quick clipper systems and/or mid-level troughs. By Thu/Fri, the West will see an increase in precipitation as a front from the Pacific comes into the PacNW and a weakening occluded system out of the subtropical Pacific moves into California and the Southwest. The moisture anomalies will increase, actual rainfall amounts appear to be modest at this time. However, given the recent very heavy rainfall over much of California, this system bears watching. Temperatures will be somewhat variable over the Lower 48, but generally colder than normal around the Great Lakes into the Northeast due to the persistent troughing and milder than normal over the interior West/Rockies. Widespread record cold or warm temperatures are not expected. Fracasso 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 $$