Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Dec 11 2021 Valid 12Z Tue Dec 14 2021 - 12Z Sat Dec 18 2021 ...Another moisture surge is forecast to reach northern California and Oregon midweek as heavy precipitation winds down in southern California... ...Record warmth to spread from the central U.S. toward the snow-covered region of upper Midwest ahead of an intensifying cyclone... ...Guidance/Predictability Assessment... Model and ensemble forecast clustering and spread through most of the medium range remains much better than normal, bolstering forecast confidence. The WPC medium range forecast package was based on 40% from the 06Z GFS and GEFS, 40% from the 00Z ECMWF/EC mean, and 20% from the 00Z CMC/CMC mean. More weights from the ensemble means were applied starting from Day 5.5. This blend yielded a solution quite compatible with the previous WPC forecast package. ...Weather/Hazards Highlights... An amplified upper trough will push onshore into the Southwest next Tuesday into Wednesday. Widespread terrain-enhanced rainfall and heavy mountain snows over southern California on Tuesday will likely wind down by Wednesday as the trough pushes inland and then lifts northeastward through the western U.S. midweek, bringing widespread mountain snow/rain through the Great Basin and northern/central Rockies. As the main system lifts northeastward through the Plains next Wed-Thu, the possibility of rapid cyclogenesis across the northern U.S. will likely lead to an expansive area of strong winds, together with a swath of wintry precipitation through the north side of the low track across the northern Plains and upper Midwest to the upper Great Lakes. Ahead of the deep cyclone, an upper ridge will build over the central U.S. where anomalous warmth will be most pronounced across the central U.S. In fact, record high temperatures upwards to 40F above normal next Wednesday will likely spread toward a region of the upper Midwest where significant amounts of snow just fell recently. Any rain that should fall on top of the snow together with the record warmth could lead to flooding issues. Behind the amplified upper trough, another moisture surge is forecast to reach northern California and Oregon midweek as the next Pacific cyclone approaches the West Coast. Moderate to heavy precipitation should continue across these areas through midweek. It appears that moisture from the next Pacific system will impact the Pacific Northwest on Friday and into the weekend. On the East Coast, anomalous warmth ahead of a cold front will reach the area late next week. Meanwhile, the trailing portion of the cold front will likely become nearly stationary across the Deep South where an axis of enhanced rainfall is forecast to set up across the southern Plains through the Tennessee Valley. Kong 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, winter weather outlook probabilities and heat indices are at: 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml