Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EST Sun Dec 12 2021 Valid 12Z Wed Dec 15 2021 - 12Z Sun Dec 19 2021 ...Guidance/Predictability Assessment... Guidance clustering and forecast spread/predictability through medium range remains much better than normal. The WPC medium range product suite was primarily derived from a composite of the 18 UTC GFS and 12 UTC ECMWF/Canadian along with the 01 UTC National Blend of Models Days 3-7. This blend yielded a solution quite compatible with the previous WPC forecast package and seems well supported by GEFS/NAEFS/ECMWF ensembles. Latest 00 UTC guidance overall remains consistent with this composite through much of the forecast period. ...Weather/Hazards Highlights... A vigorous upper trough will lift northeastward from the Southwest midweek, bringing widespread mountain snow/rain through the Great Basin and northern/central Rockies. As the system lifts through the Plains Wed-Thu, rapid cyclogenesis across the north-central U.S. will 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 midweek with record high temperatures upwards to 30-40F above normal. Modest lead rains that should fall on top of recent Upper Midwest snows together with the record warmth could lead to flooding issues. Anomalous warmth ahead of the trailing cold front, with positive anomalies upwards to 15-25F, will reach the East late week. The moderating front will stall across the Deep South. An axis of enhanced rainfall is forecast to set up from the southern Plains through the Mid-South and the OH Valley/Northeast Fri/next weekend with emerging return flow and organized frontal wave development and lift. A swath of weekend snow may also occur on the cooled northwest periphery of this precipitation shield. Upstream on the heels of the aforementioned lead storm, another moisture surge and moderate to heavy precipitation is forecast to reach northern California and Oregon Wed/Thu as the next Pacific cyclone reaches the West Coast. Guidance signal is also growing that moisture from yet another Pacific system will modestly impact the Pacific Northwest next weekend. Schichtel 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