Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EST Sun Jan 13 2019 Valid 12Z Wed Jan 16 2019 - 12Z Sun Jan 20 2019 ...California Heavy Precipitation... ...Cold air surges through the North-Central U.S... ...Central to Eastern U.S. Heavy Rain/Snow Threat Next Weekend... ...Guidance Evaluation/Preferences... While the overall larger scale flow pattern evolution remains reasonably well supported in guidance, an uncertain split of smaller scale energies over the eastern Pacific and subsequent progression inland across North America continues to offer significant run to run differences in deterministic guidance from short through medium range time scales. Accordingly, the WPC medium range product suite was primarily derived from a blend of more compatable GEFS/NAEFS/ECMWF ensemble means. This holds reasonable WPC continuity. ...Weather Highlights/Hazards... In this solution, ample southern stream mid-upper level trough energy/height falls impact California and to a lesser extent the Pacific Northwest Wed/Thu to produce additional heavy rain/mountain snows. A moderating swath of activity in this stream works inland across the Intermountain West and Rockies into Friday before the approach of an amplified Pacific trough over the northeastern Pacific switches focus to the Northwest next weekend. Downstream, glancing blows of cold Canadian air past midweek over the central to eastern U.S. northern tier become more significant/longer lasting and increasingly southward surging later week into next weekend with northern stream amplification. This occurs as ample southern stream energies eject underneath from the western U.S. to spawn s-central to eastern U.S. cyclogenesis/frontogenesis. Deepening moisture influx into the system and overrunning the cold airmass spilled overtop would combine with dynamics to fuel an increasingly robust moisture/precipitation shield that offers a significant threat for heavy warm sector rains/convection and a widespread swath of heavy snow/ice to the north. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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