Extended Forecast Discussion NWS Weather Prediction Center College Park MD 120 AM EST Sat Jan 12 2019 Valid 12Z Tue Jan 15 2019 - 12Z Sat Jan 19 2019 ...California Heavy Precipitation Pattern Next Week... ...Overview... It remains the case that steadily progressive and amplified Pacific flow will bring a series of significant storms to the West Coast next week. As these systems move eastward, split flow will emerge around an amplified downstream Great Basin/Rockies upper ridge. Northern stream energy will amplify as it enters broad cyclonic upper-level flow east of the ridge, with frequent shortwaves and mean upper troughing from the Upper Midwest to the Northeast. Meanwhile, an active West Coast will feature amplified trough/upper lows to especially threaten California all next week. Unsettled flow/organized precipitation spreads increasingly inland over the West later next week and east-central U.S. next weekend. ...Guidance Evaluation/Preferences... Model agreement during the forecast period was fairly good in the large scale, with smaller features such as shortwaves moving through the northern tier of the U.S. and the West not handled as well from run to run. The deterministic GFS and EC and the GEFS and ECENS were used to derive the WPC forecast into midweek, with most emphasis applied to ensemble mean guidance in the days 5-7 timeframe amid growing uncertainty. Despite model uncertainties in the details, forecast confidence is high for the threat of heavy precipitation focused in California next week. ...Weather Highlights/Hazards... The West Coast will remain quite active given the rapid frequency of shortwave energies and frontal systems. The heaviest precipitation (low elevation rain and mountain snow) will focus across California, with multiple rounds of precipitation possible through this forecast period. Total precipitation amounts over the period will be heavy, with upslope flow enhancing QPF to 4 to 8 inches plus in the Sierra and Coastal Ranges. Later in the week into next weekend, organized heavier precipitation/cooling is also expected to spread over the Pacific Northwest and then work inland across the West in a pattern as heights lower with more amplified Pacific mid-upper level trough passage. Downstream, a temperature pattern change is also expected for the central U.S. and Northeast tier as a leading series of cold high surges dig southward from Canada. There is an increasing guidance signal that ejecting energy interaction with a lead baroclinic zone may spawn east-central U.S. cyclogensis and increasingly favorable precipitation fueling thetae influx from the Gulf of Mexico next weekend. 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