Extended Forecast Discussion NWS Weather Prediction Center College Park MD 124 AM EST Sun Dec 15 2019 Valid 12Z Wed Dec 18 2019 - 12Z Sun Dec 22 2019 ...Overview and Guidance/Predictability Assessment... Stormy period for the Pacific Northwest into Northern California with successive systems moving inland. The East will be quieter for the end of the week but a weak system in the central Plains may become more developed off the Southeast coast next weekend. The models and ensembles have waffled in their agreement with the incoming western system on Wednesday and how it travels across the CONUS. Though the east-west timing (speed) has come into better agreement, the north-south track lags behind. Clue from ensembles has shown a trend toward enough separation from northern/southern stream flow that the farther south track seems to still be preferred. This included the 12Z ECMWF/UKMET (though they were rather deep) and the 18Z GFS as the Canadian tracked to the north. This would allow some cyclogenesis over the northeast Gulf and/or off the Southeast/FL coast in the Atlantic around next Sat. Thereafter, ensembles show a wide expanse of solutions, so preferred to take the system eastward but with low confidence. Back to the West, next trough will likely take a front into California after several days of focused rainfall (higher elevation snowfall) via a modest atmospheric river event. ...Weather Highlights/Threats... Precipitation will be centered on the West, particularly coastal OR and northern California. Upper trough in the eastern Pacific will allow a fetch of moisture from near Hawai'i to reach the OR/CA coast with a north/south oscillation between fronts as the trough changes shape upstream. Several inches of precipitation are expected but over a 2-3 day period with a likely break in between. Daytime temperatures will likely be below average with the rainfall but otherwise near average elsewhere and near to above average for overnight lows. East of the Rockies, temperatures may be more variable with a quick cold shot skirting through the Northeast on Thursday (10s/20s for highs and -0s/0s/10s for lows). Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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