Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1102 AM EST Sat Jan 12 2019 Valid 12Z Tue Jan 15 2019 - 12Z Sat Jan 19 2019 ...Heavy precipitation for California next week... ...Turning much colder for the Upper Midwest... ...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. As the last in the series of western CONUS fronts moves out of the Rockies next Friday, the precipitation focus will shift out of the west and through the east-central states into next weekend as arctic cold spills into the northern tier. ...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. A blend of the deterministic GFS/ECMWF/UKMET was used to form the starting point for the Tue-Thu forecast. Preferred a more southerly position of the sfc/upper low off the WA/OR coast next Thu compared to the ensemble means which were likely stretched NW/SE due to upstream differences in incoming shortwaves. This also fit the trend seen in the past few runs of the ECMWF ensemble mean. For Fri-Sat next week, the western system will push out of the Rockies and into the Plains as an arctic front drops out of southern Canada and sinks eastward and southward overtop the Pacific front. This may set up a potentially impactful winter storm (and significant rainfall to the south) for the eastern states next weekend as the system slides eastward. ...Weather Highlights/Hazards... The West Coast will remain quite active with nearly a frontal system a day Tue-Thu. The heaviest precipitation (low elevation rain and mountain snow) will focus across coastal California and the Sierras with still significant inland/valley rainfall along I-5 but also east of the mountains into Nevada. Total precipitation amounts over the period will likely exceed 4 to 8 inches (liquid) in the Sierra and Coastal Ranges which will mean well over 100" of snowfall during the period at favored jackpot areas. Significant precipitation will spread through Nevada as well but especially with the last system on Thursday, focused on the southern half of the Silver state. Friday into next weekend, arctic air will sink southward and spread eastward out of southern Canada into the northern tier where temperatures will struggle to reach above zero over parts of North Dakota and Minnesota and overnight temperatures may reach into the -20s. This cold airmass will support snowfall expanding eastward out of the Plains toward the Ohio Valley next weekend and increased rainfall ahead of the cold front moving out of Texas. This will have to be monitored for future weather hazards into the easts as it progresses eastward next Saturday/Sunday. Fracasso/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