Extended Forecast Discussion NWS Weather Prediction Center College Park MD 111 AM EST Thu Jan 03 2019 Valid 12Z Sun Jan 06 2019 - 12Z Thu Jan 10 2019 ...Overview, Guidance Evaluation, and Preferences... The models indicate the upper trough moving onshore along the west coast by 12z Sun 06 Jan steadily progresses across the country, reaching the Plains on Mon, Great Lakes on Tue, and then the northeast on Wed 09 Jan. The models and ensembles are in large scale agreement on the pattern with typical timing and phasing differences, particularly over the lower Lakes and northeast on day 7. The manual forecasts blended the 12z ECMWF/12z GFS/12z Canadian Global with the respective 12z ECMWF and 18z GEFS Ensemble Means for days 3-6 before giving more weight to the means on day 7 Thu 10 Jan. In the wake of the developing eastern trough, heights rise in the center of the country, leading to a dry period with warm temperatures in the middle of next week. In the middle of next week, another eastern Pacific system should approach the western coast and move onshore Tue-Wed, and possibly inland on Thu 10 Jan. There is considerable spread in both the timing and phasing of the trough from model to model, run to run, and even among the means. This leads to low confidence as to the location and strength of the trough and lows embedded within the trough. The differences result in a preference for the ensemble means plus an alert to watch for changes in the forecast as there is a large spread in possible solutions in the eastern Pacific, west coast Tue and Wed, and inland to the northern Rockies and Great Basin Thu 10 Jan. ...Weather Highlights/Hazards... The models still indicate periods of precipitation across the coastal states from California to WA, with highest totals this period centered on northwest California, with valley rains and mountain snows. There continues to be potential for locations receiving 5-10 inches liquid in northwest CA for the multi-day totals. Lighter amounts extend inland into the southwest and northern Rockies. With low pressure crossing from the MS Valley towards the Great Lakes Mon-Tue 08 Jan, a stripe of snow is expected in portions of the Great Lakes, with a transition to rain in the Ohio Valley. As the triple point low develops near southern New England, there is potential for the snow to extend east from the Great Lakes across interior New York and central to northern New England, with areas of heavy snow possible. Snow extend from the Lakes into upslope areas of the central Appalachians. Expect temperatures to be above normal over a majority of the Lower 48, though the Northeast may trend down at least to normal by next Wed as upper troughing amplifies over the region. Warm anomalies to the east of the Rockies will be most pronounced on multiple days from the central Plains through the Upper Mississippi Valley and from the southern Plains into Ohio Valley on Sun-Mon. The cool anomalies will be focused in the periods of wet weather near the west coast and Sunday in the southwest. Petersen 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