Extended Forecast Discussion NWS Weather Prediction Center College Park MD 956 PM EST Tue Jan 01 2019 Valid 12Z Sat Jan 05 2019 - 12Z Wed Jan 09 2019 ...Overview... As a negatively tilted trough strengthens offshore western North America, mid-level height anomalies become ever more anomalous across the Midwest and Great Lakes. This supports a strengthening negatively tilted trough with an embedded upper low across Atlantic Canada with time. ...Guidance Evaluation/Preferences... Broadly, the guidance shows reasonable agreement between the deterministic and ensemble mean guidance. Detail issues are numerous, though mainly due to variable strength moreso than progression when compared to this time yesterday. The only model that appeared to be a notable outlier was the 12z Canadian from late Tuesday into next Wednesday. As such, the 500 hPa heights, pressures, winds, and fronts began with an even blend of the 12z Canadian/12z UKMET/12z ECMWF/18z GFS. The ECMWF and bias-corrected NAEFS were introduced on Monday with increasing weight by next Wednesday, which the Canadian was slowly phased out by mid next week. This led to some slowing of the system expected to move from Mid-Continent across the Great Lakes and Northeast early to mid next week, but otherwise rather good continuity. The remainder of the lower 48 grids were composed of a more even blend between the deterministic and ensemble mean guidance through the period to account for uncertainty in these more variable quantities (temperature, dew point, clouds, and precipitation chances). ...Weather Highlights/Hazards... The overall pattern should be favorable for significant rainfall and high elevation snow near the West Coast due to persistent southwesterly flow off the Pacific. Areas near northern California with be wet at lower elevation/white at elevation some locations possibly receiving at least 5-10 inches liquid Saturday into next Wednesday. Favored locations over western Washington/Oregon and the northern Continental Divide will likely see significant totals as well. In less extreme fashion some moisture should extend farther southward over California, Arizona, and the Interior West/Rockies. Depending on how systems materialize near the West Coast, there could be areas with strong winds. Over the East, the system tracking by the Mid-Atlantic coast this weekend should produce some areas of locally moderate to heavy rainfall from the Mid-Atlantic into southern New England, just north of the upper low track. The majority of precipitation with this system should be in the form of rain. Any wintry precip types should be confined to the very northern/northwestern fringe of the moisture shield. A wavy frontal system emerging from the Plains may bring an episode of light to moderate precipitation to parts of the eastern half of the Lower 48 during the latter half of the period. Wintry precip types should again be confined to more northern latitudes. Temperatures are expected to be slightly below average across the Southwest Saturday. Otherwise, mild to seasonally warm temperatures are expected, with temperatures near to above average elsewhere and elsewhen across the lower 48 during the medium range period. Some locations over the extreme Northern Tier and Midwest could see bouts of 20F+ above normal temperatures Saturday through Tuesday. Roth 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