Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1035 AM EST Thu Jan 02 2020 Valid 12Z Sun Jan 05 2020 - 12Z Thu Jan 09 2020 ...Overview/Guidance Assessment... A progressive westerly flow pattern is on tap for next week for the CONUS. Uncertainty regarding track and intensity of embedded shortwaves remains the main concern with the greatest uncertainty with a trough/low potentially developing over the Great Lakes region and shifting northeast from there in the middle of next week The initial deep cyclone pivoting into a negatively tilted trough exits the Northeast coast Sunday. The 00Z CMC remains too quick with the system and the GFS is now the farthest west/closest to the New England coast. However, clustering is decent with the ECMWF/UKMET/GFS, so a preference is for the 00Z ECMWF/UKMET with some GFS. The progression of the shortwave initially over the northern Great Plains Sunday looks to play a key role in subsequent development east from there toward the midweek as remnants may interact with the next trough that quickly shifts inland across the western CONUS Sunday. The GFS shears less of this trough, allowing a closed mid-level low to develop over/just north of the Great Lakes Monday. A similar pattern is seen in the UKMET, just displaced a bit north. The presence of this low disrupts development of the next trough as it pushes across the northern Plains Monday/Monday night and results in minor surface low development. The 00Z ECMWF by contrast shears the middle trough and ejects it from the Great Lakes, allowing rapid trough/low development over the Upper Midwest/Great Lakes Monday night into Tuesday. This deepening low then closes off and tracks northeast over eastern Canada into Wednesday night/into Day 7. Given this deterministic difference, ensemble means are brought into the blend a bit sooner than normal with the 06Z GEFS/00Z ECENS (which agree on general troughing instead of closed lows) receiving weight in the WPC blend Monday night and the dominant source by Wednesday night/Day 5 into Day 6. This results in a much weaker low than the deterministic 00Z ECMWF for Tuesday and Wednesday. This weight toward ensemble means starting on Day 4 also works for the next trough reaching the West Coast Tuesday night. ...Weather Highlights/Threats... The active pattern into the northwestern CONUS keeps the Pacific Northwest and northern Rockies in repeating precipitation through at least the middle of next week. This precipitation will focus over coastal locations and the Coastal Range/Cascades and result in a heavy rain threat for areas below the snow level. The magnitude and placement of snow around the Great Lakes and potential heavier rain over the already saturated TN Valley depends on the evolution of the trough/surface low development across the Central U.S. Tuesday and Wednesday. Confidence remains low on the central CONUS precipitation. With a fast west-to-east flow across the country, no strong outbreaks of arctic air are anticipated. This will lead to generally near and above normal temperatures across the CONUS through the midweek. Jackson 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