Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Fri Jan 14 2022 Valid 12Z Mon Jan 17 2022 - 12Z Fri Jan 21 2022 ...Major winter storm to lift over the Northern Mid-Atlantic/lower Great Lakes and Northeast Monday... ...Guidance/Predictability Assessment... Models and ensembles have come into closer agreement in the day 3-5 (Mon-Wed) including a major winter storm to bolster forecast confidence. The WPC product suite this period was mainly derived from a GFS/ECMWF/UKMET/Canadian composite along with the 01 UTC National Blend of Models. WPC continuity is well maintained. Predictabilty seems marginally above normal into days 6/7 (Thu-next Fri), but forecast spread does increase in particular with the handling of Pacific system energies into an upper ridge built off the West Coast. Recent ECMWF/UKMET runs bring more upper troughing through this ridge into the Northwest than the Canadian and especially the GFS that deflect energies more over the ridge. Suspect ridge amplitude should hold on the more amplified side of the full envelope of solutions given initial strength, perhaps closest to the 06 UTC GEFS mean. ...Weather Highlights/Hazards... A major winter low developing over the weekend seems set to lift from the northern Mid-Atlantic/lower Great Lakes through the Northeast Monday. This will present a continuing full array of weather hazards and threats. Heavy wrapping snows will spread in earnest along/on the backside of the deepening low and west of the I-95 corridor into interior areas given track. For locations east/along I-95 (including the major metro areas), precipitation may start out as accumulating snow, with a changeover to sleet then rain as warmer air filters in from the east. Gusty winds surrounding the surface low may create high waves off the coast leading to possible coastal flood concerns along the Northeast coastline. After the main low exits northeast of the U.S. by Tuesday, another low pressure system is forecast to track over the north-central U.S. in response to a mid-upper shortwave and bring some snow to the Upper Midwest and Great Lakes then northern New England, with possibly higher totals near typical lake enhancement areas. The West could see some light precipitation during the period, particularly over the Pacific Northwest and into the Northern Rockies, with mainly dry conditions elsewhere. Rain may develop across the Lower Mississippi Valley and Southeast for mid-later next week with modest return Gulf flow with induced wave passages. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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