Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Jan 01 2022 Valid 12Z Tue Jan 04 2022 - 12Z Sat Jan 08 2022 ...Multi-system coastal heavy rain and mountain focusing heavy snow threat from the Pacific Northwest/northern California to the north-central Great Basin/Rockies next week... ...Arctic blasts spread out from the north-central U.S. to fuel a mid-later next week heavy snow threat from the Great Lakes/Ohio Valley/Appalachians to the Northeast with coastal storm genesis... ...Pattern Overview and Weather/Hazard Highlights... A deepening storm will track from the northern Plains Tue to the Great Lakes and eastern Canada Wed/Thu. Arctic air will dig across the central then eastern U.S. behind the windy and precipitation focusing low to include a threat of plowable snow from the Great Lakes/Ohio Valley/Appalachians to the Northeast, with trailing frontal rains down to the Southeast. The snow threat is expected to be exacerbated by lake effect, terrain lift and over the Northeast by coastal storm genesis into Fri. Meanwhile, multiple Pacific systems with moderate atmospheric river blueprints will meanwhile take aim at the Pacific Northwest/northern CA next week, that will fuel multi-day coastal rainfall and terrain/mountain enhancing snows. Energies will work inland across a snowy north-central Great Basin/Rockies where lift will be further enhanced by post-frontal upslope. ...Guidance/Predictability Assessment... Model and ensemble forecast spread and uncertainty now seems lower than normal through medium range time scales. A composite of well clustered mass field guidance from the 06 UTC GFS/GEFS mean, 00 UTC ECMWF/ECMWF ensemble mean/UKMET/Canadian along with the 13 UTC National Blend of Models seems to offer a good basis for the WPC product suite for days 3-7 (Tue-next Sat) in a pattern with good continuity. The composite tends to mitigate lingering embedded system timing/strength differences and run to run variable lower atmospheric temperature profiles consistent with predictability. For example the blend addresses a 06 GFS that seems too warm in the Arctic air over the northern Plains Day 4/Wed, the 00 UTC Canadian seems too aggressive with northern High Plains Arctic air Day 6/7, and recent ECMWF run to run temperature continuity has overall been less than stellar. 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