Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Mon Jan 13 2020 Valid 12Z Thu Jan 16 2020 - 12Z Mon Jan 20 2020 ...Significant Late Week Winter Storm Threat from the Upper Midwest to the Northeast... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of the 18 UTC GEFS mean, 12 UTC ECMWF/ECMWF ensemble mean and the 00 UTC National Blend of Models. This maintains great WPC continuity. Of the deterministic models, the 12 UTC ECMWF seems to best cluster with GEFS/ECMWF ensembles and provides a bit more detail consistent with average predictability and run to run variance. The newer 00 UTC GFS now seems in better alignment with this WPC blend, but the 00 UTC ECMWF has trended slightly weaker and a bit slower like recent runs of the UKMET. They all still have a decent low. ...Weather/Hazard Highlights... An organized lead low will support wrap-around heavy snows over the Northeast Thursday, with lake effect snows in the wake of system passage as a trailing cold front surges Arctic air/high pressure southward across much of the central and eastern U.S. A decent low off the Pacific Northwest Thursday will enhance maritime hazards as amplified upper troughing/ample height falls to the south work inland. This will spread a moderate swath of precipitation across California,the Great Basin/Southwest and Rockies into Friday. This includes a locally heavy and terrain enhanced snow threat. Moderate precipitation should also focus into the Pacific Northwest Friday into the weekend with flow underneath a less certain/defined series of Northeast Pacific lows. The upper trough/height falls will progress northeastward over the north-central and northeast U.S. this weekend overtop a warming/stabilizing Southeast U.S. upper ridge. Cyclogenesis/frontogenesis over the Plains Friday will lead to a risk of weekend deep low track from the Great Lakes/Midwest to the Northeast/Canadian Maritimes. The lead Arctic airmass will recede northward with return flow/moisture influx in advance of system approach, but the stage will be set for a threat of heavy snow/ice from the Upper Midwest/Great Lakes to the northern Mid-Atlantic/Northeast. Lake effect snows linger in the wake of system passage coincident with reinforcing cold air advection. There is also expectation for a swath of moderate to heavy frontal/warm sector rains with some runoff issues from the south-central Plains northeastward toward the Northeast Friday/Saturday. Schichtel 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