Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1028 AM EST Tue Dec 29 2020 Valid 12Z Fri Jan 01 2021 - 12Z Tue Jan 05 2021 ...Strong storm system to affect the Northeast to bring in the New Year, and multiple Pacific systems for the Northwest... ...Weather Pattern Overview... The weather pattern will be active/progressive from late this week into next week, with a strong low pressure system developing over the southern Plains by early Friday. The surface low remains well developed as it tracks towards the Great Lakes and Northeast states by Saturday morning, with a strong cold front following in its wake. A quasi-zonal mid-upper level flow pattern develops by the beginning of next week as the eastern U.S. upper trough departs. Three separate northeast Pacific storm systems will impact the Pacific Northeast and northern Rockies, leading to a rather unsettled start of the new year. ...Guidance/Predictability Assessment... The 00Z/06Z model guidance, along with the 00Z ECMWF and NAEFS ensemble means, are in relatively good agreement throughout the period. Detail issues exist, with the ECMWF/UKMET slower with the trailing shortwave/upper low that follows behind the cyclone impacting the Great Lakes and Northeast. The CMC gets toward the ECMWF/UKMET a different way, through a northern stream shortwave rather than a lagging shortwave/closed low in the southern stream. The WPC medium range QPF, fronts, winds, and pressures were primarily derived from a blend of the 06z GFS, 00z Canadian, 00z UKMET, 00z ECMWF, 12Z ECMWF ensemble mean, the 00z NAEFS mean. ...Weather/Threats Highlights... More active weather is expected across the central and eastern U.S. to bring in the New Year. A corridor of moderate to locally heavy snow is anticipated from eastern Kansas to the northern Great Lakes region as the surface low lifts northeastward, and depending on the eventual strength of the low and the resulting pressure gradient, blizzard conditions may once again be possible for some portions of Iowa and Wisconsin. Below average temperatures are expected in the Southern Plains on Friday before temperatures rebound closer to average. While some lake effect snow is likely once the surface cyclone exits the Northeast by the weekend, temperatures in the East, Great Lakes, and Southeast are forecast to be near to above average from Friday into next Tuesday. In the warm sector of the low, more unneeded rain is expected from Florida and extending northward across the Mid-Atlantic, Appalachians, and then New England. However, rainfall totals are expected to be a little less than the Christmas storm. Ground conditions are saturated across many of these areas, and this additional rainfall may result in some instances of increased run-off and rising river levels. Some severe storms are also within the realm of possibility across portions of the Southeast states, along with above normal temperatures. Meanwhile, areas from the Pacific Northwest to central California will continue to see additional rounds of rain and mountain snow late this week and through early next week with the approach of multiple Pacific systems in progressive flow aloft. The highest precipitation totals are expected to occur over the favored coastal terrain and also the Cascades and Sierra, with an atmospheric river event possible over the weekend for western Oregon and Washington. Several inches of rainfall will be possible for some of these areas. Temperatures in the West will be near to slightly above average through the period. Roth/Hamrick 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