Extended Forecast Discussion NWS Weather Prediction Center College Park MD 123 PM EST Sat Nov 28 2020 Valid 12Z Tue Dec 01 2020 - 12Z Sat Dec 05 2020 ...Active pattern through the week... ...Guidance Evaluation/Preferences... The synoptic pattern takes on an increasingly amplified/blocky pattern over the course of the medium range period (Dec 1-5). First, the East Coast low will continue to lift northward as it occludes with any heavy rain threat ending early on Tuesday. Wrap around moisture over the eastern Great Lakes will favor modest lake effect snows and overall the latest model guidance has locked onto this idea such that any model differences with this system were smaller scale. The main forecast conundrum was the evolution of Pacific energy dropping through the Rockies into the Plains. The GFS remained a faster, flatter, more progressive solution while the UKMET/ECMWF and CMC to some degree favor a slower, digging shortwave that closes off over the south-central Plains. The 06Z GFS appeared more usable than its 00Z run but still more of an outlier compared to the better agreement seen in the ECMWF/CMC. This also lies near the ECENS/GEFS means, which takes the mid/upper level low toward the Mid-MS River Valley by day 7. Southern stream energy will also favor low pressure development over the Gulf Coast that could track toward the Southeast U.S. by day 7, but there's still much spread in guidance. Expect varied and at times boisterous model solutions until more certainty is shown. Course of least regret will be the ensemble means, and preferably the ECMWF ensemble mean which often performs well in amplified/blocky flow. ...Sensible Weather and Hazards... In the wake of the low pressure and associated cold front passage early Tuesday, colder wrap around moisture will result in modest lake effect and upslope snow where the latest winter weather outlook shows moderate to high probabilities of exceeding 0.25" liquid equivalent downwind of Lake Erie and portions of the high terrain in West Virginia. Temperatures will be also be below normal, most pronounced over the Mid-Atlantic to Southeast and Florida where departures of nearly 20F are possible. The next weather system moves through the Western U.S. early in the period then drops into the south-central Plains by Wednesday. Forecast uncertainty is higher than normal, but low pressure near the Gulf Coast is forecast to then develop or move up the Southeast U.S. coast with modest precipitation return/flow ahead of it. Meanwhile, the increasingly amplified pattern across the CONUS will feature positive height anomalies for the Pacific Northwest to northern Rockies where temperatures will trend above normal. Fracasso/Taylor 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