Extended Forecast Discussion NWS Weather Prediction Center College Park MD 206 AM EST Fri Dec 04 2020 Valid 12Z Mon Dec 07 2020 - 12Z Fri Dec 11 2020 ...Overview... A Nor'easter will be pulling away from coastal Maine on Sunday after potentially spreading heavy precipitation across the Mid-Atlantic and Northeast regions over the weekend. Troughing over the East is expected to stay in place, but will slowly de-amplify through the extended period. An upper trough is forecast to drop southward across the western U.S. early in the week, close off, and settle west of Baja California underneath zonal flow/ridging over the Northwest. This feature will likely get pulled back inland into the Southwest in some form around Thursday. ...Guidance Evaluation/Preferences... The large-scale pattern for the next week will consist of a trough across the East and another trough entering the West and diving south/southeast into the Southwest. Model guidance have struggled with various features that affect timing, location and magnitude of systems leaving the East and those entering the West/Plains. Unfortunately the latest guidance has not resolved these issues. However, the overall evolution over the next week remains somewhat agreeable. The GFS and EC have now swapped trends, where the GFS is little faster and on the eastern side of the cluster while the EC is now holding back and is on the western periphery of the guidance. Their respective means are fairly similar to deterministic solutions. The UKMET and CMC fell between the two. In general, the low exiting the New England region was handled well and favored a slower departure. For the West, preferred a multi-model solution for the low that develops. Although the GFS is more progressive, including with the slower EC brings the solution closer to the depiction of the CMC/UKMET. So for this issuance, the blend comprised of the ECWMF/EC ensemble means/GFS/GEFS means/CMC/UKMET. ...Sensible Weather and Hazards... Any lingering precipitation across the East will be light on Monday in the wake an exiting winter storm system. A majority of the country will be mostly dry through the rest of the week/weekend. Onshore flow near the Pacific Northwest will lead to multiple periods of light to modest valley rain and mountain snow for the Coastal and Cascades ranges, and at times, spreading over parts of the Northern Rockies as well. Early in the week Florida will have light amounts of precipitation as the front passes through the state and then slows offshore. As the week progresses there may be increasing chances for light rain to develop over parts of the Desert Southwest and eastward toward Texas as an upper-level low/trough approaches. Ridging will promote milder than normal temperatures for the High Plains to Upper Midwest/Corn Belt into the central Plains, perhaps by 15-25 degrees. Actual temperature readings will approach 60 degrees as far north as South Dakota on Tuesday. Colder than normal temperatures are favored for much of the East to start the period (Sun-Tue) before trending back toward more typical values. Campbell 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