Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sun Jan 31 2021 Valid 12Z Wed Feb 03 2021 - 12Z Sun Feb 07 2021 ...Midweek Southwest U.S. system to progress to the Plains/Midwest/Northeast later week followed by arctic outbreak by weekend... ...Guidance/Predictability Assessment... As the deep low gradually weakens and exits New England, the next system of concern during the medium range period will be over the Plains where global models continue to show difficulties in the timing and degree of interaction between an upper trough lifting and ejecting into the central Plains, and a surge of polar air mass from central Canada. There remains noticeable discrepancy regarding the track and intensity of frontal waves that may form later next week over the central Plains among the deterministic solutions from global models. However, the consensus of this morning's ensemble means yield a consolidating low pressure system which is forecast to track across the Great Lakes early on Friday--a solution that compares well with WPC continuity. Thereafter, models indicate decent agreement for the low to shear off to the east across New England as an outbreak of arctic air from Canada becomes increasingly likely down the Plains by next weekend. Elsewhere, the GFS indicates intensification of a frontal wave across the Southeast and the East Coast late in the week but this scenario is not supported by its ensemble mean nor by the ECMWF and the CMC solutions. The WPC medium range forecast package was based on the consensus of the 00Z ECMWF/EC mean, the 06Z GFS/GEFS, the 13Z NBM, and a smaller contribution from the 00Z CMC/CMC mean. More of the ensemble means were used on Days 6 and 7, with the least contributions from the 06Z GFS and 00Z CMC. ...Weather/Threats Highlights... For the deep cyclone near New England, wintry precipitation inland should gradually taper off on Wednesday but some areas along or offshore the coast will continue to experience brisk to strong winds into Thursday as the cyclone will be slow to depart. A strong upper trough driving through California Wednesday will support a period of enhanced moisture/rains and mountain snows, with activity spreading across the south-central Great Basin/Rockies into Thursday. Variance with the extent of digging still leads to subsequent ejection model differences which grow downstream along with uncertain stream phasing/central U.S. storm genesis mid-later next week. It is expected that as the energy comes out of the West and Rockies, a deepening low or lows to the lee of the Rockies will lift toward the Great Lakes late Thursday to Friday. Leading warm air advection and moisture return on the backside of the departing high will allow deepening Gulf moisture to interact with the favorable dynamics and forcing. This will fuel an expanding area of moderate to locally heavier precipitation across the east-central U.S. Enhanced wrap-back snows can be expected near and to the north of the main cyclone track over the north-central to northeastern U.S., and could dip farther south into the Tennessee Valley early on Saturday behind the system. However, low support aloft/phasing details remain uncertain. Upstream, another batch of wintry precipitation is forecast to track down across the Northwest and then the northern and central Rockies late week associated with an arctic front. With the approach of new digging upper trough energies, lead ejecting waves and main upper trough amplification back over the central U.S. next weekend may favor some uncertain modest swaths of snows from the Midwest/OH Valley to the Appalachians and the Northeast, including some lake-effect enhancement and focus. Kong/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