Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Tue Feb 02 2021 Valid 12Z Fri Feb 05 2021 - 12Z Tue Feb 09 2021 ...Major Arctic Outbreak for the Central and Eastern U.S... ...Pattern Overview and Guidance/Predictability Assessment... The latest medium range models and ensembles offer reasonably well clustered mid-larger scale guidance. The upper pattern will highlight an amplified ridge over the eastern Pacific/Alaska and an amplified longwave trough over central North America. A series shortwaves will dig to the lee of the ridge to reinforce the mean trough position. This will allow for a significant intrusion of Arctic air to overspread and hold a firm grip on much of the central and eastern U.S.. Shortwave details often prove difficult to pinpoint at medium range time scales, but offer multiple opportunities to induce frontal waves and swaths of wintry precipitation in the widespread cold airmass. The WPC medium range product suite was accordingly derived from a composite blend of the 18 UTC GFS/GEFS mean and the 12 UTC ECMWF/Canadian and ECMWF ensemble mean along with the 01 UTC National Blend of Models. This solution maintains good WPC continuity and a composite of latest 00 UTC model and ensemble guidance still seems in line. ...Weather/Threats Highlights... A deepening low will organize and lift to the Great Lakes into Friday. Enhanced snows are expected near and to the north of the main cyclone track from the windy Midwest/Great Lakes to the Northeast. A wavy trailing front will focus some showers and thunderstorms down along the east coast. Meanwhile upstream, expect a swath of heavy terrain snows from the Northwest to the north-central Rockies as a potent shortwaves digs over the region. This energy and subsequent systems will dive into an amplified central U.S. upper trough position this weekend into next week. This will correspond with two main surges a frigid arctic airmass fully southward through the central then eastern U.S.. Trough and cold air reinforcement will interact with the lingering wavy front over the Southeast/East to favor Piedmont/coastal rains and inland snows from the OH Valley/Appalachians to the Northeast, though there is much uncertainty with possible coastal storm development from the Mid-Atlantic to Northeast late in the weekend to early next week. Later period energy progression dug into the south-central states early next week could emerge. Temperature departures will reach 15-30F over the northern tier and Great Lakes by day 5/6 and overspread the East Coast by day 7. For portions of the northern Plains and Upper Midwest, readings may not break 0. The much below normal temperatures will even spread southward into portions of the Deep South and north Florida where daytime high departures of 5-15F are possible. 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