Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM 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 most recent deterministic and ensemble guidance shows remarkably good agreement and clustering for the upper level pattern through the period. A deep, longwave trough is forecast to center itself over central/eastern US through much of the period, with an anomalous closed low north of the Great Lakes. 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.. Before that though, low pressure forming off an old boundary off the Southeast U.S. coast is forecast to lift northeast along the East Coast this weekend. There remains some phasing differences in the models - where the GFS/CMC offer a faster, split solution which would keep any meaningful winter precipitation mostly offshore. However, the ECMWF continues to suggest a slower, more phased scenario with its low pressure riding up along the coast, overspreading much more precipitation inland into the colder air. This solution would bring a higher chance of meaningful amounts of winter precipitation. Much uncertainty remains though and the WPC blend/products favored a consensus approach at this time. Toward the end of the period, the trough begins to flatten out as more progressive/quasi-zonal flow takes shape. Individual shortwaves will parade through the deep northwest flow initially where there are some timing/strengths differences and by the end of the period, interactions along the southern boundary will result in an area of low pressure forming over the southern Plains. This cycle of the WPC blend was composed mainly of the 00Z ECMWF/CMC, 06Z GFS initially with increasing weight given to the ECENS/GEFS means by day 6/7 to account for some of the model bias and uncertainty. Overall though, forecast confidence was average to above average through the period. ...Weather/Threats Highlights... Deepening low pressure lifting out of the Great Lakes early in the period will bring some enhanced snowfall near and to the north of the main cyclone track along with blustery/windy conditions on the backside. This will also enhance some lake effect snows. 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 and produce periodic swaths of snows. Low pressure developing off the Southeast coast on an old residual boundary could lift northeast and produce precipitation across portions of the Mid-Atlantic, Northeast, and New England...though there is much uncertainty in the phasing of this low and mid/upper level energy. Winter Weather Outlook probabilities are in the 30-50 percent range for meaningful amounts of snow. Finally, by day 7, there is an emerging guidance signal that later period energy progression dug into the base of the mean upper trough early next week may offer potential for an inland precipitation signature out from the south-central states that could offer a widespread threat of overrunning snow/ice on the northern periphery of activity. Taylor 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 Hazards: - Heavy precipitation across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, the Ohio Valley, and the Tennessee Valley, Tue, Feb 9. - Heavy snow across portions of the Great Lakes and the Upper Mississippi Valley, Fri, Feb 5. - Heavy snow across portions of the Northeast and the Great Lakes, Fri-Sat, Feb 5-Feb 6 and Mon, Feb 8. - Heavy snow across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Mon, Feb 8. - Much below normal temperatures across portions of the Central Plains, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Sun-Tue, Feb 7-Feb 9. - Much below normal temperatures across portions of the Central Plains, the Northern Plains, the Northern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Great Lakes, Sat-Tue, Feb 6-Feb 9. - Much below normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Mon-Tue, Feb 8-Feb 9. 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