Extended Forecast Discussion NWS Weather Prediction Center College Park MD 339 PM EST Mon Feb 15 2021 Valid 12Z Thu Feb 18 2021 - 12Z Mon Feb 22 2021 ...Much Below Normal Temperatures Across the Central U.S. Continue This Week... ...Another Storm System Expected for Deep South to Northeast and New England Later This Week... ...Pacific Northwest and Northern Rockies Becoming Unsettled Later This Week and This Weekend... ...Overview and Guidance Evaluation... A highly amplified upper level pattern across the CONUS to start the period will gradually flatten into this weekend though with shortwave energy coming in from the Pacific at times, some form of troughing is expected over the central U.S. during the whole period. Overall though, the Arctic blast and much below normal temperatures are forecast to moderate while attention turns to yet another deepening low forecast to track from the Gulf Coast toward the Mid-Atlantic and Northeast late this week, which could bring a variety of hazards including heavy rain, wintry mix, and heavy snow. Finally, a series of frontal passages and Pacific moisture for the Northwest into the Northern Rockies will keep the weather active with several opportunities for heavy mountain snow and lower elevation rain. In the large scale sense, the latest guidance showed very good agreement at 500 mb through the period with some of the typical timing differences evolving by day 5 through day 7. The exception was the UKMET which was a bit displaced with the Pacific Northwest to Northern Plains energy and also flatter compared to the slightly more amplified ECMWF/CMC/GFS. The GFS looked to be a bit too fast/ahead of the consensus and more agreeable CMC/ECMWF (tied closer to the ECENS mean) so for this cycle, the WPC blend incorporated mostly a ECMWF/GFS/CMC blend early on followed by a higher amount of the ECENS for day 6/7 to handle some of the forecast uncertainty. But overall forecast agreement was average to slightly above average for the synoptic pattern. ...Weather/Threats Highlights... A storm system is expected to evolve near the Gulf Coast then track up through the East Coast toward New England Thursday into Friday, bringing with it a variety of hazards including potential severe weather and heavy rainfall to portions of the Southeast. On the northern side of the system, interactions with a cold airmass in place and Canadian high pressure to the north will present a threat of snow and wintry mix from portions of the Arklatex through the Ohio Valley, Mid-Atlantic, and much of the Northeast and New England. Details on the transition zones between rain/wintry mix/snow will be fine-tuned as the event draws near but widespread travel impacts and hazardous conditions are possible. Behind this system, another couple fronts reaching the Northwest between Thursday and Saturday should bring the potential for additional focused rainfall along coastal portions of Washington/Oregon with heavy mountain snows in the Washington/Oregon Cascades and northern Rockies. Meaningful rain/high elevation snow may extend into parts of northern California as well. Temperatures will remain much below normal at the start of the period (Thursday) through about Saturday for much of the central U.S. and portions of the East Coast in the wake of the late week system. Departures from normal as much as 20-35F will be possible for some areas. Meanwhile, out West, slightly above normal temperatures are forecast for portions of the Southwest this weekend into early next week. South Florida and southern Arizona will be the warm spots throughout the whole period for the CONUS with daytime highs in the 70s to lower 80s. 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 snow across portions of the Great Lakes, the Northeast, the Central Appalachians, and the Ohio Valley, Thu-Fri, Feb 18-Feb 19. - Heavy precipitation across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Northeast, and the Ohio Valley, Thu-Fri, Feb 18-Feb 19. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, and the Southeast, Thu, Feb 18. - Severe weather across portions of the Southeast, Thu, Feb 18. - Flooding possible across portions of the Southeast, the Southern Appalachians, the Mid-Atlantic, the Central Appalachians, and the Ohio Valley. - Flooding occurring or imminent across portions of the Mid-Atlantic. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - Heavy precipitation across portions of California and the Pacific Northwest, Thu-Mon, Feb 18-Feb 22. - Heavy snow across portions of the Central Great Basin and California, Fri, Feb 19. - Heavy snow across portions of the Northern Great Basin, Thu-Fri, Feb 18-Feb 19 and Sun-Mon, Feb 21-Feb 22. - Heavy snow across portions of the Northern Rockies, Fri, Feb 19 and Sun-Mon, Feb 21-Feb 22. - High winds across portions of the Pacific Northwest, Sun, Feb 21. - High winds across portions of the Northern/Central Rockies and the Northern Plains, Sun-Mon, Feb 21-Feb 22. - Much below normal temperatures across portions of the Northern/Central/Southern Plains, the Upper/Middle/Lower Mississippi Valley, the Tennessee Valley, the Great Lakes, and the Ohio Valley, Thu-Sat, Feb 18-Feb 20. 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