Extended Forecast Discussion NWS Weather Prediction Center College Park MD 522 PM EST Tue Feb 09 2021 Valid 12Z Fri Feb 12 2021 - 12Z Tue Feb 16 2021 ...Arctic air extends across the Northern Rockies and Plains, Surging South across the Plains and MS Valley, with multiple cold temperature records expected... ...Mixed precipitation events possible for the mid-lower MS Valley to the Ohio Valley... Appalachians...Mid-Atlantic...and Northeast... A large area of arctic air with strong high pressure emerges from the northern Rockies and high Plains on Day 3 and moves east across the Plains late this week, with cold air then surging south across the Plains and MS Valley through the weekend. Several potential records for lowest maximum temperatures are possible later this week, and both high and low minimum temperature records over the MS Valley this weekend to early next week. Current forecasts indicate dozens of low temperature records are possible Sun 13 Feb and Mon 14 Feb across the central to southern Plains east to the mid and lower MS Valley. High temperature anomalies of 30-45F below normal are forecast across the northern to central Plains Days 4/ Saturday and Day 5/Sunday. The airmass gradually moderates early next week. Global models indicate a polar vortex centered in south central Canada Fri will begin to weaken and slide eastward across the Great Lakes by this weekend. On the other hand, the 00-12z GFS depicts shortwave energy rotates through the south side of the polar vortex, resulting in frontal wave development in the Great Lakes during the weekend. The 00z ECMWF/CMC solutions are preferred given the GEFS mean was more progressive than the operational GFS with the vortex movement, as well as better agreement with WPC continuity. A pair of upper shortwaves move onshore in CA and moves across the southwest, bringing rounds of valley showers/mountain snow. The first 500 mb wave is forecast to weaken in confluent flow as it ejects onto the Plains. The second wave crossing the Southwest Sun 14 Feb moves east across the southern Plains Mon and MS Valley Tue. 16 Feb., leading to low pressure development in the Gulf Of Mexico that produces a large swath of mixed precipitation across the mid-lower MS Valley, Ohio Valley, and Appalachians. The 12z UKMET/12z GFS were faster than the 06z GFS/00z ECMWF and their respective ensemble means with the trough progression across the southwest and southern Plains, so were given the last weighting. The models continue to signal periods of snow on Days 4-5 across the ranges of WA/OR, southern ID, WY, northern CA, northern NV and UT. On Day 6, the southwest trough is forecast to produce snows in the ranges of AZ/UT/NM/CO. On Day 7, snows wind down in the southern Rockies and then redevelop in the mountains of western WA/OR as the next system approaches from the northeast Pacific Ocean. The WPC medium-range forecasts were derived from a blend of the 00Z ECMWF/ECMWF Ensemble mean with less weighting on the 00z Canadian global/00z CMC Ensemble mean. Petersen/Kong 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 Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Tue, Feb 16. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Northeast, Tue, Feb 16. - Heavy rain across portions of the Southeast, Mon, Feb 15. - Heavy snow across portions of California, the Pacific Northwest, and the Northern Great Basin, Fri-Sat, Feb 12-Feb 13 and Mon, Feb 15. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat, Feb 13. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Rockies, the Southern Rockies, the Northern Great Basin, and the Southwest, Fri, Feb 12. - Heavy snow across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Mon, Feb 15. - Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Sat-Sun, Feb 13-Feb 14. - Much below normal temperatures across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Fri-Sun, Feb 12-Feb 14. - Much below normal temperatures across portions of the Plains, the Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Great Lakes, the Northern/Central Rockies, the Southeast, and the Ohio Valley, Fri-Tue, Feb 12-Feb 16. - Much below normal temperatures across portions of the Northeast, the Central/Southern Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southeast, the Great Lakes, and the Ohio Valley, Mon-Tue, Feb 15-Feb 16. 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