Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Sat Feb 06 2021 Valid 12Z Tue Feb 09 2021 - 12Z Sat Feb 13 2021 ...Northern Plains to Midwest Arctic outbreak followed by possible northeast U.S. winter storm later next week... ...Pattern Overview and Guidance/Predictability Assessment... Models and ensembles still advertise a pattern favorable for extremely cold conditions persisting over the central U.S. through next week. However, there has been a general model trend for the arctic air mass to slow its expansion farther into the Deep South and the Southeast. Meanwhile, models have shown further adjustments in the way they handle the blocky synoptic pattern across Canada. The ECMWF has now trended toward the GFS by further retrograding the polar vortex westward into the Canadian prairies. These synoptic adjustments would tend to encourage further intrusion of Gulf moisture into the Deep South which would then be carried up the East Coast later next week along with a higher chance for cyclogenesis. The GFS has led the trend for more robust cyclogenesis over the Northeast later next week. On the other hand, the ECMWF tends to retain the cold air mass in place but the latest run (00Z) appears to agree better with the GFS in terms of the potential for late-week East Coast cyclogenesis. Elsewhere, the adjusted synoptic evolution also helps to develop a swath of mostly light snow to traverse the north-central U.S. during the latter part of next week in response to upper-level impulses exiting the central Rockies under the retrograding polar vortex in the Canadian prairies. Meanwhile, upslope snows will likely linger over the Colorado Rockies in the vicinity of the arctic front. The West will see more moderate temperatures but with a general cooling trend as the arctic air filters in from the north. Models have shown a slowing trend of the arctic front moving across the West. The WPC medium-range forecast package was derived from a composite blend of the 12Z ECMWF/EC mean, the 18Z GFS/GEFS, together with a smaller contribution from the 12Z CMC/CMC mean. Less of the GFS/GEFS was used on Days 6 and 7 when the 12Z NAEFS was used instead of the CMC mean. More of the ensemble means were used on Days 6 and 7 as well given the increasing model uncertainties. ...Weather/Threats Highlights... A band of meaningful snow is expected from the Midwest into the Northeast from Monday into Tuesday associated with a developing frontal wave, although details remain somewhat elusive. Meanwhile, a stationary front across southern Florida will lift northward and likely provide a period of enhanced rainfall from the eastern Gulf Coast region to the southeastern U.S. coast. By later next week, there is an increasing chance for Gulf moisture to return and expand in coverage across the southern tier states and possibly the East in an overrunning pattern north of a stationary front across the northern Gulf. Depending on details of upper flow there is also potential for this front/embedded wave(s) to lift farther northward over the East. With the cold air in place farther inland, a swath of wintry weather is possible from portions of the southern tier into the Northeast later next week but with lower confidence on the specifics. The forecast is fairly consistent in showing coldest anomalies of at least 20-30F below normal early in the week from the northern-central Plains into the Midwest, with some readings possibly as low as 30-45F below normal over parts of Montana. During the rest of the week this core of cold air will remain in place and steadily push to the south and east. Temperatures reaching 20-35F below normal may extend into the southern Plains and much of the Mississippi Valley by later in the week but uncertainty in the eastern U.S. pattern lowers confidence in exactly how cold the East will be at that time. Most locations west of the Rockies will see a general cooling trend. Northern areas should start out near to moderately below normal and trend a bit colder, while the Great Basin/Southwest start the weak moderately above normal and then decline toward normal (or slightly below in parts of the Great Basin). Kong/Rausch 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