Extended Forecast Discussion NWS Weather Prediction Center College Park MD 125 PM EST Sat Feb 06 2021 Valid 12Z Tue Feb 09 2021 - 12Z Sat Feb 13 2021 ...Frigid Arctic Air Persists for Northern Plains And Upper Midwest... ...Possible Mid-Atlantic to Northeast U.S. Winter Storm Later Next Week... ...Pattern Overview and Guidance/Predictability Assessment... The latest suite of deterministic and ensemble guidance shows the blocky upper level pattern remaining mostly in place through the place, with the main feature being the slowly retrograding polar vortex into the Canadian prairies, which is well agreed upon by the models through day 5. Its slow southward and southeastward sag by day 6/7 is more uncertain. At the surface, this setup favors more Gulf moisture to stream northeastward along the East Coast in the quasi-southwest flow aloft with favorable setup for cyclogenesis, which is depicted somewhat by all the various global models. While the ingredients are there, deterministic runs of the ECMWF/CMC/GFS vary widely with the track and position of cold air in place so the sensible weather details are far from certain. 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 00Z ECMWF/EC mean, the 06Z GFS/GEFS, together with a smaller contribution from the 00Z CMC/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 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. A quick moving shortwave impulse tracking from the lower Ohio Valley into the central Appalachians could bring some meaningful accumulations of snow to the favored terrain areas of eastern Kentucky and West Virginia. The latest winter weather outlook probabilities have increased there this cycle. Later next week, Gulf moisture is forecast 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 remains possible from portions of the southern tier into the Northeast later next week but with lower confidence on the specifics. The latest Winter Weather Outlook probabilities for snow show 30-50 percent chances from southern VA to New England. 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/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 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