Extended Forecast Discussion NWS Weather Prediction Center College Park MD 151 AM EST Sat Jan 02 2021 Valid 12Z Tue Jan 05 2021 - 12Z Sat Jan 09 2021 ...Weather Pattern Overview... Quasi-progressive flow over the western 2/3rds of the CONUS will maintain a stormy pattern over at least the Pacific Northwest through the week. Over the East/Northeast, downstream blocking over the northern Atlantic (Labrador Sea) will stall a system just off New England early in the period until a trailing upper low merges into it and ultimately pushes it eastward. Pacific system will trek eastward out of the central Plains to the East Coast Wed-Fri with uncertainty as it may then lift northeastward along the coast or continue out to sea. Relatively mild Pacific air will dominate the lower 48 through the week, keeping arctic air in Canada. ...Guidance/Predictability Assessment... With a relatively complicated pattern comprised of shorter wavelength western features and merging eastern features, a blended solution again offered a reasonable starting point. 12Z ECMWF was a bit better clustered with the ensemble means, though they diverged in timing over the West by around next Thu-Fri. However, used more deterministic model weight than normal for this uncertainty as to not wash out the features that at least maintain good continuity considering the pattern. ...Weather/Threats Highlights... An area of low pressure lingering near/off New England early Tuesday will bring at least some light to modest precipitation to eastern New England depending on its proximity to the coast and structure. A slow exodus could prolong oceanic affects at the least, but perhaps remain a coastal threat as well. The Pacific Northwest will see the brunt of the precipitation next week with a string of systems, about one every other day, coming ashore. Multi-day precipitation totals could exceed several inches in many areas (even lower elevations west of the Cascades) with considerable snowfall in the Cascades. Expect windy conditions and variable snow levels (though not too low) as the systems move through. By later in the week, low pressure in the Southern Plains moving eastward will promote an area of expanding rain and perhaps some snow on the north side of the system in the marginally cold air mass. Temperatures will be well above normal along the Canadian border by about 10-20 degrees, especially for overnight lows, through next week. Modestly above normal temperatures can be expected for most of the rest of the CONUS east of the Rockies and north of the Southeast. The exception area could be the east-central states depending on the low track and intensity of the main wave of concern crossing the CONUS next week. The interior West should see near to slightly below normal temperatures in the active pattern. Fracasso 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