Extended Forecast Discussion NWS Weather Prediction Center College Park MD 348 PM EST Mon Jan 03 2022 Valid 12Z Thu Jan 06 2022 - 12Z Mon Jan 10 2022 ...Additional rounds of heavy coastal rain and mountain snow for the Northwest... ...Much below normal temperatures for the north-central U.S. and accumulating snow from the Appalachians to the Northeast late week... ...General Pattern Overview... The upper level pattern over the CONUS during the medium range period should remain fairly amplified but also progressive. Troughing sweeping through the East Thursday into Friday should give way to a brief period of upper ridging this weekend as an arctic air mass settles into the north-central U.S. in the wake of the strong cold front. Meanwhile, a strong atmospheric river may bring another round of heavy rain and mountain snows to the Northwest late this week with the upper trough sliding eastward into the Central U.S. and eventually the Great Lakes/Northeast and ridging beginning to build again over the West. Another trough may approach the West Coast by next Monday. ...Guidance assessment and uncertainty... The 00z/06z model guidance continues to show fairly good synoptic scale agreement through at least Saturday, with some lingering mesoscale timing and amplitude differences with individual shortwaves. Regarding the early period East Coast low, the 06z/12z GFS continues to be faster/more offshore with the track while the bulk of the rest of the guidance suggests something closer to the coast and a more impactful winter storm from the lower Ohio Valley into the Northeast. By Sunday, the 06z GFS was considerably stronger with a cut off upper low over the Southwest, which did not have much ensemble support, but it appears the 12z has backed off somewhat with that. By day 7, there are also some timing differences with the next system moving towards the West Coast. The WPC forecast was based primarily on a multi-deterministic model blend through Saturday. After this, the GFS was dropped due to the issues in the West described above, and contributions from the ensemble means were increased to account for growing late period uncertainties. This approach provided a relatively consistent forecast compared to the previous WPC blend. ...Sensible Weather... There will be multiple Pacific storm systems that will affect the Pacific Northwest and inland across portions of the Great Basin and the Northern Rockies. This will result in heavy rain and heavy mountain snow for Thursday and Friday, with a likely atmospheric river event for northern Oregon and southwest Washington during this time. A drying trend should commence in time for the weekend across much of the West as high pressure builds back into the region. Meanwhile, an area of accumulating snow is possible north and west of a low pressure system tracking across the Mid-Atlantic and deepening off the Northeast Coast Thursday-Friday. The latest guidance shows the best potential for at least a couple of inches across the central Appalachians/lower Ohio Valley into the northern Mid-Atlantic and New England. More showers and storms are likely to make a return to the Gulf Coast region and into the Tennessee Valley by Sunday ahead of the next front. Temperatures are expected to be much below normal across the central/northern Plains to the Upper Midwest through the end of the week with a large surface high of arctic origin governing the weather pattern for this region. Subzero highs are once again likely for portions of eastern Montana, North Dakota, and northern Minnesota, and highs in the teens settling as far south as Kansas on Thursday. Some moderation of the severe cold may come across this region on Saturday ahead of the next arctic surge into the northern tier states on Sunday, which is not expected to be as intense as the earlier arctic blast. Elsewhere, seasonably cold conditions are expected west of the Continental Divide with readings generally within 10 degrees of climatological averages, and mild across the southern Plains and Deep South with highs running 5 to 15 degrees above average this weekend. Santorelli/Hamrick 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 California, the Pacific Northwest, and the Northern Great Basin, Thu-Fri, Jan 6-Jan 7. - Heavy rain across portions of the Southeast, the Southern Appalachians, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Sat-Sun, Jan 8-Jan 9. - Heavy snow across portions of the Northeast, the Great Basin, the Tennessee Valley, the Northern Rockies, the Central Rockies, the Mid-Atlantic, the Southern Appalachians, the Central Appalachians, and the Ohio Valley, Thu-Fri, Jan 6-Jan 7. - Flooding possible across portions of the Pacific Northwest and the Ohio Valley. - Flooding occurring or imminent across portions of the Pacific Northwest and the Ohio Valley. - Much below normal temperatures across portions of the Northern/Central Plains, the Northern Rockies, the Upper/Middle Mississippi Valley, and the Upper Great Lakes, Thu-Fri, Jan 6-Jan 7. 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