Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Wed Dec 1 2021 Valid 12Z Sat Dec 4 2021 - 12Z Wed Dec 8 2021 ...Overview... A quasi-zonal flow pattern is expected to be in place to begin the weekend across the northern tier states with a broad trough over the Great Lakes and Northeast, and an upper ridge over the Intermountain West with an upper low southwest of California. There will likely be two organized storm systems to contend with through the middle of next week, with the first tracking from the Midwest to the Northeast through Monday, and the second one tracking from the central Rockies to the Ohio Valley and Mid-South by Wednesday. ...Guidance/Predictability Assessment... The 00Z model guidance suite is in decent agreement on Saturday before more noticeable differences emerge by Monday, with the GFS indicating a faster shortwave passing through the Pacific Northwest compared to the model consensus, and slightly more amplified with the trough over the Great Lakes. By the end of the forecast period, there is a bit of model spread with the upper low over northwestern Mexico, but this is not expected to be impactful in terms of sensible weather. There are still timing and amplitude differences with the second storm system crossing the central U.S. by the middle of the week, and the ensemble means provided a good starting point for placement. The WPC forecast was primarily based on a CMC/ECMWF/GFS blend through Sunday. Thereafter, increased weighting towards the ensemble means whilst keeping some of the operational GFS and ECMWF and some previous WPC continuity. ...Weather/Hazards Highlights... Rounds of light to moderate precipitation are forecast for the Midwest, Great Lakes, and Northeast with a progressive storm track over the region through Monday, with snow expected to be the main precip type over the northern Great Lakes and northern New England. Moisture increasing ahead of the cold front is expected to result in scattered showers and a few thunderstorms from the Deep South to the Ohio Valley over the weekend, but amounts are not currently expected to be excessive. A shortwave and cold front reaching the Pacific Northwest by Sunday night and through Monday is expected to result in another round of moderate to locally heavy rain and mountain snows to western Washington and Oregon, with some of this moisture reaching the northern Rockies by Tuesday with heavy snow possible for the higher elevations of northern Idaho, western Montana, and western Wyoming. By the end of the forecast period next Wednesday, additional showers and some storms are likely to develop ahead of a second cold front crossing the Mississippi River valley. Temperatures are expected to be above normal for early December across most of the nation through early next week, with the greatest positive anomalies expected for western High Plains on Saturday where highs are forecast to be 15 to 20 degrees above average. Another episode of well above normal temperatures is likely for parts of Texas and Oklahoma on Tuesday ahead of the next cold front. On the other end of the spectrum, cold weather is forecast to continue across the Northeast U.S. with highs running up to 10 degrees below normal through the weekend with a cold upper level trough overhead. However, no major arctic airmass intrusions are expected during this forecast period. 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 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