Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 AM EST Thu Dec 2 2021 Valid 12Z Sun Dec 5 2021 - 12Z Thu Dec 9 2021 ...Overview... The overall upper level pattern is forecast to transition from quasi-zonal to more amplified, with the western U.S. upper ridge becoming established farther west over the eastern Pacific and multiple troughs passing over the Plains and Midwest. 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 late Monday, and the second one tracking from the central Rockies to the Ohio Valley and Mid-South by midweek. An Alberta clipper-type system may affect the Northern Plains by next Thursday. ...Guidance/Predictability Assessment... There has been an overall improvement in the consolidation of the 00Z model guidance compared to recent days as the overall pattern becomes more amplified, with forecast confidence now average compared to below average in recent days. With the first storm system crossing the Great Lakes/Northeast through Monday, the GFS was faster and farther north than the model consensus, including its own ensemble mean, so it was not favored through early Tuesday. The character of the next shortwave nearing the Northwest early next week will depend on how much if any interaction there may be between northern stream energy just south of Alaska and a separate upper low farther south, with no clear consensus evident yet for exactly what will happen. This leads to noteworthy model differences, with the GFS initially quite strong with the shortwave and faster, and the CMC is considerably slower and farther west, and a good deal of spread among individual ensemble members. The CMC is also farther east than the consensus with the upper low near northwest Mexico, but this does not appear to have a significant impact on sensible weather at this time. The first half of the forecast incorporated the ECMWF/CMC/UKMET and some of the ECENS, with the GFS excluded due to the reasons previously mentioned. However, the GFS was slightly more in line with the overall pattern by late in the period, so it was substituted for the CMC along with more of the ensemble means. ...Weather/Hazards Highlights... There is the potential for a band of light to moderate snow from northern Michigan to northern New England through Monday as an organized storm system passes through the region. Precipitation type and intensity over the eastern Great lakes and New England will depend on the exact low track. 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 through Monday morning. There could be some locally moderate to heavy rain embedded within this area but with fairly low confidence regarding exact placement. The shortwave and cold front forecast to reach the Pacific Northwest by Sunday night and through Monday should produce a period of moderate to locally heavy rain and mountain snows over western Washington and Oregon, with some of this moisture reaching the northern Rockies by Tuesday. Heavy snow will be possible for the higher elevations of northern Idaho, western Montana, and western Wyoming. In addition, some moisture will likely extend farther south over favored terrain in the Great Basin and central Rockies. By the Wednesday-Thursday time period, more rainfall is likely for the east-central U.S. ahead of this same storm system, and wintry precipitation farther north across the Great Lakes and New England. Temperatures are expected to be near to above normal for early December across most of the nation through the early to middle of next week, with the greatest positive anomalies expected for western portions 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, and another round of below average readings on Tuesday along the East Coast which should moderate by Wednesday. 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