Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Tue Nov 30 2021 Valid 12Z Fri Dec 3 2021 - 12Z Tue Dec 7 2021 ...Overview... A quasi-zonal flow pattern is expected to be in place to close out the work week across the northern tier states with a pronounced trough exiting the East Coast. By the weekend, an upper ridge axis tries to become established over the West Coast and the eastern Pacific, and a trough amplifies with developing surface low over the Plains. This will likely be followed by a second well organized storm system by the end of the forecast period across the western High Plains, with a zonal flow pattern across the eastern half of the nation. ...Guidance/Predictability Assessment... The 00Z model guidance suite is in decent agreement on Friday before more noticeable differences emerge by Saturday, with the GFS indicating a flatter trough over the Great Lakes and Northeast, and the ensemble means are not capturing the magnitude of the incoming trough across the Pacific Northwest that will eventually lead to an organized low pressure system over the Plains by Sunday morning. The CMC has trended more in line with the model consensus compared to previous days across the western U.S., and is reasonably close to the GFS and ECMWF with portraying the next trough/storm system arriving on the West Coast by Monday night. By the end of the forecast period, the GFS is considerably stronger and slower with the trough approaching the East Coast. The WPC forecast was primarily based on a CMC/ECMWF/GFS blend through Saturday. Thereafter, increased weighting towards the ensemble means whilst keeping some of the operational GFS and ECMWF. ...Weather/Hazards Highlights... Weather should be relatively uneventful in terms of rainfall or snow related hazards with not much in the way of heavy precipitation currently expected through early Sunday. Rounds of relatively light precipitation are forecast for the Midwest, Great Lakes, and Northeast with a progressive storm track over the region. Moisture increasing ahead of a 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. 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 the central and southern Plains on Friday where highs are forecast to be 15 to 25 degrees above average. Another episode of well above normal temperatures is likely for the western High Plains on Monday ahead of the next cold front. A few locations may approach daily record highs with these mild temperatures. 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