Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 AM EST Sun Nov 28 2021 Valid 12Z Wed Dec 1 2021 - 12Z Sun Dec 5 2021 ...Overview... The overall pattern will be featured by an upper level ridge from the eastern Pacific to the Intermountain West, and quasi-zonal flow from the Plains to the East Coast with multiple shortwave perturbations pivoting around a synoptic scale trough over southeast Canada. This will include an organized low pressure system tracking across southern Canada through Friday with a trailing front followed by a weaker low this weekend. By next Sunday, another storm system may develop across the Plains along a strong frontal boundary. ...Guidance/Predictability Assessment... The 00Z model guidance suite begins the period on Wednesday with average levels of agreement and then below average forecast confidence for late week and beyond. Recent GFS runs have been quite varied regarding a southern stream shortwave crossing the Gulf Coast region late in the week, with limited support from the ensemble means. There has also been a fair amount of model run-to-run variability with the ECMWF as well across the Great Lakes region and the degree of northern stream trough amplitude. Towards the end of the forecast period, the CMC is much stronger with an East Coast trough, although not as impressive as its 12Z run. There is also a high degree of model spread along the West Coast by next weekend owing to a disorganized flow pattern over the northeast Pacific and potential weakening of the upper ridge axis. The WPC forecast was primarily derived from the 12Z GFS/ECMWF/UKMET for Wednesday and Thursday, and then more of the GEFS/EC means thereafter while maintaining 20-30 percent of the previous WPC forecast for pressures in order to maintain good continuity. ...Weather/Hazards Highlights... Things should be relatively quiet in terms of rainfall or snow related hazards with not much in the way of heavy precipitation currently expected. The active pattern favoring atmospheric rivers over Washington state in the short-range period is expected to abate by Thursday as a surface high builds over the Pacific Northwest and British Columbia. Light to moderate rain is likely from the Great Lakes to the Northeast through mid-week owing to the progressive storm system near the U.S./Canada border, followed by some lake effect rain/snow showers to close out the week. Depending on the eventual strength and location of a potential organized low pressure system over the Plains next week, showers and some thunderstorms will be possible from the Gulf Coast to the Midwest. Temperatures are expected to be well above normal for this time of year across the Western U.S. and the Plains through the end of the week owing to the ridge aloft, and closer to normal for the East Coast on Wednesday followed by a warming trend for Thursday and Friday. Both highs and lows are forecast to be 15 to 25+ degrees above average for northern and central portions of the High Plains and expanding into the Midwest for Wednesday and Thursday. A few locations may approach daily maximum and minimum temperature records with these mild temperatures. However, it is worth noting that substantial changes to the forecast are possible going forward given the uncertainties noted in recent model runs. 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