Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 AM EST Mon Nov 29 2021 Valid 12Z Thu Dec 2 2021 - 12Z Mon Dec 6 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 to low amplitude troughing 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 southeastern Canada through Friday with a trailing front followed by a weaker low this weekend, leading to rounds of mainly light precipitation across the Great Lakes and northeastern U.S. By the weekend, showers and some storms are likely to develop ahead of a developing storm system from the Gulf Coast to the Ohio Valley. ...Guidance/Predictability Assessment... The 00Z guidance suite is in decent synoptic scale agreement through Friday with an upper ridge over the southwestern U.S. and a broad trough over the Northeast U.S. As the flow pattern becomes more quasi-zonal by Friday night and into the weekend, model spread increases with respect to the next shortwave trough entering the northwestern U.S., as well as a weak southern stream upper low developing over northern Mexico, and overall forecast confidence is below average for this time period owing to significant run-to-run model variations. Some of the greatest model differences are with the past few runs of the CMC that have been out of phase along the West Coast for the end of the forecast period and qualify as outlier solutions compared to ensemble spaghetti plots for days 6 and 7. Therefore, the WPC forecast was primarily based on a GFS/ECMWF/UKMET blend through Friday, and then mainly ensemble means with some operational GFS/ECMWF and some previous WPC continuity. ...Weather/Hazards Highlights... Weather should be relatively quiet in terms of rainfall or snow related hazards with not much in the way of heavy precipitation currently expected through Saturday. Rounds of relatively light precipitation are forecast for the Midwest, Great Lakes, and Northeast with a progressive storm track over the area. Amounts should be most substantial in favored lake effect and possibly upslope areas, particularly downwind of Lake Ontario into the Adirondacks. Then moisture is set to increase across the Southern Plains and Lower Mississippi Valley late Friday and into the weekend, which could lead to showers and thunderstorms becoming more widespread there and then extending northeastward as the surface low over the Great Lakes becomes better organized. Temperatures are expected to be above normal for this time of year across most of the nation through next weekend, with the greatest positive anomalies expected for the central and northern Plains where both highs and lows are forecast to be 15 to 25+ degrees above average for late in the week. A few locations may approach daily maximum and minimum temperature records with these mild temperatures. By the weekend, temperatures are currently forecast to moderate somewhat, but this is subject to change given forecast uncertainties. No 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