Extended Forecast Discussion NWS Weather Prediction Center College Park MD 327 PM EST Mon Nov 14 2022 Valid 12Z Thu Nov 17 2022 - 12Z Mon Nov 21 2022 ***A vast portion of the lower 48 will have daily temperatures that resemble those of January rather than mid-November with widespread subfreezing maximum temperatures expected across the north-central states along with lake effect snow*** ...Synoptic Overview... A rather cold pattern is expected to be in place across much of the nation for the end of the week into next weekend with broad cyclonic flow aloft around a deep upper level trough centered near the north-central U.S. and extending to Hudson Bay. During this period, multiple cold fronts will sweep through the nation which will reinforce the chilly airmass. Additionally, a strong upper ridge axis should prevail just off the West Coast through Saturday before somewhat weakening. A well organized storm system will be crossing southeast Canada on Thursday, with coastal rain and inland snow expected, followed by lake effect snow downwind of the Great Lakes. ...Guidance and Predictability Assessment... The 06/12Z guidance overall has a good handle on the large scale pattern into the weekend that shows a strong reinforcement of the arctic air mass across much of the northern tier states. The global guidance and the ensemble means are fairly clustered for the Great Lakes region, at least through the middle of the extended. There is still a signal for a storm to develop near the Southeast Coast which is depicted as a weaker system at this time. This equates to a lower potential for precipitation to advance much inland. The WPC forecast was primarily based on a multi-deterministic model blend through into the weekend with increasing the inclusion and weighting of the GEFS and EC ensemble means to account for the greater model differences for the weekend and beyond. For the QPF forecast, particularly for and in the vicinity of the Great Lakes, the NBM 4.0 solution was too light given the setup for the lake enhanced precipitation so trended toward the CMC, ECWMF, and ensemble means to increase values. ...Weather/Hazard Highlights... A vast area covering the northern and central states will have below seasonal average temperatures for mid-November through most of the extended period. Some locations across the Northern High Plains are forecast to have daily highs only climbing into in the low teens with overnight lows dipping below zero. Some record low temperatures are possible across western reaches of the High Plains, and some record low maximums are also possible across portions of the Central Plains to the Upper Midwest behind the next surge of arctic air. Chilly temperatures will reach the Gulf Coast and even much of the Florida Peninsula for at least the first half of the forecast period, with highs generally running 10-20 degrees below mid-November average. By early next week there may be some warming back to near seasonal temperatures. Most of the country will be relatively dry precipitation-wise given the pattern. Lake effect snow will likely persist downwind of the Great Lakes owing to strong cold air advection over the warmer waters, with the heaviest snow expected east of Lake Erie and Lake Ontario. Some snow showers are also likely across portions of the Rockies as a weak disturbance drops southeastward, but nothing major expected there. There is a bit more uncertainty regarding the potential evolution and track of a wave of low pressure over the Gulf that could bring light to moderate rain for the Gulf Coast region and the interior Southeast by the weekend, so this will continue to be closely monitored. Campbell 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 Hazards: - Flooding occurring or imminent across portions of the Southeast. - Flooding likely across portions of the Southeast. - Much below normal temperatures across portions of the Northern Plains/Rockies, the Upper Mississippi Valley, and the Great Lakes, Thu-Mon, Nov 17-Nov 21. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml