Extended Forecast Discussion NWS Weather Prediction Center College Park MD 218 PM EST Tue Nov 15 2022 Valid 12Z Fri Nov 18 2022 - 12Z Tue Nov 22 2022 ***Persistent Lake Effect Snow to impact the shorelines and favored downwind locations, especially for Lakes Erie and Ontario where significant snowfall will be particularly hazardous*** ***Very cold temperature to continue across much of the nation this weekend with widespread subfreezing maximum temperatures expected across the north-central states*** ...Synoptic Overview... A highly amplified upper level flow pattern will be in place across the country for the end of the work week with a deep trough extending from Hudson Bay to the Midwest states. An arctic front is progged to reinforce the already very cold airmass that will be in place across the north-central U.S. that is forecast to reach the East Coast in time for the weekend. This trough and accompanying January-like temperatures will likely have some staying power until early next week, when there are signs of a pattern change emerging. The deep trough will likely begin lifting out as a more zonal flow pattern commences across much of the country. Out West, a pacific storm system will likely move inland as the upper ridge axis decays by Sunday and into Monday. ...Guidance and Predictability Assessment... The global guidance and their ensemble means are in very good agreement with the broad upper-level trough that will be tracking through the central and eastern states will above average confidence through much of the extended period. Multiple surges of cold air will reinforce the below seasonal average temperatures and keep lake enhanced precipitation to the Great Lakes region and surrounding locations. The models also agree well on said trough lifting out starting Monday and heralding a pattern change. The greatest model differences are apparent across the Western U.S. going into early next week as a Pacific shortwave approaches the central-northern West Coast region. The CMC is considerably weaker than the GFS/ECMWF for the system reaching the coast Monday, although the CMC shows a stronger shortwave following behind it that is not reflected much in the other guidance. The WPC forecast was primarily based on a multi-deterministic model blend through the weekend, with a gradual increase in use of the EC and GEFS means going into the first part of the week. For the QPF forecast, particularly 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 more toward the CMC regional and ECWMF to increase values. ...Weather/Hazard Highlights... Chilly air will be in place for a large portion of nation through the weekend and into the upcoming week. Some of the coldest air will be centered over the north-central U.S. where the daily maximums will struggle to reach the 10s and overnight lows -/+ 5 degrees from zero. Some record low temperatures are also possible across portions of the Northern Plains and Midwest, 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 also 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 5 to 15 degrees below mid-November averages. Temperatures will trend less cold as the deep upper trough begins lifting out with a more zonal flow evolving. In terms of precipitation, much of the nation should be relatively dry as a sprawling surface high governs the overall weather pattern. Lake effect snow is likely to be persistent downwind of the Great Lakes through Sunday owing to strong cold air advection over the warmer waters, with the heaviest snow expected east of Lake Erie and Lake Ontario where over a foot of accumulation is possible. This early season, heavy and wet snow may led to very hazardous traveling conditions and potentially have significant impacts to structures, trees and power lines. Showers and mountain snow are likely to make a return to the West Coast states early next week as the Pacific storm system moves inland. Campbell/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, 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