Extended Forecast Discussion NWS Weather Prediction Center College Park MD 241 AM EST Wed Dec 21 2022 Valid 12Z Sat Dec 24 2022 - 12Z Wed Dec 28 2022 ***A major winter storm exiting into eastern Canada will likely continue to cause strong winds on Saturday near the Great Lakes, along with bitterly cold temperatures for Christmas weekend*** ...Synoptic Overview... After an extremely impactful winter storm hammers the Eastern U.S. during the short range period, things start to improve going into Christmas weekend as the core of the low lifts northward across Quebec and then Hudson Bay. However, it will still be quite windy across the Great Lakes region and the Northeast on Saturday with a strong pressure gradient still in place, along with some lake effect snow. The impressively cold airmass will begin modifying as the surface high settles across the southern tier states. Looking ahead to early next week, an Alberta clipper system tracks across the central/northern Plains, and a southern stream disturbance tracks eastward near the Gulf Coast. Multiple shortwave passages near the Pacific Northwest will keep things unsettled from northern California to Washington state. ...Guidance/Predictability Assessment... The latest 00Z model guidance suite indicates very good synoptic scale agreement this weekend on the overall upper level pattern that features a West Coast ridge and a potent eastern U.S. trough, with Pacific shortwaves rounding the ridge and feeding into the mean trough. Attention turns to the Plains and then the Gulf Coast region as two distinct shortwaves track down the east side of that ridge, but right now the guidance does not indicate any appreciable phasing of these disturbances through Monday, so this would limit the potential for any coastal surface low trying to develop near the Southeast U.S. but still worth monitoring. By the end of the forecast period on Wednesday, the 00Z ECMWF is much stronger with a closed low near the Great Lakes, and the GFS stronger with the trough exiting the East Coast, and there are more significant timing differences over the Pacific Northwest, so more of an ensemble mean approach works well by Tuesday into Wednesday. ...Weather/Hazard Highlights... The departing winter storm is still likely to produce strong and potentially damaging winds from Michigan to Upstate New York through the day Saturday before gradually abating by Saturday night. Intense cold air advection over the warmer lake waters is expected to produce bands of lake effect/enhanced snow, some of which could be locally heavy. Frigid wind chills will also be a harsh reality from the Midwest to the Ohio/Tennessee Valley, and then extending eastward to the East Coast whilst not quite as severe as locations west of the Appalachians. The widespread snow from earlier in the event is expected to produce a white Christmas for many locations. Widespread anomalies on the order of 20-30 degrees below average for highs and 15-25 degrees for lows are expected for most locations in the central and eastern U.S. on Saturday, and things will improve going into Monday with highs 10-20 degrees below average, and then returning closer to average by the middle of next week, and slightly above average for the Rockies and extending to the East Coast. A multi-day heavy precipitation event is becoming more likely for the West Coast as a couple of potential atmospheric river events advect copious moisture inland from the Sierra to the Cascades, with the highest totals appearing likely Monday night and into Tuesday with several inches of rain and a few feet of snow at the highest elevations. Showers may also increase in coverage across parts of Florida on Tuesday near the developing coastal frontal boundary. 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