Extended Forecast Discussion NWS Weather Prediction Center College Park MD 126 AM EST Wed Dec 29 2021 Valid 12Z Sat Jan 01 2022 - 12Z Wed Jan 05 2022 ...Bitterly Cold Temperatures to continue into New Year's Day across the Northern Rockies/Plains... ...Heavy New Year's Day Heavy Snows Threat for the south-central Great Basin/Rockies... ...Heavy Rain/Convection threat from the Mid-South/Ohio Valley to the Mid-Atlantic/Southeast New Year's Eve into New Year's Day... ...Backside Heavy Snow threat meanwhile shifts from the Central Plains and Midwest/Great Lakes/Northeast down through the southern Appalachians... ...Multi-day Heavy rain and terrain snow threat Sunday-Tuesday from the Northwest to North-Central California... ...Guidance and Predictability Assessment... The WPC model blend was comprised of equal parts of the 12Z ECWMF/EC ensemble mean/CMC/GEFS mean as they continued to have similar pattern evolution and maintained continuity with the previous forecast. The synoptic pattern for the extended period are still showing above average predictability. The composite blend tends to mitigate small-moderate scales timing and phasing differences with embedded systems that remains an issue that increases local focus uncertainty. ...Weather/Hazards Highlights... A series of shortwaves will dig through the amplified ridge over the east-central Pacific Ocean; which will send frontal systems into the West Friday into Saturday in addition to cold temperatures across the south-central Great Basin and Rockies with locally enhanced snowfall. Ejecting upper trough energies in two streams out from the West will generate systems and enhance an emerging east-central U.S. precipitation focus with progression out across the central and eastern U.S. as an upper ridge erodes over the Southeast. Deep moisture streaming into the frontal system over the central/south-central portion of the country will lead to heavy rainfall and localized runoff. Flooding concerns may be elevated especially across the Mid-South and Ohio Valley/Northeast to ring in the new year. Some of these storms across this region may also be severe, per SPC. Colder air will filter into the central U.S. causing temperatures to significantly drop and will also spread the risk for heavy snow from the Central Plains to the Great Lakes region. Wavy frontal progression should shift organized rains more into the Mid-Atlantic/Southeast into Sunday before working offshore. With the colder air making its way toward the Appalachians, lingering Sunday snow/ice chances from the southern Appalachians and vicinity up through the Northeast may be possible. Sunday-Tuesday of next week will be active for a majority of the Pacific Northwest and the north-central parts of California as the upper level pattern transitions as part of a developing Omega block over the Northeast Pacific in the form of a deeply amplified closed upper low/trough digs slowly southward from the Gulf of Alaska to offshore the Northwest. This will result in a windy and heavy precipitation couple of days. Moderate to heavy coastal rains and heavy mountain snows inland from the Cascades to the Sierra can be expected. 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: - Heavy precipitation across portions of California, the Great Basin, and the Pacific Northwest, Sun-Tue, Jan 2-Jan 4. - Heavy precipitation across portions of the Northeast and the Great Lakes, Sat, Jan 1. - Heavy precipitation across portions of the Southwest, Fri, Dec 31. - Heavy rain across portions of the Central/Southern Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southeast, and the Ohio Valley, Sat-Sun, Jan 1-Jan 2. - Heavy snow across portions of the Central/Southern Rockies, the Central Great Basin, the Central Plains, and the Southwest, Fri, Dec 31. - Heavy snow across portions of the Great Lakes and the Upper Mississippi Valley, Sat, Jan 1. - Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Fri, Dec 31. - Severe weather across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southeast, and the Ohio Valley, Sat, Jan 1. - Much below normal temperatures across portions of the Upper Mississippi Valley, the Pacific Northwest, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Fri-Sat, Dec 31-Jan 1. - Much below normal temperatures across portions of the Northern/Central Plains, the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley, Sat-Sun, Jan 1-Jan 2. 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