Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 AM EST Sat Jan 1 2022 Valid 12Z Tue Jan 4 2022 - 12Z Sat Jan 8 2022 ...Multi-day coastal heavy rain and mountain focusing heavy snow threat for the Pacific Northwest and northern California to the northern Great Basin/Rockies next week... ...Arctic blast to focus over the north-central U.S. Tuesday-Friday with snow likely for the Great Lakes states through the interior Northeast... ...Weather Pattern Overview... A cold Canadian surface high will be in place across the eastern U.S. on Tuesday in the wake of the strong cold front that will be exiting the East Coast for the beginning of the week. Surface cyclogenesis ensues over the Northern Plains in response to an amplifying upper trough, and another surge of arctic air behind it. A potentially strong low pressure system is on the horizon to close out the week across the East Coast, and multiple disturbances also take aim at the Pacific Northwest with an atmospheric river event likely for portions of northern California and southern Oregon. ...Guidance/Predictability Assessment... The 00z model guidance suite appears to be in above average agreement on the synoptic scale with more differences noted in mesoscale features regarding the low pressure systems expected to affect the continental U.S. through the middle of the week. The 12Z UKMET strayed from the model consensus as early as Tuesday night and even more so by Wednesday and Thursday across the Great Lakes region, but the 00Z is more in line with the ECMWF/CMC/GEFS mean. The 00Z GFS is a bit south of the ensemble means with the low crossing the Great Lakes Wednesday with a sharper shortwave trough axis. Regarding the next system, the CMC/GFS are favoring a faster solution than the ECMWF. The greatest model uncertainties are evident over the eastern Pacific and West Coast region by Friday and into Saturday with both northern and southern stream shortwave energy breaking down the western U.S. ridge by that time. Taking these factors into account, the WPC forecast was primarily based on a CMC/ECMWF/GFS blend through early Thursday, and then ECMWF/GFS/some CMC with gradually increasing use of the GEFS/ECENS for Friday and Saturday. ...Sensible Weather and Hazards... Heavy coastal rain and heavy mountain snow is expected from northern California to western Washington for early to middle part of the week as a storm system moves inland across the Pacific Northwest, likely the result of an atmospheric river event. This moisture is expected to reach the central and northern Rockies with heavy snow, mainly on Wednesday and Thursday. Unlike recent events, this storm is not currently expected to produce heavy precipitation for central/southern California. The surface low over the north-central U.S. for Tuesday-Wednesday will likely have a swath of light to moderate snow, and lake enhanced snow across much of Michigan with some blowing/drifting snow as winds increase with the arctic airmass moving into the region. Depending on what happens along the East Coast late in the week, moderate to locally heavy rain for the Southeast U.S. and snow for the Appalachians and portions of the Ohio Valley can be expected. In the temperature department, there will be a return to seasonably cold conditions across much of the Deep South and the East Coast for early in the week after days of well above average temperatures and humidity levels. There is likely a brief moderation across the Plains and Midwest states on Tuesday ahead of the next arctic front, which will herald a return to frigid conditions across the Northern Plains and Upper Midwest by Wednesday and beyond, with highs running a good 15-30 degrees below seasonal averages in many cases. Portions of Montana may be up to 40 degrees below normal by Wednesday! This will equate to subzero high temperatures once again across portions of northern Montana, North Dakota, and northern Minnesota, with a few record lows possible. Wind chills will also reach hazardous levels for these same areas, and wind chill related weather bulletins will likely be needed for much of the north-central U.S. as the arctic airmass settles into the region. The good news is the severity of the cold should moderate quite a bit by the time this airmass reaches the East Coast, but still 5-15 degrees below average by the end of the week for many areas. Out West, readings are likely to be within 10 degrees either side of average for most areas next week west of the continental divide. 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