Extended Forecast Discussion NWS Weather Prediction Center College Park MD 153 AM EST Sun Jan 2 2022 Valid 12Z Wed Jan 5 2022 - 12Z Sun Jan 9 2022 ...Additional rounds of heavy coastal rain and mountain snow for the northwestern states... ...Frigid air mass for the north-central U.S. and potential snow for inland portions of the East Coast region late in the week... ...General Pattern Overview... The upper level flow pattern over the nation will be rather amplified through the end of the week with a large scale trough over the east-central U.S. and a broad ridge over the West Coast, before transitioning to a more quasi-zonal flow by next weekend. Two well defined low pressure systems are expected to affect the Great Lakes region and also the East Coast, and a third system is possible by next weekend across the Plains and Midwest. An arctic air mass will settle southward across much of the north-central U.S. in the wake of the strong cold front. ...Guidance assessment and uncertainty... The 00Z model guidance suite is in excellent synoptic scale agreement through the majority of the forecast period with some mesoscale timing and amplitude differences with the individual shortwave passages. These minor differences are all within the ensemble spread for the most part. By Friday with the East Coast system, the 00Z GFS is slightly farther offshore with the track of the low and thus would be less impactful in terms of rain/snow across the Northeast. The CMC becomes faster with the shortwave crossing the Plains by Saturday and also more amplified across the Southeast, whereas the ECMWF/GFS suggest a flatter mid-upper flow pattern here. The WPC forecast was based primarily on a multi-deterministic model blend through Thursday, and then GFS/ECMWF/some CMC along with gradually increasing use of the ECENS and GEFS means through next weekend. ...Sensible Weather... The Great Lakes storm system is expected to produce widespread light to moderate snow across Michigan and Wisconsin through early Thursday, with some lake enhancement to the snow likely as the low pulls away. Winds may be strong enough in some places to produce blizzard conditions. For the system near the East Coast, there has been a slightly southeastward trend in the axis of QPF, and snow is likely for inland portions of the Mid-Atlantic and Northeast and gusty winds near the coast. Heavy coastal rain and heavy mountain snow will continue to make weather headlines across portions of the Pacific Northwest, and also across the northern Rockies. Temperatures are expected to be frigid across the central/northern Plains to the Upper Midwest through the end of the week with a large surface high of arctic origin governing the weather pattern for this region. Highs in the double digits below zero are once again likely for portions of eastern Montana and into North Dakota, and highs in the teens settling as far south as southern Kansas on Thursday. Some abatement in the severe cold may come to pass across this region ahead of the next arctic surge next Sunday. Elsewhere, seasonably cold conditions are expected west of the Continental Divide with readings generally within 10 degrees of climatological averages, and cold next weekend along the East Coast with highs about 10 degrees below normal. 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