Extended Forecast Discussion NWS Weather Prediction Center College Park MD 157 AM EST Fri Dec 31 2021 Valid 12Z Mon Jan 3 2022 - 12Z Fri Jan 7 2022 ...Coastal heavy rain and mountain focusing heavy snow threat from northern California to Washington... ...Another arctic blast for the north-central U.S. Tuesday-Thursday with snow likely for the Great Lakes and interior Northeast... ...Weather Pattern Overview... A cold Canadian surface high will settle southward across much of the central/eastern U.S. 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 by Tuesday in response to an amplifying upper trough, and another surge of arctic air behind it. Another low pressure system is on the horizon to close out the week across the East Coast, and a disturbance also takes aim at the Pacific Northwest around this same time. ...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. Timing differences are more apparent by Wednesday across the Midwest and Great Lakes region, with the GFS slower and a bit more amplified with the trough, and the CMC/UKMET slightly stronger with the southern stream shortwave crossing Texas, although these differences are well within the ensemble spread. By the end of the week, the GFS is not as amplified with the system near the East Coast compared to the CMC/ECMWF, although their overall placement is similar with the surface low. There is still very good agreement on another cold surface high settling southward across the Plains by Friday. Taking these factors into account, the WPC forecast was primarily based on a multi-deterministic model blend through early Wednesday, and then ECMWF/GFS/some CMC with gradually increasing use of the GEFS/ECENS for Thursday and Friday. ...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. 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, 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 and snow for the Appalachians may be something worth monitoring. In the temperature department, there will be a return to seasonably cold conditions across much of the Deep South and the East Coast 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. This will equate to subzero high temperatures once again across portions of northern Montana, North Dakota, and northern Minnesota. Wind chills will also reach hazardous levels for these same 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