Extended Forecast Discussion NWS Weather Prediction Center College Park MD 205 AM EST Sun Jan 09 2022 Valid 12Z Wed Jan 12 2022 - 12Z Sun Jan 16 2022 ...Overview... The medium range period will begin on Wednesday with general ridging over the western U.S. atop a closed southern stream low near Baja California, while broad troughing ejects disturbances eastward over the north-central and eastern U.S. during the period. The southern stream low/trough should track eastward likely by late Thursday/Friday and spread increasing precipitation chances from the Four Corners states into the south-central U.S., which by the weekend could spread into the East ahead of an upper trough that may consolidate in the central CONUS. ...Guidance/Predictability Assessment... Model agreement remains reasonably good for the early part of the period Wednesday, but this consensus quickly devolves by Thursday-Friday as a few features of concern show low predictability. First, there are some differences among models with the position of the initial Pacific upper low Wednesday, but there is at least a consensus with the 12Z GFS/ECWMF/CMC in good agreement, though especially the 12Z UKMET and to some extent the 18Z GFS were centered farther southwest. The 12Z UKMET shows the feature basically eroding in place on Thursday rather than tracking eastward inland, which is not favored at this time, as other guidance (except the currently incoming 00Z ECMWF) shows the energy moving across the Four Corners and Southern Plains, though timing varies a bit. Upstream, more disagreement arises with the handling of the next Pacific trough/upper low approaching the West Coast Thursday-Friday. Most GFS runs have indicated a closed low with this feature and a slower track towards the West Coast, with recent runs showing a northeastward turn. Meanwhile guidance such as the 12Z/00Z CMC and 12Z ECMWF have an open shortwave Thursday that spills energy southeastward into the West by Friday, which may be more reasonable, but ensemble members exhibiting a huge variety in how this energy interacts and evolves with the first feature and the overall ridging, so confidence is low. Meanwhile in the East, shortwaves moving through the broad trough also display some variety among models in terms of their track and strength. One main outlier was the 18Z GFS by around Friday, which consolidated energy to create a closed mid-upper low in the western Atlantic and thus brought a deep surface low/nor'easter close to the East Coast. This track close to land is not favored and not supported by incoming 00Z model guidance either. Then a strong bout of additional energy could make its way into the Midwest on Saturday and expand troughing farther south as well, but with some variability in the trough axis and thus the associated cold frontal track and areas of possible precipitation chances for the weekend. The WPC medium range forecast blend was thus based on a blend of the 12/18Z GFS, 12Z ECMWF, and 12Z CMC deterministic guidance early on, phasing out the 18Z GFS by day 5 and lessening the proportion of deterministic models in favor of the GEFS and EC ensemble means that demonstrated okay agreement, albeit with weaker features as usual. By days 6/7 used 60% means to lessen individual model differences. ...Weather Highlights... Moderate to heavy precipitation could continue on Wednesday in the favored higher elevations of the Olympics and northern Cascades, though the heaviest precipitation is forecast over Vancouver Island as a weak atmospheric river takes aim at the region. Meanwhile, the southern stream Pacific upper low influencing the Southwest will spread precipitation to the Four Corners states and then into the Southern Plains and Lower Mississippi Valley by Thursday and Friday as it tracks inland and a low pressure/frontal system develops. Shortwaves moving through the northern stream could spread light lake effect/enhanced snow to the Great Lakes around midweek, but chances for wintry weather could ramp up by the latter part of the week for the Midwest/Great Lakes underneath the stronger shortwave energy dropping through the region. As the split flow appears to phase by next weekend, precipitation should spread to the Eastern Seaboard, with rain in the South and the possibility for snow in the Northeast, but with uncertainty in the details at this time. After a chilly day in the Eastern Seaboard on Wednesday, especially in the Northeast where lows will be 10-20F below average, temperatures should moderate closer to normal or a bit above there by the latter part of the week. The central U.S. will see considerably warmer than normal conditions, with a widespread area in the Plains/Mississippi Valley seeing highs 10-20F above average, even warmer in localized areas. Meanwhile, lows will be 15-25F above normal in the Northern Plains. Then by next weekend, as cooler high pressure systems build in behind cold fronts, highs should be right around average for this time of year in most places, with pockets that are a few degrees cooler than normal for highs, while lows should be a few degrees milder than normal in the East. Tate 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