Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Fri Jan 07 2022 Valid 12Z Mon Jan 10 2022 - 12Z Fri Jan 14 2022 ...Overview... The medium range period will begin on Monday with an amplified upper flow pattern with a trough stemming southward from a deep upper low over east-central Canada and ridging across the western U.S. and Canada. A split flow pattern is likely to develop across the eastern Pacific and West, as a southern stream low drops southward just west of California through the early part of the workweek. Meanwhile in the East, the pattern may deamplify somewhat but rounds of shortwave energy will likely track through the broader trough axis. ...Guidance/Predictability Assessment... Reasonably good predictability exists early in the period as model guidance has remained consistent and agreeable with the deep upper trough across the East and ridging across the West. Guidance from the 12Z/18Z (yesterday) cycle also agrees fairly well with the existence of energy dropping southward through the Pacific and forming a closed southern southern stream upper low, with generally similar timing to the previous forecast cycle with it migrating slowly and staying west of Baja California through early Wednesday. The incoming 00Z model guidance also shows a similar idea, though the 00Z CMC has the low staying open for longer. The upper low/trough may finally get kicked out by Thursday as additional Pacific energy approaches. However, the evolution of this energy and additional narrow ridging coming in behind remain uncertain with quite a bit of ensemble spread, though the recent GEFS and EC ensemble means do show hints of this shortwave energy now. At this point, the 12Z ECMWF and CMC and the 18Z GFS (rather than the 12Z GFS) seemed to have the best agreement with these features, but with low confidence. Additionally, northern stream impulses moving through the mean cyclonic flow in the East show some differences in strength and position especially during the second half of the week. Thus for the WPC medium range forecast, used a blend of the deterministic 12Z ECMWF/CMC and 18Z GFS for the early part of the period, then phased in some 18Z GEFS and 00Z EC ensemble mean gradually to about 40% (60% operational models) by the end of the period. This served to minimize individual forecast differences but maintain some strength of systems, and provided good continuity with the previous forecast on days 3-6. ...Weather Highlights... Drier conditions are likely over much of the contiguous U.S. for the early part of next workweek as large surface highs influence the Intermountain West to the central U.S. behind a cold front. Showers could linger over Florida on Monday as the front passes through, while generally westerly flow causes lake effect snow downwind of the Great Lakes especially on Monday, but with the possibility for additional rounds as the week progresses. The Pacific Northwest should see periods of precipitation as fronts approach the area, with higher totals over typical upslope areas of the Olympics and Cascades. Then moisture may spread ahead of the upper low in the eastern Pacific into the Southwest. Precipitation totals are expected to be light in the Southwest, but could increase into the Southern Plains and Lower Mississippi Valley by Wednesday and Thursday as the low tracks eastward and also draws moisture from the Gulf of Mexico. However, confidence in the details of rainfall amounts is somewhat low and will likely be refined in future forecast updates. The next round of arctic air will be in place across the Northern Plains and Upper Midwest on Monday, with temperatures of 10-25F below normal and maximum temperatures staying below 0F in some areas. By Tuesday this chilly air will spread into the Northeast/Mid-Atlantic in modified form, with high temperatures 10-30F below average for one of the coldest days of the season thus far. Then, te central U.S. will see a pronounced warming trend next week with expanding coverage of max/min temperatures 10-20F above normal Tuesday onward with some locally warmer readings possible on some days. Expect most of the West to see temperatures within 10F on either side of normal through the period. 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