Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 PM 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 as a trough extends southward from a deep upper low over east-central Canada and ridging prevails 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 near the California coast through the early part of the workweek. Another Pacific shortwave should approach the West Coast around midweek with guidance showing varying ideas for what form it will take thereafter and how it may interact with the leading upper low. Meanwhile in the East, the pattern may deamplify somewhat by mid-late week but one or more shortwaves of uncertain strength and timing will likely track through the lingering broad mean trough. ...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. However the full array of guidance has not improved confidence with ongoing uncertainties in the rest of the forecast, but there are some common themes that provide decent continuity in principle. There is still a majority cluster that has a compact closed low tracking along the central-southern California coast into far northern Baja California Monday-Wednesday with subsequent ejection in response to upstream flow. The new 12Z CMC has deviated from consensus by pulling its closed low from a more southern part of the overall shortwave. Then models/ensembles continue to show their divergence for details of the next Pacific shortwave. Multiple GFS runs have been closing a low over the eastern Pacific, and now the 12Z CMC does the same farther south, while the 00Z ECMWF/CMC agreed more with the ensemble means which have been maintaining an open shortwave at least until the feature crosses the West Coast. Interestingly by late next week the 06Z/12Z GFS runs are not far from the majority solution for the large scale pattern after subtracting their eastern Pacific upper low. The 12Z ECMWF provides yet another option, trending somewhat slower/more separated and bringing the best concentration of energy into the Northwest instead of digging into the Great Basin/Four Corners. Preference based on 00Z/06Z guidance was to follow the model consensus for the leading Pacific feature and then weight the forecast more to the 00Z ECMWF/CMC and 06Z GEFS/00Z ECMWF means when the next shortwave comes into the picture. Meanwhile in the broad cyclonic flow farther east, the best signal exists for a shortwave to cross the eastern half of the country around Wednesday-Thursday. As can be the model's occasional bias with upper troughs, the latest CMC runs are quite amplified (even pulling off a closed low east of Florida by Friday in the new 12Z run). Even if not quite an outlier, these CMC runs are extreme compared to most of the full ensemble envelope. The late-period transition to half means/half models (versus all models early) kept somewhat more 00Z ECMWF input relative to the 06Z GFS/00Z CMC given the desire to downplay GFS specifics near the West Coast and the CMC in the East. ...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. Locally moderate to heavy activity may be possible over the Olympics and vicinity around midweek when the area may be on the southeast fringe of an atmospheric river event aimed at Vancouver Island. The upper low initially dropping southward near the California coast may spread moisture into the Southwest by Tuesday-Wednesday. This precipitation should be fairly light but heavier rainfall may develop over the Southern Plains and Lower Mississippi Valley by mid-late week as the upper low tracks/shears northeastward and the surface pattern becomes more favorable for drawing moisture northward from the Gulf of Mexico. It will take additional time to refine the details of rainfall coverage and magnitude though. 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 the central U.S. will see a pronounced warming trend next week with expanding coverage of max/min temperatures 10-20F above normal Tuesday onward. Some locations in the northern two-thirds of the Plains may see even warmer readings mid-late week. Across the West expect to see daytime highs within 10F on either side of normal through the period, while above normal lows should become more prevalent with time. Best potential for one or more days with plus 10F or greater anomalies for lows would be over the Southwest and Pacific Northwest as separate features bring clouds/moisture into those regions. Rausch/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