Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 AM EST Thu Jan 07 2021 Valid 12Z Sun Jan 10 2021 - 12Z Thu Jan 14 2021 ...Overview... Trend in the upper pattern next week will favor western ridging and eastern troughing, but with an uncertain evolution of the embedded smaller-scale features. Split flow out of the Pacific will take a southern system across the Gulf and off the Southeast coast, then perhaps just offshore the Mid-Atlantic and Northeast by the middle of the week. The Pacific Northwest will continue their recent active pattern with several systems tied to the Gulf of Alaska that maintains WSW flow into coastal Washington and Oregon. Cooler than normal temperatures are forecast for the southern tier with milder than normal temperatures for the northern tier. ...Guidance/Predictability Assessment... Consensus blend approach served well for only the start of the period Sun-Mon with the developing system in the Gulf and frontal approach in the Pacific Northwest. Thereafter, GFS/ECMWF were closer in agreement with their ensembles and to each other in the West (until next Thu) as heights rise, but diverged markedly in the Southeast in timing/track of the southern system. Overall trend has been unsteadily slower but that still depends on difficult-to-predict smaller-scale shortwaves out of the northern stream, leaving a broad consensus or middle ground an attractive starting point. However, with a preference to nudge a bit slower only the 12Z ECMWF ensemble mean was near this middle ground as the GFS runs remained quickest and ECMWF slowest. Confidence remained low with this system as it would not take much to trend quicker again with a more sheared system that ejected in pieces. ...Weather/Threats Highlights... The Pacific Northwest will continue to see rounds of precipitation with few breaks during the period. Low confidence in details of shortwaves carried by fast flow aloft will temper confidence for precise intensity and southward extent at any particular time. Still the overall guidance signal is for heaviest rain/high elevation snow to be during the first part of next week (Mon-Tue) and especially over Washington. The system emerging into the western Gulf Sunday may access enough Gulf moisture to produce some locally enhanced rainfall along and just offshore from the Texas coast. Farther east, light to moderate rainfall is possible across the Deep South with enhancement near the area of low pressure should it maintain itself or deepen. Some snow will be possible over parts of the southern Plains/lower Mississippi Valley well inland. Confidence remains low for precipitation coverage and type over the East during the early/middle part of next week. Amounts could trend lower or slightly higher depending on future shifts in the track/speed/intensity. Expect locations from Montana into Minnesota to be in the core of warmest temperature anomalies through the period, with some coverage of plus 10F or greater anomalies each day. Morning lows should generally be farther above normal than the daytime highs with plus 20F or greater anomalies for lows most likely next Wed-Thu. Strengthening upper ridge should lead to more widespread plus 5-10F or so anomalies over the West Coast states into Nevada heading into midweek. Within a cool pattern for the southern tier, the best potential for highs more than 10F below normal will extend between the southern Plains and Lower Mississippi Valley from Sunday into the start of next week. Readings across the South should moderate gradually by midweek. Fracasso/Rausch 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