Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1033 AM EST Sun Nov 14 2021 Valid 12Z Wed Nov 17 2021 - 12Z Sun Nov 21 2021 ...Overview and Guidance/Predictability Assessment... Models and ensembles continue to show a progressive pattern with broad cyclonic flow across most of the lower 48 while an upstream ridge builds over the eastern Pacific next weekend. Guidance remains fairly well clustered for a strong southern into eastern Canada storm system and trailing cold front sweeping through the eastern half of the country mid-late week. Specifics over the eastern Pacific Wednesday-Thursday and continuing eastward across the lower 48 appear to be clearing up. The 00z UKMET is weaker than the 06z GFS/00z ECMWF/00z Canadian which are quite agreeable -- went towards the growing consensus for the manual progs. The relative improvement in clustering for a meaningful eastern Pacific into western U.S. shortwave after midweek has brought guidance closer together for the lower 48 pattern by mid-late period. The most common theme in the guidance at the moment is for a frontal system to reach the Plains by Saturday and continue eastward into Sunday. The ridge that builds off the West Coast during the weekend may support elongation of upper troughing into the Southwest U.S., which would lead to some deceleration of the front over the southern Plains. The 00Z ECMWF has shifted noticeably farther west with the upper ridge versus continuity, which allows a stronger shortwave/closed low to move through British Columbia Saturday into next Sunday which will be watched, but is not presently preferred. To account for lingering uncertainty, a compromise of the 00z UKMET/00z GFS/00z ECMWF/00z Canadian was used early for pressures/500 hPa heights, winds, and generally for QPF before using increasing amounts of ensemble mean (ECMWF/NAEFS) solutions with time. The remainder of the grids used the 13z National Blend of Models as a baseline. ...Weather/Hazards Highlights... The vigorous surface low tracking across southern into eastern Canada mid-late week will bring a period of strong winds to northern tier areas, especially the Northern Plains into Wednesday and perhaps to some degree locations farther east thereafter. Expect mostly light to moderate rain to develop along the trailing cold front over the east-central U.S. around Wednesday and progress eastward/northeastward into Thursday. Highest totals should extend from the south-central Mississippi Valley up the Ohio Valley. Chilly flow behind the system may produce a period of lake effect precipitation, mainly over the upper and eastern portions of the Great Lakes. The southern Florida Peninsula will see increasing rainfall mid-late week as moisture interacts with a stalled front to the south. Easterly low level flow should lead to highest totals over eastern areas. Meanwhile, a Pacific system reaching the northern half of the West Coast after midweek will produce organized precipitation over central/northern parts of the West, which for Western WA could persist through next weekend. The upper level portion of this system may support a central U.S. front that could start to produce some rain next weekend. Overall expect temperatures across the lower 48 to reach fairly seasonable levels by next weekend with many locations seeing highs within a few degrees of normal. Before then, the warm sector ahead of the front crossing the eastern half of the country Wednesday-Thursday will bring a brief period of warmth to the South and East as temperatures reach up to 10-15F above normal (perhaps even warmer for morning lows on Wednesday). Colder air behind the front will spread from the Plains into the East mid-late week with readings generally 5-10F or so below normal. Parts of the High Plains could rebound to scattered plus 10F anomalies on Friday. Roth/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