Extended Forecast Discussion NWS Weather Prediction Center College Park MD 229 PM EDT Sat Nov 06 2021 Valid 12Z Tue Nov 09 2021 - 12Z Sat Nov 13 2021 ...Pattern Overview... A trio of positive height anomaly centers over far northern Canada and just off the Southwest and Southeast U.S. will favor increased troughing over the middle of the Lower 48 toward the end of next week. This favors a deepening cyclone over the central states that will lift north-northeastward through the Great Lakes into southeastern Canada. Milder air over much of the Lower 48 midweek will trend cooler with time as the front progresses eastward. ...Guidance/Predictability Assessment... The latest suite of guidance continues to illustrate a reasonably similar larger scale pattern evolution, but with continued uncertainty in timing, track, and strength of the embedded systems. Right off the bat, the 00Z/06Z GFS remained different (much slower) with the exiting Southeastern U.S. trough, showing more defined northern/southern stream separation and a stronger/more south surface low off the FL/GA coast. Models and ensembles showed much larger and pertinent spread as upper troughing digs east of the Rockies. This resulted in rather large differences between the ensemble systems' trough axes and resultant temperature trends/averages especially into the Front Range of the Rockies and western Plains. Favored the more steady ECMWF ensemble guidance which was generally milder than the GEFS guidance but with tempered confidence due to uncertainty in the mid-latitude flow progression from the North Pacific into western North America. Multi-day trend favored a bit quicker progression of the upper trough overall. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of the 00Z ECMWF/Canadian/UKMET and 00Z ECMWF ensemble mean guidance to start, though the GFS/GEFS were reasonable over the western portion of the CONUS. Once the Atlantic system (slow GFS) exited well away from the coast, the GFS was brought back into the mix at the expense of the UKMET and Canadian, which added detail to the ECMWF ensemble mean (and some GEFS mean influence to adjust timing). Favored a milder pattern than the 13Z NBM over the Plains (quicker to raise heights) and wetter overall as the increasingly meridional flow should tap at least a modest amount of Gulf moisture along and ahead of the front. ...Weather/Hazards Highlights... A series of Pacific systems will work inland across the West, with main upper troughing set to work through the region by midweek. This will favor terrain-enhanced rainfall from the Pacific Northwest to northern California and a heavy snow threat from the Cascades and northern Sierra inland across favored terrain for the north-central Great Basin/Rockies early in the period, with rising snow levels toward the end of next week as heights recover. Subsequent amplified upper troughing carving out over the central U.S. is slated to be sandwiched between upper ridges over the West Coast and East Coast amid the pattern transition. Cyclogenesis and frontogenesis will act to favor an emerging lead organized rainfall/convective pattern over the east-central U.S. Thursday as theta-e advection increases. Surface wave development could act to enhance rainfall along the front from the southern Appalachians northward. Backside cold air flow by next Friday also suggests potential for some snow over the Dakotas/Upper Midwest as moisture feeds back around the developing/exiting main low. Temperatures will be near to above normal early in the week, with possible record highs ahead of the front, trending cooler by week's end especially into the Southeast. Please see WPC links below for all the details in graphical format. Fracasso/Schichtel 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