Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Thu Nov 03 2022 Valid 12Z Sun Nov 06 2022 - 12Z Thu Nov 10 2022 ...Chilly pattern over the West with significant rain/mountain snow over some areas... ...Overview... Guidance trends over the past day have yielded improved agreement in principle for the shape of strong upper ridging forecast to build into Alaska and northwestern Canada. As a result the latest models/means are now better clustered for the downstream evolution from the eastern Pacific through the lower 48. Current consensus shows a strongly amplifying trough near the West Coast Sunday-Tuesday, anchored by an upper low drifting southward just west of Vancouver Island and Pacific Northwest coast. Then the trough should progress inland during Wednesday-Thursday. The early week deepening of the trough will serve to rebuild an upper ridge over the East. Meanwhile most solutions show an upper low initially near the eastern Bahamas tracking into Florida or southeastern coast, underneath the ridge that builds farther north. The western trough will bring multiple days of well below normal temperatures and a broad area of rain/mountain snow, with significant totals over some areas. Ejecting energy/moisture could spread some precipitation farther east across the northern tier. On the other hand most of the eastern half of the country will see unseasonably warm temperatures and the Bahamas system may eventually spread rainfall into some areas near the East Coast. ...Guidance and Predictability Assessment... There is still a window for more changes to occur, but with other guidance over the past 24-36 hours gravitating to the prior GFS/GEFS idea of an open ridge building into Alaska/northwestern Canada leading to strong West Coast trough amplification, confidence is finally increasing that this is the most likely scenario to occur. This evolution over the West has led to stronger trends for ridging that builds over the East, and in turn potentially a farther south track of the Bahamas system compared to some runs from previous days. With respect to specifics, there is now decent clustering with most aspects of the forecast into early day 5 Tuesday. This favored a 12Z/18Z operational model composite for the preparation of the latest forecast. The new 00Z GFS brings the core of its upper system a little south of other solutions by Tuesday but is still within the realm of possibility. Farther east, an initial Midwest cold front trailing from a southern Canada system makes greater southward progress over the East than prior consensus by Tuesday and the stronger trend for eastern upper ridging slows the retrogression of the Bahamas system. By days 6-7 Wednesday-Thursday, some typical spread develops for how leading energy may eject from the western trough--leading to differences for northern tier U.S./southern Canada low pressure--and for details/timing of the western trough itself. The ultimate path of the Bahamas system will depend on how quickly the center of the eastern upper ridge shifts into the Atlantic. The GFS has been more persistent with the ridge, keeping the system farther south relative to the past couple ECMWF runs through 12Z. Both the 00Z ECMWF and CMC have flipped from their 12Z runs, the new ECMWF switching to the GFS idea and the CMC switching from the GFS type solution to looking more like the 12Z ECMWF. Needless to say, confidence is still below average for this aspect of the forecast. A general model/mean blend provided a good intermediate depiction for the features of interest during days 6-7. ...Weather/Hazard Highlights... The West will see a broad area of rain and higher elevation snow during the period as the upper trough amplifies near the coast and eventually moves inland. Strong leading dynamics will initially provide the best rain/mountain snow focus over western Oregon and northern California on Sunday. Broad southerly flow east of the offshore upper low could also enhance precipitation over parts of northern-northwestern Washington. From Monday onward the highest precipitation totals should push southeastward, extending from the coastal ranges and Sierra Nevada in California through the Great Basin and north-central/central Rockies. Westernmost areas should begin to see a drier trend around midweek. Moisture/energy ejecting from the western trough may spread one or more areas of precipitation across the northern tier during the first half of next week. Best snow potential should be over Montana with the cold air in place over the area. A weakening and stalling/retreating front may produce some light rainfall over parts of the East into the southern Plains early in the period. Moisture associated with the Bahamas system tracking toward Florida/southeastern coast may spread into parts of the East Tuesday onward. Details of coverage and totals are still fairly uncertain at this time, but some areas of locally moderate to heavy rainfall may be possible. The West will see a brief recovery to only moderately below normal temperatures extend into Sunday. Then the amplifying upper trough near the West Coast should spread an increasing area of highs 10-20F below normal across the region during Monday-Thursday. The coldest air will likely extend from western Canada into Montana with recent forecasts consistently showing highs in that state up to 20-35F below normal Monday-Thursday. Some locations over the West may see daily records for cold highs Monday-Wednesday. In contrast, well above normal temperatures will prevail over much of the East and at times over the Plains. The East will see temperatures 10-25F above normal especially during Sunday-Monday when daily records for highs and/or warm lows are possible. Highs will moderate near the East Coast thereafter with increasing clouds/moisture but lows will remain unseasonably warm. Tuesday-Wednesday should be the warmest days for the central-southern Plains with readings 10-20F or so above normal. 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml