Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Fri Nov 04 2022 Valid 12Z Mon Nov 07 2022 - 12Z Fri Nov 11 2022 ...Chilly pattern over the West with significant rain/mountain snow over some areas... ...Overview... The medium range period begins Monday with an upper low over the Pacific Northwest which should amplify further and dive southward through about Wednesday before it shifts inland towards the northern Rockies/High Plains in response to another possible closed low off the Northwest coast late next week. This brings a period of widespread moderate to heavy rain/snow to much of the Western and Southwestern U.S. as well as an overall chilly temperature pattern. Meanwhile, upper level ridging should build over the East while to the south, an area of low pressure near the Bahamas next week looks to merge with energy over the eastern Gulf possibly spreading modest rainfall into some areas near the East Coast. ...Guidance and Predictability Assessment... The latest guidance shows overall good agreement through about day 5 with an amplifying trough over the West, amplifying ridging over the East/South, and some sort of subtropical feature near Florida/the Bahamas. There remain some lingering differences in the details of the Western trough and the Southeast U.S. low, but a blend of the deterministic solutions seemed to provide a good starting point while maintaining good continuity with the previous WPC forecast. After day 5/Wednesday, the GFS and ECMWF begin to shift the upper low inland over the northern Rockies/High Plains in response to another amplified trough dropping into the northeast Pacific/south of the Aleutians. The 12z/Nov 3 CMC on the other hand, was much more blocked with stronger ridging off the Pacific Northwest into Western Canada resulting in a slower/deeper troughing over the West with little to no movement eastward. A look at the ensembles also did show more support for the GFS/ECMWF solution rather than the deeper/blockier 12z CMC. As such, the WPC forecast trended towards a blend of the ensemble means with the deterministic GFS and ECMWF. A note though that the latest 00z CMC run (available after forecast issuance time) did trend east and more in line with the GFS and ECMWF. Near Florida, uncertainty increases greatly regarding interaction of an upper low in the eastern Gulf and some sort of likely subtropical low pressure area near the Bahamas. The models suggest these features should phase together around mid next week, but the ECMWF shows this feature more influenced by the approaching trough into the north-central U.S. pulling the system up the East Coast. The GFS and CMC however, keep the feature seperate and lingering over the eastern Gulf or Florida. The WPC forecast took a more conservative approach compared to the ECMWF (which would bring heavy rainfall much farther north into the Mid-Atlantic region) with a blend more towards the ensemble means and the GFS. ...Weather/Hazard Highlights... The West will see a broad area of rain and higher elevation snow during the period as the upper trough amplifies down the coast and eventually moves inland. Beginning Monday (as this event should begin this weekend during the now short range period), the highest precipitation totals should extend from the coastal ranges and Sierra Nevada in California through the Great Basin and north-central/central Rockies. Areas across the Pacific Northwest should dry out by early to 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, with more widespread rain (or snow depending on system strength) across parts of the northern Plains/Upper Midwest late week as the main trough/low moves inland. A weakening and stalling/retreating front may produce some light rainfall over parts of the East into the southern Plains early in the period as 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. Much below normal temperatures are expected to expand across the West through much of next week associated with the deepening upper trough. The coldest air will likely extend from western Canada into Montana with recent forecasts consistently showing highs in that up to 20-40F below normal Monday-Thursday, equating to daytime highs in some places in the teens and single digits (and below zero overnight lows). 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 on Monday when widespread 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. Santorelli 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