Extended Forecast Discussion NWS Weather Prediction Center College Park MD 418 PM 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... A general model blend consisting of this morning's 00z EC/CMC/UKMET and 06z GFS was used through day 5. The UKMET and GFS were phased out on days 6 and 7 while ensemble mean weighting was increased. The main areas of uncertainty revolved around the timing of the upper low moving into the CONUS via the West Coast next week. The deterministics have good agreement with it's evolution until day 5 when even the ensembles begin to struggle a bit with it's orientation across the central part of the country. The 06z GFS had notable run to run inconsistency with respect to the mean trough's propagation from the Rockies into the Plains mid-late next week. This was reflected in the qpf where the 00z and 06z completely differed with their axes of highest qpf over the Upper-Midwest/Northern Plains. The evolution of a disturbance in the western Atlantic is uncertain as well with a number of determinstic and ensemble means carrying a closed upper low across the Florida peninsula and into the Gulf of Mexico next week. We'll need to monitor this closely over the coming days. ...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. Kebede/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 Hazards: - Heavy rain across portions of California, Mon-Tue, Nov 7-Nov 8. - Heavy snow across portions of the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, California, and the Southwest, Mon-Tue, Nov 7-Nov 8. - Heavy snow across portions of the Northern Plains and the Northern Rockies, Mon, Nov 7. - Flooding possible across portions of the Great Lakes, the Southern Plains, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Southeast, the Pacific Northwest, and the Northern Great Basin. - Flooding likely across portions of the Pacific Northwest. - High winds across portions of the Southern Rockies, the Central Rockies, the Central Great Basin, the Northern Great Basin, and the Southwest, Mon-Wed, Nov 7-Nov 9. - High winds across portions of eastern Florida, the Southeast, and the Mid-Atlantic, Tue-Wed, Nov 8-Nov 9. - Much below normal temperatures across portions of the Northern Plains, the Northern Rockies, and the Northern Great Basin, Mon-Fri, Nov 7-Nov 11. 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