Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Sat Nov 05 2022 Valid 12Z Tue Nov 08 2022 - 12Z Sat Nov 12 2022 ...Possibly significant rain/mountain snows across parts of California and the Great Basin into Tuesday, with an overall chilly pattern over the West the rest of the week... ...Overview... Upper trough amplification will be underway along the West Coast as the period begins Tuesday eventually shifting inland towards the northern Rockies/High Plains mid to later next week. Heavy rain/mountain snows are likely across parts of California and the Great Basin through Tuesday, as much below normal temperatures spread across the West. Meanwhile, upper level ridging will prevail across the Eastern U.S. through about Thursday before some sort of hybrid/subtropical feature over the Bahamas/Florida may get wrapped up into the approaching trough from the West. This could spread modest rainfall into some areas near the East Coast later next week. ...Guidance and Predictability Assessment... Latest guidance seemed agreeable enough on the upper pattern through day 4 for a purely deterministic model blend. After this time, models really begin to diverge on the evolution of the Western U.S. trough into the central U.S. and the East later next week. The guidance does suggest the pattern should remain rather amplified through the medium range, but poor run to run continuity in all of the guidance lends to a very low confidence forecast. The ECMWF is the most amplified with the late week pattern showing closed lows over both the Midwest and the Northwest by next Saturday/day 7. The GFS is a little weaker and faster, and maybe more in line with the ensemble means, at least for now. The CMC looks reasonable in the East but gets totally out of phase out West showing strong ridging over the West Coast while the better consensus shows at least some kind of shortwave into the region. Given the spread, the WPC forecast trended fairly quickly towards the ensemble means for the latter half of the period. The evolution of a disturbance in the western Atlantic/near the Bahamas is uncertain as well with a number of deterministic and ensemble guidance carrying a closed upper low across the Florida peninsula before likely getting wrapped into the Eastern U.S. trough. This feature will need to be monitored in the coming days, and the National Hurricane Center is watching it for any potential tropical characteristics. ...Weather/Hazard Highlights... Modest rainfall and possibly significant mountain snows will be ongoing across parts of the West as the period begins. The heaviest snow totals on Tuesday are likely to be in the Sierra Nevada in California through the Great Basin and central Rockies where total snow accumulations in some places could measure several feet. Locally heavy rains are possible in lower elevations and along favorable upslope terrain, particularly across parts of southern/coastal California. Anomalous moisture ahead of this trough as it moves into the central U.S. will likely spread moderate to locally heavy rainfall into parts of the northern tier with some snow also possible on the backside of the low in the northern Plains. Despite plenty of uncertainty in the details still, the disturbance moving towards Florida mid next week continues to show an increasing threat for coastal and maritime impacts, including heavy rain, coastal flooding, high waves, and rip currents. Moisture from this system should move up the East Coast later in the week, although amounts and coverage remain highly uncertain still. 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 area up to 20-40F below normal Tuesday-Thursday, equating to daytime highs in some places in the teens and single digits (and below zero overnight lows). Many locations over the West could see daily records for cold highs through Wednesday. In contrast, well above normal temperatures will progress from the Central Plains to the East Coast with widespread daily records for warm lows possible. Tuesday-Wednesday should be the warmest days for the Plains to the Upper Midwest with readings 10-20F or so above normal. A strong cold front through this region by Thursday will usher in a much colder airmass, with high temperatures by Friday and Saturday in the Plains as much as 10 to 20 degrees below 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