Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Thu Oct 27 2022 Valid 12Z Sun Oct 30 2022 - 12Z Thu Nov 03 2022 ...Pacific Northwest heavy rains and Northwest to Great Basin/Rockies heavy mountain snow threat next week... ...Guidance and Predictability Assessment... The WPC medium range product suite was primarily derived from a composite of reasonably well clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian for Sunday along with compatible input from the 01 UTC National Blend of Models (NBM) and WPC continuity. 00 UTC model and ensemble guidance remains in agreement. Ample Pacific system energies are set to work into the Northwest/West through medium range time scales, but large flow differences again grow more than usual early next week and steadily translate downstream over the rest of the lower 48. 12/18 UTC GFS runs offer a western U.S. upper trough solution on the amplified side of guidance over time in stark contrast to a seemingly outlier flatter 12 UTC ECMWF. Ensemble means support trough amplification 3/4 of the way toward the GFS. This seems reasonable considering upper ridge amplification potential upstream over the Pacific, but cognizant of forecast spread. The most compatible 12 UTC NAEFS/ECMWF ensemble means seem to offer a good and consistent forecast basis across much of the lower 48 next week. Latest 00 UTC model guidance offers hope for improving forecast confidence next week as atrocious run to run continuity in both the UKMET and ECMWF now show a substantial trend to the favored NAEFS/ECMWF ensemble means. ...Pattern Overview and Weather/Hazard Highlights... Expect favorable dynamics and moisture to fuel periods of moderate to locally enhanced precipitation with overall focus likely to gradually spread out from the Pacific Northwest into California and farther inland across the north-central Great Basin/Rockies next week with flow amplification. This will offer heaviest rainfall potential for the coastal ranges/Olympics and Cascades of the Pacific Northwest starting this weekend along with a threat for heavy mountain snows set to also spread next week into California and across the north-central Great Basin/Rockies as depicted in the WPC Winter Weather Outlook probabilities. Southern stream system energies will lift a swath of rainfall through the length of the east-central U.S. Sunday into early next week to include a moderately heavy rainfall focus across the Upper Ohio Valley and Appalachians to the Mid-Atlantic/Northeast for Halloween as lead system and upstream upper trough energy reinforcement work into blocky lead ridging. Expect modest coastal triple point genesis may focus some Atlantic moisture to supplement lingering Gulf moisture. 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, 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