Extended Forecast Discussion NWS Weather Prediction Center College Park MD 410 PM 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 deterministic guidance days 3-5, with more incorporation of the ensemble means days 6-7 given increased forecast spread, as described below. This maintains good continuity with the previous WPC forecast as well. Ample Pacific system energies are set to work into the Northwest/West through medium range time scales, with some continued uncertainty by mid next week. The latest GFS runs have been consistent in showing a more amplified solution, but the 00z ECMWF run today trended in that more amplified direction as well. Main differences surrounding this deep trough are now tied more to timing, with the GFS/GEFS slower than the ECMWF/ECENS and CMC. WPCs forecast today favored a more middle ground solution right now. Only other thing to note across the CONUS with the pattern is a few shortwaves moving from the Southern Plains into the Mid-Atlantic/Northeast which show typical medium range time scale differences and a general model blend seems to work well. ...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. Temperatures across the entire Western U.S. will trend much colder as the trough amplifies along the coast next week. Daytime highs in many locations could be 10 to 20 degrees below normal. 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 moderate to locally 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. Temperatures behind and to the north of this system should trend warmer across the north-central U.S. through the period as upper ridging moves through. Santorelli/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 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Oct 30-Oct 31. - Flooding occurring or imminent across portions of Florida. - Heavy precipitation across portions of the Alaska Panhandle, Sun, Oct 30. - High winds across portions of mainland Alaska, Sun-Mon, Oct 30-Oct 31. 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