Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EDT Sun Sep 04 2022 Valid 12Z Thu Sep 08 2022 - 12Z Mon Sep 12 2022 ...Heavy precipitation/wind/atmospheric river threat inland from the Gulf of Alaska to south-central/southeast Alaska and the Interior Thursday/Friday... ...Bering Sea system threat slated to affect western/southwestern Alaska next weekend... ...Guidance/Predictability Assessment... Stream phasing differences in guidance lead into this medium range forecast period to complicate the expected development of an energetic Thursday/Friday storm lifting into Alaska, with the 12 UTC ECMWF/UKMET/Canadian and ECMWF ensemble solutions better clustered with WPC continuity than the GFS/GEFS. The more amplified solution of the 06/12 UTC GFS/GEFS runs, while in the minority, is still plausible considering possible downstream effects from current west Pacific Typhoon Hinnamnor. However, there is concern with recent run to run continuity issues. That said, all these solutions show a significant system but vary with local focus. The WPC medium range product suite was derived mainly from a composite blend of the 12 UTC ECMWF/UKMET/Canadian and the 19 UTC National Blend of Models for Thursday before increasingly leaning on the latest ECMWF ensemble mean Friday past next weekend, added by some added detail via the sister ECMWF deterministic run. This maintained decent WPC product continuity. This forecast plan was collaborated with Alaskan NWS weather offices in Fairbanks, Juneau and Anchorage. ...Sensible Weather and Potential Hazards... A main emphasis of the forecast past midweek will concern the evolution of upper trough energies and embedded lows digging from the Bering Sea to the south of the Aleutians along with how they may interact with North Pacific flow/surface system as amplifying upper troughing feed development. WPC surface progs lift a deepened low/frontal system well inland from the Gulf of Alaska into Thursday/Friday along with potential triple point low reformation. There is a strong forecast signal that this storm will offer a multi-day southern to southeastern Alaskan to Interior threat of enhanced rains/winds and mountain snows given ample upper support, surface organziation and as per a potential atmospheric river set to focus into southern to southeast Alaska. Upstream, energetic flow off eastern Asia early next week to include the deepened and moist extratropical low associated with current west Pacific Typhoon Hinnamnor and lead low developments are subsequently slated to work increasingly eastward into the Bering Sea, albeit with quite a bit of system evolution uncertainties given system interaction variances in guidance. System combination and nature offers potential for deep low development contingent on energy consolidation. Accordingly, expect a maritime wind/waves threat over the Bering Sea by mid-later this week along with an emerging longer time frame threat of enhanced rain/winds with possible well organized system approach toward the western mainland through next weekend. 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 Alaskan products including 500mb, surface fronts/pressures progs and sensible weather grids can also be found at: https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html