Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 603 PM EDT Sun Jul 16 2023 Valid 12Z Thu Jul 20 2023 - 12Z Mon Jul 24 2023 ...Wet pattern from Western Alaska to the Alaskan Peninsula and from Southeast Alaska to the Southeast Mainland... ...Guidance Evaluation/Preferences and Predictability Assessment... A composite of decently clustered 12 UTC GFS/ECMWF/UKMET/CMC guidance overall seems reasonable Thursday into Saturday. Prefer to add to the mix the compatible GEFS/NAEFS/ECMWF ensemble means into next week amid growing system uncertainties. A clear trend toward deeper upper trough development over western Alaska later this week seems reasonable to the lee of an amplified upper ridge now in most guidance. There is also a growing guidance signal to strongly build upper ridging back across the Interior into next week to significantly transition the pattern to one with more separated Arctic and Pacific stream flows. Plan to again apply manual adjustments as required to offset the blending process to ensure sufficient low pressure system depth and wind speeds under favorable upper support in guidance. ...Weather/Hazards Highlights... An amplified and slow moving closed upper trough and deepening surface based low over the Gulf of Alaska to the east of an anomalously amplified upper ridge will present a protracted maritime threat over the next week. Easterly waves rotating overtop from Southeast Alaska to eastern Southcentral/Alaska Range and southeast Interior will support uncertainly timed daily bouts of enhanced rains across the broad region, but especially into locally favored terrain of the Southeast by next weekend with closer proximity of the closed low offshore over the Gulf of Alaska that is trending favorably in most guidance. Meanwhile, expect increasing and more widespread rains and unsettled weather will work through especially western and southwestern Alaska/Alaska Peninsula mid-later week with approach and increasingly robust digging of a Bering Sea system set to round through the northern periphery of the aforementioned upper ridge. Additional Pacific energies are also slated to work eastward across the Aleutians in this pattern by next weekend in emerging flow across the northern Pacific. 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