Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 643 PM EDT Wed Jul 05 2023 Valid 12Z Sun Jul 09 2023 - 12Z Thu Jul 13 2023 â€Weekend heavy rain threat and unsettled weather from the Lower Yukon to the Seward Peninsula into the western Interior and Northwest Alaska†...Overview and Weather/Hazards highlights... Organizing and complex low pressure systems with a main deepening over the Bering Sea into this weekend under influence of a closed upper low. An associated and winding frontal system will lift slowly northward over the eastern Bering and western Alaskan mainland from the weekend into early-mid next week, with eastward motion blocked by upper ridging rebuilding into eastern Alaska. This is expected to favor a weekend heavy rain/runoff threat from the Lower Yukon/vicinity and Seward Peninsula inland into the western Interior and Northwest Alaska as activity spreads up through the region with gradual system demise. Additional upper trough energies and impulses are less well depicted or as well organized for the most part unilaterially in guidance, but should be monitorred for any growing guidance signals for later through next week. Increased uncertainty still surrounds additional but less well defined in guidance possible systems set to subsequently work towards the Aleutians and Bering Sea and with associated surface system and energy with modest to locally moderate rainfall chances focus also then breaking underneath across the southern Interior and Alaskan southern tier areas and the Gulf of Alaska next week. This general pattern should keep much of Alaska cooler, with daytime highs 10-20 degrees below normal for this time of the year for at least the first half of this forecast period. The exception to this will be parts of the eastern Interior and Southeast Alaska where conditions should stay above normal and warm into at least early next week. ...Guidance Evaluation/Preferences and Predictabilty Assessment... Overall, prefer a blend of the reasonably clustered 12 UTC GFS/ECMWF/UKMET/Canadian Sunday into Monday for best product continuity and predictable detail. Manual adjustments were also applied to the main surface low pressure systems off western Alaska and the North Slope for this period to ensure sufficient depth given quite favorable upper support. WPC wind speed grids were bounced up from composite values given the smoothing effect from blending and PoP grids were increased on windward slopes and decreased leeward of terrain. Later, the models continue to show poor forecast spread and run to run continuity by Days 6-8, lending a transition mostly to the still compatible ECMWF/GEFS ensemble means as uncertainty grows. Schichtel Hazards: - Heavy rain for western mainland Alaska, Sat-Sun, Jul 8-Jul 9. 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