Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 725 PM EDT Wed Jun 07 2023 Valid 12Z Sun Jun 11 2023 - 12Z Thu Jun 15 2023 ...Slow moving eastern Aleutians into Bering Sea deep layer low likely to maintain a wet pattern across much of Alaska into next week... ...Overview... A persistent upper low will meander with its centroid over the eastern Aleutians/southern Bering Sea/Bristol Bay region early-mid next week. An associated surface low is forecast to track across the Alaska Peninsula around day 4/Sunday and enhance rain totals from the Peninsula into Southcentral Alaska. Some moisture streaming farther north combining with shortwaves should lead to rounds of rain across the Interior as well through next week. The mean low will likely weaken a bit with time, though the overall flow becomes more uncertain as the period progresses as high latitude flow shows some differences in model guidance. It seems probable in general that eastern parts of the state should see rising heights with time as ridging develops across the eastern Pacific. ...Guidance Evaluation/Preferences... Model guidance shows good agreement through about the day 4-5 part of the forecast period as the large scale Aleutians/Bering Sea upper low dominates the pattern. The latest 12Z guidance shows a good consensus for a vorticity max/spoke of the upper low to track north across the Alaska Peninsula Sunday, with better agreement than previous days for the associated surface low to do the same. This provides an elongated west-east upper low pattern for Sunday-Monday but a more rounded low/trough pattern by Tuesday and beyond across the Bering/western Alaska, with a general trend for the upper low to weaken with time, while farther east some minor ridging or at least rising heights will be likely by midweek. The more uncertain aspect of the forecast will be with the high latitude/Arctic flow. Models vary with the track of an upper low beginning well northwest of Alaska but having potential influence on the Alaska pattern by days 6-8. GFS runs indicate this upper low dropping southeast while the ECMWF/CMC take it east, so farther north of the GFS runs. This has the impact of the GFS runs pushing the original upper low farther south, especially the 12Z GFS that shows it south of the Aleutians by midweek. The ensemble means support something farther north, keeping the low in the Bering Sea, more like the ECMWF and CMC runs, so the GFS was not favored by the mid-late period. Meanwhile, though there are some differences in timing and position, models generally show that what is currently Tropical Storm Guchol in the western Pacific should likely transition to post-tropical and track south of the Aleutians by Thursday, with another surface low east of it in the northern Pacific (south of the state). Considering the above, the model blend for days 4-5 was based on the 12Z deterministic ECMWF/GFS/CMC/UKMET. Transitioned to a blend lessening the GFS (and of course the UKMET as its run ends) and ramping up the GEFS/ECMWF ensemble means to half by days 7-8 amid increasing spread. ...Sensible Weather and Potential Hazards... The quasi-stationary upper low atop the Bering Sea/eastern Aleutians will direct moist southerly flow into much of the state next week. The Alaska Peninsula surface low should help focus the moisture and enhance precipitation totals for the Peninsula into Kodiak Island and Southcentral Alaska around Sunday. Most of this will be rain with perhaps some snow in the highest elevations, and some localized gusty winds are possible with the low as well. By Sunday night and Monday the frontal system associated with the low should spread enhanced rainfall amounts into Southeast Alaska. Precipitation is likely to be lighter farther north, but chances will be widespread through much of the week given the moisture in place for a prolonged period of unsettled weather. Given the precipitation potential and widespread clouds in place, below normal high temperatures should be common across much of the state next week. This is especially over southern portions of Alaska, but central/northern portions are likely to cool off quickly during the workweek. Lows should be closer to normal, with a mix of below/above normal anomalies but perhaps more coverage of below average lows likely by midweek. Tate Hazards: - Heavy rain across portions of interior Alaska, Sat, Jun 10. - Heavy rain across portions of the Alaska Peninsula and coastal Southcentral, Sun, Jun 11. 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