Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Tue May 16 2023 Valid 12Z Sat May 20 2023 - 12Z Wed May 24 2023 ...Spring warming to advance interior snowmelt runoff and river ice breakup and flooding threats this week... ...Guidance Evaluation/Predictability Assessment... The medium-range period will likely feature a zonally-oriented upper ridge across the northern and eastern Alaska while various vorticity centers will attempt to merge and/or rotate about a mean center near/over the Aleutians. This pattern will continue to contribute to below normal predictability for areas south of the relatively stable and more predictable upper ridge. The first system of concern should be pushing north into the eastern Aleutians and the Alaska Peninsula this weekend as it rapidly weakens. Farther upstream, model consensus today indicates a stronger and more consolidated cyclone to approach the central Aleutians from the south by next Monday. The QPF footprint for early next week generally favors the faster ECMWF/CMC solutions, leaving the slower and farther offshore solutions from the GFS to be the outlier. The 18Z GFS appears to correct itself with a significant jump of the triple-point low to the northeast next Monday. Predictability of individual waves drops off thereafter. Nevertheless, there appears to be a consensus for gradual weakening of the system by midweek next week as it moves slowly toward the east. Therefore, the WPC forecast package for Alaska was based on a composite model blend of 40% from the 12Z ECMWF/00Z/12Z EC mean, 40% from the 12Z GFS/GEFS (with minimal use of the GFS by Day 6.5), and 20% from the 12Z CMC/CMC mean. Manual edits were applied to the isobars to ensure sufficient surface low pressure center depths and wind speeds as supported aloft, but otherwise they were muted by the blending process and forecast spread. ...Overview and Weather/Hazard Highlights... Persistent upper ridge across northern and eastern Alaska will maintain warmer than normal temperatures across much of the interior sections through the medium-range period. This will likely continue the snowmelt runoff and river ice breakup that are expected to lead to flooding threats for southwestern Alaska at least through Friday. Please refer to ongoing advisories and watch/warnings from your local weather offices for impacts, details and needed actions. An occluded cyclone is forecast to move into the eastern Aleutians and the Alaska Peninsula this weekend as it rapidly weakens and dissipates. Another occluded cyclone should bring the next round of precipitation again into eastern Aleutians and the Alaska Peninsula early next week with a gradual tapering off trend into midweek. Overall, no big storms are anticipated to impact Alaska through the medium-range forecast period. Kong Hazards: - Flooding possible across portions of mainland Alaska, Fri, May 19. 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