Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Tue Jul 18 2023 Valid 12Z Sat Jul 22 2023 - 12Z Wed Jul 26 2023 ...Rain lingers across portions of southern to southeastern Alaska with very warm temperatures over the interior and North Slope... ...Pattern overview with Guidance Evaluation/Preferences and Predictability Assessment... A Rex block pattern is forecast to set up over the Alaskan domain during the medium-range period as three upper lows--one centered southeast of the Gulf of Alaska, another over the Bering Sea, and still another near the North Pole--anchor an upper ridge across mainland Alaska into northwestern Canada. Model guidance remains in decent agreement with this slow-to-evolve pattern over the Alaskan domain, including the merger of two upper troughs in the short-range period into the aforementioned upper low over the Bering Sea when the medium-range period begins late this week. Farther south across the northern Pacific though, there is noticeable disagreement on the timing of the eastward-traveling shortwaves closer to the main jet stream. Elsewhere, differences in the placement of the upper low over the Arctic Ocean appear significant. Toward the end of the medium-range period, the 12Z ECMWF favors a retrogression of the Bering Sea low in disagreement with the 00Z EC mean as well as the rest of the model guidance. It also favors a stronger influence of the upper ridge northward into the Arctic Ocean by midweek next week. Therefore, the WPC Alaskan forecast package was based on a composite blend of the deterministic and ensemble guidance of about 40% from the 12Z ECMWF/00Z EC mean, 40% from the 12Z GFS/GEFS mean, and 20% from the 12Z CMC/CMC mean, with increased proportion from the ensemble means toward the end of the forecast period. ...Weather/Hazards Highlights... As the Rex block sets up over the Alaskan domain, persistent southeasterly flow around the upper low centered southeast of the Gulf of Alaska is forecast to transport antecedent moisture from southeastern Alaska over the weekend into southern Alaska early next week, and eventually into western Alaska by midweek next week. Rain amounts should generally be light to moderate but may be enhanced by local terrain and daytime heating over portions of southeastern/interior southern Alaska early next week. In the meantime, subsidence associated with the upper ridge farther north will provide very warm afternoons from the North Slope, where highs could reach 80 degrees, to the interior section of eastern Alaska, where highs could approach 90 degrees. Across eastern Aleutians, the moist south to southeasterly flow ahead of the Bering Sea low is forecast to keep a good chance of rain for the region especially during the weekend. Kong 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 Hazards: No significant hazards are expected over Alaska during this forecast period. 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