Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Tue Sep 17 2024 Valid 12Z Sat Sep 21 2024 - 12Z Wed Sep 25 2024 ...Multi-day moderate to heavy rain and high-elevation snow across the Alaska Panhandle beginning late this week through early next week... ...Overview and Guidance Evaluation/Preferences... Latest guidance continues to show a general theme of multiple fast-moving low pressure systems to track across the North Pacific and then through the Aleutians toward the Gulf of Alaska into the Alaska Panhandle. This would produce the most active weather from the Aleutians and surrounding waters to parts of the southern coast and Panhandle. The uncertainty displayed by the model spread continues to be on the timing of each individual weather systems traveling within the general west-to-east storm track. The ECMWF deterministic as well as the EC mean tend to adopt a faster forward motion and along a slightly higher latitude when compared with the GFS and CMC solutions. This discrepancy between the EC and GFS/CMC extends through the medium-range period for the Alaskan domain and vicinity. The WPC forecasts for Alaska's medium-range period for today were derived from 25% of the 12z ECMWF/00Z EC mean, 30% of the 12Z CMC/CMC mean, and 45% of the 12Z GFS/GEFS with higher percentages from the ensemble means toward the latter portion of the forecast period. This blend yielded a solution rather compatible with yesterday's WPC forecasts, only with a slightly faster forward motion for each of the cyclones moving along the general storm track. ...Weather/Hazards Highlights... A developing northeastern Pacific wave approaching Alaska Peninsula late on Friday will signal the beginning of a wet period for the Alaska Panhandle. A parade of Pacific cyclones that follow will bring a renewed round of moderate to heavy precipitation each new day for the Panhandle into early next week. Even though uncertainty regarding the timing of the arrival for the cyclones grows with time, the frequency of them will likely result in multiple days of moderate to heavy precipitation for the Panhandle. The larger and deeper cyclone that is forecast to move along the Aleutians this weekend is forecast to move more slowly when it reaches the Gulf of Alaska early next week. This will tend to prolong the precipitation already present across the Panhandle into midweek. Gales will be widespread from the Aleutians to the southern coastlines and into the Panhandle with this larger and deeper cyclone from the weekend into early next week. The next cyclone on the horizon appears to take a similar path and skirt along or just south of the Aleutians by midweek next week but perhaps at somewhat weaker intensity and smaller in size than its predecessor. Most of the southern part of the mainland into the Panhandle will likely see below normal highs during the period. Areas to the north may see more of a mix of above/below normal anomalies, with greater dependence on exact details aloft into the weekend. Eventual trend toward more agreeable mainland upper troughing by the first half of next week may support a cooling trend by that time if not earlier. Expect morning lows to be somewhat more above normal, but some modestly negative anomalies should spread from the southwest into the Interior late week into 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 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