Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 747 PM EDT Sun Mar 16 2025 Valid 12Z Thu 20 Mar 2025 - 12Z Mon 24 Mar 2025 ...Overview... From late this week into the weekend, the best guidance cluster offers good continuity for significant features with only some detail refinements. Continue to expect southerly flow or some degree of upper ridging over the mainland while an upper low wobbles over/near eastern Siberia. A trough axis should extend southeast near the southwestern mainland coast. Meanwhile a leading system should track from just south of the Alaska Peninsula into the Gulf, followed by an elongating system tracking a ways south of the Aleutians and reaching into the northeastern Pacific. These systems will tend to keep the southern coast and Panhandle unsettled during the period with some periods of brisk winds over the Alaska Peninsula and Aleutians as well. Ridging over high latitudes of the Arctic will help to maintain brisk easterly winds across the North Slope. The forecast pattern evolution should yield near to above normal temperatures over most of the state but the nearby upper trough should keep far western areas relatively colder. By Sunday-Monday the pattern looks to become more amplified as a ridge builds into the Aleutians and Bering Sea while pushing the persistent trough into the western mainland. ...Model guidance and predictability assessment... An average of 12Z models provided good continuity for the system forecast to be just south of the Alaska Peninsula as of early Thursday. Machine learning (ML) models still hint at the potential for slightly faster eastward timing, so such a trend is worth monitoring. Uncertainty over potential frontal wave development to the east by Friday complicates the forecast detail-wise, but the general forecast of low pressure over the Gulf looks good. 12Z/18Z GFS runs may be a little too southward and slow to open the upper low by Friday. The general forecast remains on track for low pressure to the south of the Aleutians and Alaska Peninsula by Friday-Saturday, with the system likely stretching out southwest-northeast as the supporting upper low opens up/elongates. Dynamical guidance suggests that leading frontal waviness south of the Alaska Peninsula (and perhaps another wave to its east) should be what ultimately lifts into the northeastern Pacific, while ML guidance and dynamical ensemble means keep the parent low and leading wave(s) closer together. Either way, ML models and dynamical models/means average out fairly close for strength from late week into the weekend. This is also the case toward Sunday-Monday as low pressure slowly weakens while most likely curling into the Gulf in response to the upper trough just to the west. ECMWF/CMC runs and their means plus the 12Z ICON keep the eastern Siberia upper low somewhat south of the GFS/UKMET late this week into the weekend, with ML models showing some spread as well. Persistence leans more toward the ECMWF cluster into Saturday. By Sunday-Monday some guidance has been suggesting that flow underneath the low may dig in response to a building upstream ridge. Dynamical models have varied in the end result. Solutions include forming a separate upper low that drops southward over the eastern Bering Sea/southwestern mainland, maintaining the initial low and pulling it southward, or just a sharpening open trough. The ensemble means and ML models favor an open trough so prefer tilting the forecast in that direction until embedded details become more agreeable. This favors tempering the deeper upper lows seen in the 12Z ECMWF/CMC. 12Z/18Z GFS runs represent slightly deeper versions of the trough scenario and ultimately close off a less deep upper low after early Monday. Farther west over the Aleutians by next Monday, ML models offer strong support for the axis of the building deep-layer ridge to reach east of 180 longitude while the upstream surface gradient reaches into the western Aleutians. This recommends a solution closest to recent ECMWF/CMC runs and their ensemble means versus the farther west GFS/GEFS. However consensus suggests that the 12Z ECMWF is too far east with its deep surface low that tracks near the western Aleutians, instead favoring a track closer to Kamchatka. Guidance preferences early in the period favored a blend consisting of 40 percent 12Z ECMWF with the rest evenly split among the GFS/CMC/UKMET. Day 6 Saturday started to add a small component of the 12Z CMCens/00Z ECens means. Then Days 7-8 Sunday- Monday split ECMWF input between the 12Z/00Z runs due to lower confidence aspects of the 12Z run while increasing those means to 40-50 percent total weight. ...Sensible weather and potential hazards... The southern coast and Panhandle should see unsettled weather for most of the period. Some localized enhancement of precipitation will be possible but guidance does not suggest heavy totals on an organized scale. Late this week a system drifting east from just south of the Alaska Peninsula as of early Thursday, along with possible frontal wave development to the east, will support this activity. Then one or more surface waves lifting into the northeastern Pacific (while previously keeping most precipitation south of the Aleutians farther west) and eventually the Gulf of Alaska should maintain chances for precipitation during the weekend and into the start of next week. It will still take a while to resolve specifics due to the low-predictability nature of the small-scale surface lows. Flow behind the leading system and then the North into Northeast Pacific low pressure may produce periods of brisk to strong northerly winds over the Aleutians and into the Alaska Peninsula. Portions of the western/southwestern mainland may see light/scattered snow late week into the weekend. Flow around high latitude Arctic high pressure will maintain brisk to strong easterly winds across the North Slope on most days. Returning to the Aleutians, a surface ridge should bring more tranquil conditions from west to east by Sunday-Monday but southerly winds should strengthen over the western Aleutians by Monday ahead of low pressure forecast to track near Kamchatka. Nearby upper troughing with an embedded low should keep temperatures somewhat below normal toward the western coast of the mainland. The below normal anomalies should gradually push eastward by Sunday-Monday in line with gradual progression of the trough. The remainder of the mainland should trend somewhat warmer with near to above normal temperatures. Expect warmer anomalies for morning lows relative to those for daytime highs. The Panhandle should see near to below normal highs but with above normal morning lows. Rausch 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