Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 745 PM EDT Sun May 01 2022 Valid 12Z Thu May 05 2022 - 12Z Mon May 09 2022 ...Overview... The primary focus of the forecast will initially be on a compact but deep upper low over the eastern Bering Sea/eastern Aleutians late this week and a weaker feature over the Gulf of Alaska. There is uncertainty over how far east the Bering Sea low will progress after Friday but regardless, a moderate majority of guidance suggests that northern stream flow should interact with a mid-latitude Pacific system, ultimately bringing the latter on a track to the south of the Alaska Peninsula and perhaps near/into the Gulf of Alaska. Details of the system and any effects to its north are still fairly uncertain though. Mainland Alaska should see an ill-defined upper pattern, tending to favor weak ridging Thursday-Saturday and then possibly weak southwesterly flow over northern areas as a modest trough axis develops near the western coast. Arctic high pressure should gradually make its way into the Canadian Archipelago during the period. ...Guidance/Predictability Assessment... Latest guidance provides some common themes but there is enough spread to temper confidence in various details after about Friday. The first notable divergence in guidance involves the eastern Bering Sea upper low, with latest GFS runs already a bit west of the ECMWF/UKMET/CMC to start the period early Thursday. With time this difference leads to the GFS holding the feature over the eastern Aleutians to interact with the approaching Pacific system, in contrast to the others that progress it steadily eastward (albeit with variations in latitude depending on any interaction with a leading weaker low). Ensemble means generally lean toward their parent models. Interestingly the ECMWF/ECMWF mean still show enough lingering mean troughing/northern stream digging to the west to influence the Pacific system, leading to the ECMWF/GFS and their means depicting a similar overall pattern by late in the period. Recent GFS/GEFS trends have been toward the ECMWF/ECMWF mean idea. On the other hand the 12Z CMC/CMC mean suggest less stream interaction by mid-late period, leaving the Pacific system well to the southwest. For the purposes of a single deterministic forecast, preference favored the majority scenario for both the Bering Sea upper low and then the evolution that brings low pressure to the south of the Alaska Peninsula. This was achieved by way of a 12Z operational model composite early, followed by phasing out the CMC and trending the forecast toward an even blend of means (12Z GEFS/00Z ECens) and models (12Z/00Z ECMWF and 12Z GFS) by day 8 Monday. The new 12Z ECMWF mean and 18Z GFS offered no significant changes in continuity from their previous runs. ...Weather and Hazard Highlights... Upper lows over the eastern Bering Sea/Aleutians and farther east into or near the Gulf of Alaska, along with their surface reflections, may produce periods of precipitation from the Aleutians to the Panhandle late this week with most amounts on the lighter side. The Alaska Peninsula and vicinity could see some increase of moisture around late weekend/early next week with low pressure that may track to the south. Moisture could eventually extend eastward to the Panhandle. Track and timing of this late-period system and path of its moisture are still uncertain so confidence in specifics is fairly low. Mostly scattered and light precipitation is possible at times primarily over the southern half of the mainland. Temperatures should maintain a consistent pattern for most of the period, with below normal highs across the southern mainland and Panhandle as well as the North Slope, with moderately above normal highs over Interior areas. Morning lows will tend to have warmer anomalies, leading to more coverage of above normal readings. Sufficiently warm temperatures combined with the remaining snow pack could present flooding concerns across portions of the Yukon River Basin in eastern Alaska. 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