Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 759 PM EDT Fri Sep 23 2022 Valid 12Z Tue Sep 27 2022 - 12Z Sat Oct 01 2022 ...Heavy rainfall expected across the Panhandle and the coastal Kenai and Chugach Mountains through the upcoming workweek with another big storm possible in the Bering late next week... ...Synoptic Overview... The upper level pattern remains unsettled, but very slow changing across Alaska through much of the upcoming workweek. The large longwave trough remains essentially stationary. By late next week we could be seeing another big storm making its way into the Bering. As a result, the upper level pattern seems to very slightly shift westward with time, meaning the upper level trough axis moves from over the west coast of the state to more over the central Bering by next Friday. This shift could be the result of the newly forecast large surface low expected in all the major deterministic models by Thursday and Friday. Outside of that, expect more of the same...with the upper level trough largely stationary, expect periodic waves of energy to rotate around the periphery of the longwave trough, resulting in multiple lows traversing largely west to east across the Bering and into the Gulf. Then before the low can completely dissipate over interior Alaska, the next one follows close on its heels, resulting in very little respite between storms. Beginning on Tuesday morning, a low over the Eastern Aleutians tracks into Bristol Bay by Wednesday morning, weakening as it moves on that track. The leading front will cause a triple point low to form on Thursday morning east of Kodiak, which is a very common pattern. That secondary low will move into the northern Gulf by Friday morning, though should remain a weak low. Impacts will be primarily with the initial low over the southern Bering which moves into Bristol Bay and then into interior Alaska. Along this track, expect gusty easterly winds ahead of the low center, and through the gaps, especially the Barren Islands and some elevated winds through Turnagain Arm. A secondary weak low will track out of the Kamchatka Peninsula Wednesday morning, but very quickly weaken as it moves along the Aleutians through Thursday. No major impacts are expected from this system. On Friday into Saturday, all eyes turn to a third and potentially strongest low of the bunch. This low may follow a track at least similar to the remnants of Merbok last week. There is significant uncertainty on the details, mainly because this storm is still 6-7 days away and a lot can change in the models. Consider that 24 hours ago, this low was a very weak disturbance tracking along the Aleutians. That said, however, it is quite notable that all of the major deterministic models, and their ensemble clusters are now depicting at least a strong low tracking somewhere in the central to eastern Bering around that same time frame. As of now, none of the guidance suggests this storm getting as strong as Merbok was, but nonetheless a storm following a similar track so soon after that storm, while recovery efforts are still ongoing, may exacerbate the impacts that otherwise may not have been as widespread. Stay tuned. ...Guidance/Predictability Assessment... The guidance suite remains in good agreement through about Day 6/Thursday. This increased confidence on the track of the low over the eastern Aleutians/AKPEN on Tuesday morning tracking northeast into Bristol Bay and into interior Alaska, with a triple point low developing over the Gulf east of Kodiak and tracking into the northern Gulf. Very little about this storm and its triple-point low have changed in past 24 hours since the previous update. Once again the biggest change, and unfortunately the most impactful, remains the potential for a strong storm moving out of the North Pacific, across the Western Aleutians, and moving somewhere in the central Bering by Saturday morning. There is a large model spread on the track of this low, which as mentioned, is very common for storms this far out in the guidance. There is also little run-to-run consistency with this storm, as just yesterday it was non-existent in any of the models, and today many of them now show this strong storm and all depict it taking a similar track. Elsewhere, the leading front for the triple point low in the Gulf Thursday will keep conditions unsettled across the Panhandle right through Friday, with perhaps a break in the weather come next weekend as the big storm absorbs any smaller lows around it. For interior and northern Alaska, little has changed, as the remnant lows that move into that region from the south largely stall out and dissipate over the interior each day that week. No major impacts are expected since the storms will be in a weakened state by the time they get there. ...Weather/Hazards Highlights... Southern portions of Alaska are expected to remain rather active during the medium range period as multiple disturbances round the base of a potent upper-level low in the eastern Bering Sea before a potentially more robust system impacts the Aleutians by the end of the week. Starting on Tuesday, A low tracking the Eastern Aleutians moves into southwest Alaska by Wednesday is likely to bring an additional round of heavy precipitation to the south-central coastline and Panhandle through the end of the week. A very strong area of low pressure is possible across the southern Bering Sea and Aleutian islands Friday into Saturday. The main impacts at the moment appear to be associated with high winds, heavy precipitation, and coastal flooding, potentially in many of the same areas impacted by Merbok last week. Wegman Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue, Sep 27 and Thu-Fri, Sep 29-Sep 30. - Heavy precipitation across portions of mainland Alaska, Wed-Thu, Sep 28-Sep 29. - High winds across portions of the Aleutians, Fri, Sep 30. 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