Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 732 PM EDT Sun Sep 08 2024 Valid 12Z Thu Sep 12 2024 - 12Z Mon Sep 16 2024 ...Overview... As the medium range period begins Thursday, an upper trough will be pushing across the Mainland, which along with a Gulf surface low should spread moderate to heavy rain to southeastern parts of the state. Upper ridging is forecast to push through behind this trough and in response to additional energy and troughing coming into the Bering Sea late week. These upper and surface lows in the Bering gradually moving east will promote increasing precipitation chances across the Aleutians late week, spreading into western and central parts of the Mainland into next weekend, and affecting the Panhandle into early next week. ...Guidance Evaluation/Preferences... Recent model guidance continues to show general agreement with the large scale features of note. A stacked upper/surface low is pretty agreeable in the Gulf of Alaska Thursday and moving east into early Friday, so a multi-model blend worked well. As this upper trough exits, overall ridging looks to press east from the eastern Bering Sea/western Mainland Friday across the Mainland Saturday. Possible shortwaves moving around the ridge are uncertain. The non-NCEP models from 12Z indicate a shortwave on the northern side of the ridge into the western Mainland around Friday, enough to suppress the ridge a bit, with the CMC most aggressive, while GFS runs do not show as strong of a feature and it pushes more northward. Having some shortwave seems reasonable but it is quite shallow in the WPC 500mb heights blend. Meanwhile, broad energy and troughing are likely across the Bering Sea, gradually tracking east as the period progresses. Models show better agreement today for one main upper low within the trough moving from Kamchatka toward the Bering Strait Friday-Sunday and likely weakening as it does. There has also been a trend for the associated surface low to weaken as it tracks east, lessening concerns for significant high winds to affect the western coast at least in this cycle. These features generally press east toward the state into early next week, while another upstream low may come in and affect the pattern but with more considerable spread by next Monday. The WPC forecast was based on a blend of the 12Z deterministic models early, with increasing proportions of the GEFS and EC ensemble means as the period progressed to half means by Day 8. ...Weather/Hazards Highlights... The first trough and Gulf surface low could continue to spread notable precipitation from around Prince William Sound to Yakutat and the northern Panhandle on Thursday, though gradually trending down compared to the short range period. Lingering snow is possible on the backside of the low into the Alaska Range, with lighter precipitation to the north in central/eastern parts of the Mainland. Then as the broad upper trough and surface low pressure system get established in the Bering Sea, precipitation is likely to affect much of the state, moving from west to east with time. Precipitation is forecast for the Aleutians on Friday, moving into the Alaska Peninsula/western Coast late Friday or Saturday, and continuing across the state to focus in Southcentral Alaska for the weekend and then into Southeast Alaska early next week. The current forecast is for moderate to locally heavy rain amounts for coastal/lower elevation areas and some snow in the higher elevations. With low pressure in the northern Bering, there may still be some chance for high winds and potentially some minor coastal flooding along the western coast, but impacts do not look too significant especially given the trend toward a weaker low. Will continue to keep an eye on those potential threats. High temperatures should mostly be in the 50s across lower elevations of the state late this week, perhaps warming a few degrees into the weekend and next week. This is generally near to slightly below normal for highs. However, the North Slope with highs in the 40s will be above normal especially this weekend. Prevalent clouds and precipitation will favor mostly above normal morning lows, aside from a round of slightly below average lows tracking across the Interior Thursday-Saturday. Southeast Alaska may see a mix of below and above average lows depending on the day but with mostly below normal highs. Tate 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