Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 639 PM EDT Wed Oct 09 2024 Valid 12Z Sun Oct 13 2024 - 12Z Thu Oct 17 2024 ...Deep Gulf of Alaska Storm to bring strong winds, heavy rain and maritime threats Friday into Monday... ...Heavy snow threat for the East-Central Brooks Range this weekend... ...Overview and Guidance Evaluation/Preferences... Predictability is above normal through medium range time scales and shows continuation of a highly active storm pattern. Guidance generally agrees with development of yet another major storm with high winds/waves from the Bering Sea to the Gulf of Alaska along with multi-day heavy precipitation and runoff threats for Southern to Southeast Alaska late week into early next week. There is also a growing signal upstream supporting a deepened and moist extratropical low track toward/south of the Aleutians to the western Gulf of Alaska next week associated with current West Pacific Barijat. The North Slope/Brooks Range also has a weekend window for some enhanced winds and snowfall with lifting system energies. Prefer a composite of reasonably clustered guidance of the 12 UTC GFS/ECMWF/UKMET/Canadian Sunday-Tuesday before blending in ensembles as forecast spread slowly grows. Manual adjustments will ensure sufficient system depth given closed upper trough support, tropical origins and to offset weakening inherent to a blending process. ...Weather/Hazards Highlights... The major storm reaching the western Gulf of Alaska by the end of this week will produce a broad area of high winds from the eastern Bering Sea/Aleutians to the Northeast Pacific/Panhandle. Highest wind speeds should be over the weekend, in the northerly flow over the eastern Bering/Aleutians and in easterly/southeasterly flow near the Southcentral coast and Panhandle. Significant waves will also present quite a wind/wave threat for maritime interests. Meanwhile, the eastern side of the storm's circulation will bring a multi-day period of heavy precipitation to the southern Alaskan tier through Southeast Alaska, with the best atmospheric river signal evident over the weekend when precipitable water values should be most anomalous. Both winds and precipitation should trend less extreme with time, though mean troughing aloft over parts of the mainland and lingering low pressure near Kodiak Island may support southern coast/Panhandle precipitation through the first half of next week. The Days 3-7 Hazards Outlook reflects the most confident areas for high wind and heavy precipitation threats. Farther north, potent shortwave energy and an associated surface low breaking off from the northern side of the western Gulf storm will likely produce an area of heavy snow across parts of the northern mainland this weekend that has also been added to the WPC Hazards Outlook. The strongest snow signal seems to be as moisture feed over the still unfrozen Arctic Ocean feeds inland in enhanced windy flow across the North Slope and into favored central to eastern Brooks Range terrain. Upstream, another organized storm is expected to develop and track along/just south of the Aleutians early next week before feeding into the western Gulf of Alaska mid-later next week. This deepened extratropical low is associated with current West Pacific Tropical Storm Barijat. Details should further emerge over the next couple of days for more specific WPC Hazards Outlook consideration, but suspect the highly supportive nature of yet another closed upper low/trough along with tropical system origin would most likely support potential for high winds/waves and swirling moderate rains across the broad region. Schichtel 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