Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 432 PM EST Wed Jan 15 2025 Valid 12Z Sun Jan 19 2025 - 12Z Thu Jan 23 2025 ...Stormy pattern from Western Alaska through the Alaskan southern tier... ...General Overview... Stormy weather will continue through the upcoming holiday weekend into next week for parts of the Aleutians, Northwest/Western/Southwest Alaska, and the Southern Coast with plenty of onshore flow ahead of mean troughing through the Aleutians and Alaska Peninsula. A couple of shortwaves rotating through the base of this trough will lift across western Alaska, eventually working into strong ridging extending from the Gulf into Mainland Alaska. Another deepened upper low/trough looks to amplify across the Aleutians and into the Bering Sea next week to renew a stormy flow track conduit into these regions again with the rebuilding of the downstream upper ridge next week. ...Model Guidance Assessment... Latest models and ensembles generally continue a recent trend for relatively good agreement on the overall synoptic pattern, but plenty of uncertainty in the details. Much of the uncertainty surrounds smaller scale shortwaves rounding through the base of the larger scale trough over the Bering/Aleutians and as energies lift poleward on the western periphery of an ambient and amplified blocky ridge downstream up over the mainland. This includes individual surface/triple point lows lifting towards the AK Peninsula to Southern Coast into this weekend, which will work to enhance local winds/precipitation. The bulk of guidance agrees that one shortwave this weekend should act to briefly push upper ridging over the Mainland/Southeast eastward to a degree, but should build back again ahead of the next trough into the Bering/Aleutians early next week. This pattern may generally repeat into mid-later next week, albeit with less amplitude. Again prefer today a composite of reasonably clustered larger scale 12 UTC ECMWF/UKMET/Canadian guidance to provide maximum detail as consistent with predictability Sunday-Monday. The 12 UTC GFS seems to crash energy too much into the ambient blocking upper ridge versus running system energies more up the periphery. Opted to switch to best compatible GEFS/ECMWF/Canadian ensemble means guidance amid slowly growing forecast spread through later time frames. This maintains good WPC product continuity. ...Weather/Hazards Highlights... Heavy precipitation/winds will spread across South-Central and parts of Southeast Alaska through the holiday weekend as a broadening closed low expands slowly eastward, shifting the atmospheric river from the Pacific slowly in that direction with time as tempered by the blocking ridge. The stronger wind flow should also work inland and be enhanced from terrain up through/over the Alaska Range. Rain should linger across the Aleutians and into southwest AK through the period. There is now a stronger signal for moderate to heavy snow/blowing snow and high wind chances increasing for western/Northwest Alaska as well into this weekend, and to a lesser extent the Interior. Above normal temperatures will make rain the main precipitation type in southwest AK and for coastal locations, but wintry mixed precipitation and snow is likely farther north and at elevation. Rain falling on top of snow could enhance snowmelt and lead to localized flooding concerns in some areas. The strong nature of the low will also likely produce strong gusty winds from the Aleutians to western Alaska across the Bering Sea and Bering Strait up through the western/Northwest AK coast. A lingering front and strong pressure gradient may make the Northern Slope breezy as well. 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