Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 606 PM EST Mon Jan 13 2025 Valid 12Z Fri Jan 17 2025 - 12Z Tue Jan 21 2025 ...Active pattern later this week/weekend for parts of western and coastal Alaska... ...General Overview... Active weather will continue late this week into the weekend for parts of the Aleutians, western 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 to displace/shift east strong ridging extending from the Gulf into Mainland Alaska. Another upper low/trough looks to edge south of the Aleutians and possibly into the Bering towards the end of the period. ...Model Guidance Assessment... The latest model guidance continues to show 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 this involves individual surface/triple point lows lifting towards the AK Peninsula to Southern Coast into this weekend, which may work to enhance additional winds/precip in some spots, depending on strength. Guidance agrees that one shortwave this weekend should act to briefly push upper ridging over the Mainland/Southeast eastward but should build back again ahead of the next trough into the Bering/Aleutians early next week. There is also a lot of uncertainty with the main and smaller scale surface lows with ensemble mean guidance showing a mean low over the Bering Sea, but individual models suggesting something closer to or south of the Aleutians. The WPC progs for today were derived from a general model compromise between the GFS, ECMWF, CMC, and UKMET for Days 4 and 5, gradually increasing the ensemble mean contribution for days 6 to 8. Overall, maintained fairly good continuity with yesterdays forecast. ...Weather/Hazards Highlights... Heavy precipitation will spread across South-central and parts of Southeast Alaska through the weekend as a broadening closed low expands eastward, shifting the atmospheric river from the Pacific slowly in that direction with time. Rain should linger across the Aleutians and southwest AK through the period. Recent model runs have also indicated moderate to heavy precipitation chances increasing for parts of western Alaska as well. Above normal temperatures will make rain the main precipitation type in southwest AK and for coastal locations, but wintry mixed precipitation and snow will be possible farther north and at elevation. Rain falling on top of snow could enhance snowmelt and lead to localized flooding concerns in some areas, such as Kodiak Island. 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. A lingering front and strong pressure gradient may make the Northern Slope breezy as well. Santorelli 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