Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 627 PM EST Wed Dec 13 2023 Valid 12Z Sun Dec 17 2023 - 12Z Thu Dec 21 2023 ***Heavy Snow and coastal rain for south-central Alaska this weekend, and windy for the Aleutians*** ...Guidance Evaluation/Preferences... The 12Z model guidance suite has a good overall depiction of the synoptic scale pattern across the Alaska domain going into the weekend, with a broad upper low situated over the Bering and two well-defined shortwaves crossing south of the Aleutians and into the Gulf region. Going into Monday, the GFS becomes more progressive with the low over the southern Gulf, but still close enough to the consensus to merit a multi-deterministic model blend. Looking ahead to the middle of the week, models still agree well on a closed upper level gyre over the southern Bering, but differ more with shortwave passages across the North Pacific and into the Gulf region, which is typical for this time frame. The GFS becomes notably faster with the trough crossing the Gulf next Thursday. The use of the ensemble means was increased to 40% by that time, while tapering down the GFS. ...Weather/Hazards Highlights... The most active weather during this forecast period is expected to be across the southern coastal areas and extending westward across the Aleutians. Heavy snow is likely for the coastal mountain ranges extending from the Kenai Peninsula eastward to the St. Elias Mountains for the upcoming weekend with moist onshore flow, and several feet of additional snowfall accumulation is likely for these areas. Right along the coast, there may be just enough warm air to support either a cold rain or a rain/snow mix, and this could also be heavy at times. Winds will likely be making weather headlines across the eastern Aleutians and the Alaska Peninsula going into early next week with a potent Bering Sea low pressure system developing and a strong pressure gradient south of it. Very high surf and possible coastal flooding are also hazards that could be realized. This same low will likely be associated with warm air advection snow across portions of the western mainland/Interior. Additional heavy snow is likely for the south-central mountains by midweek as well. In terms of temperatures, there will likely be a slow moderation trend in the bitterly cold weather across the northern third of the state, with highs getting closer to zero by Tuesday and Wednesday. The coldest readings are expected for the North Slope and the Yukon Flats Sunday morning, with some -20s expected. For the southern coastal cities, expect highs to generally be in the 30s, except 20s for the greater Anchorage area. Hamrick 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