Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EST Tue Dec 31 2024 Valid 12Z Sat Jan 4 2025 - 12Z Wed Jan 8 2025 ***Heavy precipitation expected early next week for the eastern portion of the Alaska Peninsula into the Kenai Peninsula*** ...Overview with Guidance Evaluation and Preferences... The forecast period begins on Saturday with an upper trough draped across the Alaska mainland, and a closed upper high over eastern Siberia and a building ridge axis near British Columbia. Meanwhile, a broad upper level low situated just south of the central Aleutians should be anchored in place through the weekend, and multiple low pressure systems are forecast to pivot around this and cross the Gulf and affect the southern mainland, with the strongest system expected to arrive late on the 5th and into the 6th with high winds and heavy precipitation. going into next week, a +PNA pattern develops with a major western Canada upper ridge developing, and a general trough across the Bering into the western Gulf. The model guidance is initially in good overall synoptic scale agreement across the domain Saturday, with some timing differences in the arrival of shortwave perturbations across the Gulf. Going into Sunday, the GFS becomes stronger with a lead surface low entering the Gulf, and then with the main event arriving Monday, the ECMWF/CMC are faster than the stronger GFS, and the CMC is weaker. Going into Tuesday and beyond, the CMC brings in a third system across the Gulf, but this hardly has any support from the GFS/ECMWF and limited support from the ensembles, so the forecast was hedged more in the direction of the GFS/ECMWF and their respective ensemble means for the second half of the forecast period. ...Weather/Hazards Highlights... Strong northeasterly flow is expected across the Bering Sea and through the Aleutians, with increasing chances of heavy precipitation moving into the eastern Aleutians and the Alaska Peninsula by late Sunday. For early next week, the heavy precipitation should gradually move northward across the eastern portion of the Alaska Peninsula and Kenai Peninsula. There is still some uncertainty on the details of the track and intensity of smaller-scale cyclones coming up from the south, leading to differences on the details in the timing of the heavy precipitation at this point in time. However, there is the potential for several inches of rain near the coast and multiple feet of snow for the coastal mountains as the atmospheric river of moisture is directed towards the coast. The persistent east to northeasterly flow being fed by a strong surface high pressure system centered over the Arctic Ocean (with central pressure possibly above 1050 mb) late this week will keep temperatures below normal for much of mainland Alaska for the weekend. Minimum temperatures are likely to be in the -30s over the Yukon Flats and adjacent portions of the eastern mainland. Above normal temperatures initially confined farther south across the Alaska Peninsula and the Aleutians will gradually spread toward the north and east into mainland Alaska early next week as the upper ridge builds over western Canada and the arctic air mass modifies. 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