Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 559 PM EST Wed Nov 27 2024 Valid 12Z Sun Dec 1 2024 - 12Z Thu Dec 5 2024 ...General Overview... A blocky upper level flow pattern is expected to be in place across the Alaska domain for the weekend after Thanksgiving, with a cut-off upper high over eastern Siberia. A well defined upper low pinches off from the broader trough axis that will be in place across over northwestern Canada Saturday, and then retrogrades southwestward towards the southern Bering and just north of the Aleutians around the upper high by Monday morning. This upper low is expected to spur surface cyclogenesis south of the Alaska Peninsula by the middle of next week. Across mainland Alaska, an arctic air mass will be in place, and this should gradually modify some going into next week. A +PNA pattern is expected to be in place across western Canada with an upper ridge axis in place across British Columbia. ...Guidance Evaluation/Preferences... The 12Z model guidance suite features reasonably good synoptic scale agreement across the Alaska domain on Sunday, with good overall clustering with the upper low crossing southwest across Alaska through the weekend. The models are also in good agreement with the upper high situated across the western Bering and far eastern Siberia, and this high then weakens and moves westward for early in the week. Similar to yesterday, the region with the greatest model differences is across the Gulf region and the timing of multiple shortwave impulses around the main upper level low that will affect the southeast portion of the state. Model differences become more widespread and significant going into next Wednesday-Thursday, and thus the ensemble means accounted for about half of the model blend by that time. ...Weather/Hazards Highlights... Periods of moderate to heavy rain are expected to make weather headlines across the southeast Panhandle for the first few days of December as a potential atmospheric river event sets up and brings several inches of rainfall across the windward terrain. This may lead to enhanced run-off and rises on area rivers. The heaviest rainfall is likely to be on Monday, and mainly near the Ketchikan region. Given the milder conditions expected here, snow levels will be higher and most population centers will get mainly rain. Additional rainfall is expected going into the middle of the week as well. Farther west, heavy precipitation is possible for the windward facing terrain of the southern Alaska Peninsula and the Kenai Peninsula, particularly during the middle of next week. Elsewhere across the state, the majority of the mainland should remain dry north of the Alaska Range. There may be some gap winds that develop across portions of the Alaska Peninsula and points eastward for the first half of the week, depending on how the surface lows evolve to the south. Frigid temperatures are expected for much of the Interior and the Brooks Range, with overnight lows dropping into the -10s to -20s through Monday, and highs only recovering about 10 ten degrees from those lows. The good news is a moderating trend is likely to commence going into early to middle next week as the upper ridge axis from western Canada tries to build in, and more of a maritime influence develops across southern Alaska. 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