Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 606 PM EST Fri Dec 08 2023 Valid 12Z Tue Dec 12 2023 - 12Z Sat Dec 16 2023 ...Multi-day Heavy Precipitation and High Wind Threat from South-Central/Alaska Range to Southeast Alaska... ...Guidance Evaluation/Preferences... A wet pattern remains on the horizon for next week. Forecast spread has decreased from yesterday, bolstering forecast confidence to a degree for storms embedded within an active/blocky pattern for Alaska. The WPC Alaskan medium range product suite was primarily derived from a composite blend of the 12 UTC GFS/ECMWF/UKMET/Canadian valid for Tuesday-Thursday. Lingering differences and run-run continuity issues with smaller scale system interactions and stream phasing, along with uncertainty of block transition later next week/weekend, then seem to favors a quick transition to the 12 UTC GEFS/ECMWF ensemble means to mitigate variances as consistent with individual system predictability. This plan seems to offer a good forecast basis for the mid-larger scale pattern evolution, the main weather hazards and WPC product continuity. However in retrospect, a better guidance solution for these longer time frames might be a subset cluster of ensemble members that are slower to breakdown blocky flow that often tends to linger more than the bulk of guidance indicates. ...Weather/Hazards Highlights... An unsettling upper trough position should linger next week over the mainland as reinforced by less certain digging shortwave energies. This may lead to periods of light to locally enhahced snows over the mainland and windy conditions upstream from the Bering Strait into the Bering Sea. Meanwhile, a main storm genesis pattern will emerge just to the south of the state next week with the development and poleward track across the Gulf of Alaska to the mainland of a series of complex and deepened low pressure/frontal systems as stream flows uncertainly interact. The systems will offer a maritime to coastal high wind/wave threat. Deep layered and long fetch moisture will also feed inland by enhanced wind flow around these storms, with main focus over South-Central/Alaska Range through Southeast Alaska. Expect a multi-day period with periodic surges of heavy precipitation in the form of coastal rains with potential runoff issues due to the protracted accumulation that will also be a factor for heavy inland/terrain/mountain snows. Additionally, gusty terrain enhanced winds expected for this region along with gap and downslope Chinook winds to the lee of the Alaska Range into the southern Interior next week. 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