Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EDT Wed Oct 05 2022 Valid 12Z Sun Oct 09 2022 - 12Z Thu Oct 13 2022 ...Heavy rainfall and elevation heavy snow threat for South-central to Southeastern Alaska this weekend to return next midweek in stormy pattern... ...Bering Sea storm to impact Western/Southwestern Alaska Monday... ...Guidance/Predictability Assessment and Weather/Hazards Highlights... The 12 UTC GFS/ECMWF/UKMET/Canadian solutions seem well clustered into Sunday and a composite blend favoring these models seems to offer a good basis for the forecast. Recent runs of the GFS have come in line with more amplified mainland to Gulf of Alaska upper trough development. This will offer a maritime threat along with a multi-day threat through Sunday for heavy rainfall, enhanced gap winds and a terrain enhanced moderate to higher elevation snowfall/snowstorm across a cooling south-central and southeastern Alaska given longer fetch moisture inflow with Gulf of Alaska system genesis under favorable upper support. Enhanced rains will work across the Aleutians with Bering Sea storm approach Sunday. Guidance remains varied with storm details, but the cluster of model and ensemble low pressure centers into early next week over the Bering Sea has trended significantly farther north and potentially much deeper with a dynamic low. There is now a stronger guidance signal to intensify the system with track from the western Pacific along with potent upper jet support from off east Asia. The 12 UTC Canadian and especially the 12 UTC GFS offer a progresisve and deep storm compared to recent ECMWF runs. However, the 12 UTC ECMWF has trended slightly faster across the Gulf into southwest Alaska Monday. WPC progs depict a northward shifted and deeper storm slamming inland from the Bering Sea compared to yesterday. This system offers a maritime threat and is expected to bring lead enhanced precipitation inland across western/southwest Alaska Monday along with a swath of wrapping high winds. Individual system timing and emphasis differences become more problematic into next midweek in amplifying flow. However, model and ensemble solutions still favor a similar patern evolution aloft into and highlight development of an amplified upper trough from the Bering Sea through the Aleutians and amplified upper ridging building over the central to eastern Gulf of Alaska. There remains a signal to monitor for the tapping of additional mid-latitude Pacific system energy/moisture that could fuel another threat for heavy precipitation back into south-central to southeastern Alaska at these longer time frames. The WPC medium range product suite was derived from the still broadly compatible 12 UTC GFS/ECMWF/Canadian and GEFS/ECMWF ensemble means. Manually adjustements were applied to blend output to mitigate some system weakening inherent to the blending process given favorable upper support and an emerging flow channel to the state in between the upper trough/ridge couplet. Schichtel Hazards: - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Oct 8-Oct 9. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Tue-Wed, Oct 11-Oct 12. - High winds across portions of mainland Alaska, Mon, Oct 10. 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