Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 757 PM EDT Tue Oct 05 2021 Valid 12Z Sat Oct 09 2021 - 12Z Wed Oct 13 2021 ...Active pattern continues with periods of gusty winds and precipitation across southern Alaska... ...Pattern Overview... Progressive and energetic flow aloft will lead to multiple surface low pressure systems affecting portions of Alaska through the period. The first system in the Gulf of Alaska should be winding down at the start of the medium range period Saturday, but with lingering precipitation over the Panhandle and gusty winds over the Alaska Peninsula. Another low is then forecast to track into the Bering Sea Sun-Mon, and guidance has become more agreeable for a triple point low to form and deepen in the Gulf of Alaska around Tuesday. A third system could also emerge over the Bering Sea by Tue-Wed. Areas of enhanced precipitation and/or strong winds are likely with each system. ...Guidance/Predictability Assessment... Model guidance is fortunately in fairly good agreement throughout the period with the pattern described above. Deterministic and ensemble guidance show low pressure lingering along the Southcentral to southeastern Alaska coast over the weekend, which maintains continuity from previous forecasts. As the next mid-upper shortwave comes into the Bering Sea and produces a surface low early next week, only fairly minor timing and amplitude differences were seen through Monday. The main exception is the 12Z UKMET, which had a faster tracking shortwave that went against consensus, so it was not used today. 12Z deterministic models generally all showed a mid-upper low closing off temporarily in the Gulf of Alaska around early Tue, strengthening a surface low that was initially the Bering surface low pressure system's triple point. This stronger development was the main change to the forecast since yesterday, with a deeper surface low. Then the next system coming into the western Bering Sea Tue and tracking eastward Wed continues to show better than average agreement compared to typical late-period forecasts. Overall, the WPC forecast began with a 12Z ECMWF/GFS/CMC blend at the beginning of the period, adding some 12Z GEFS/00Z ECens mean to the blend as the period progressed, but only ended up with 30% means by the day 8 period since the deterministic guidance was fairly agreeable. ...Weather/Hazard Highlights... Precipitation is expected to continue over the Panhandle Saturday, as the initial surface low persists but weakens, while gusty winds could continue in the Alaska Peninsula in the trailing pressure gradient. Then it is becoming more likely that the next system in the series will spread precipitation and enhanced winds to the southwestern mainland early next week, with precipitation likely beginning Monday along the Gulf Coast as the low strengthens in the Gulf. The exact placement of the highest winds and heaviest precipitation will depend on the exact surface low track, however. Then yet another system tracking across the Bering Sea Tuesday into Wednesday could spread some precipitation and brisk winds to the Aleutians and the western mainland. Temperatures should generally be cooler than normal through the period for much of the southern part of the mainland and the Panhandle, particularly in terms of highs. For the northern two-thirds of the state, near average highs are forecast with a mixture of slightly below and slightly above normal readings through the first part of next week. Low temperatures are expected to generally be above normal for western and northern parts of Alaska. Tate Hazards: - Heavy precipitation across portions of mainland Alaska, Fri, Oct 8. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Fri-Sat, Oct 8-Oct 9. - High winds across portions of mainland Alaska and the Aleutians, Fri-Sat, Oct 8-Oct 9. 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