Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 645 PM EST Fri Nov 11 2022 Valid 12Z Tue Nov 15 2022 - 12Z Sat Nov 19 2022 ...Overview... After a short-lived upper trough passes across the mainland on Tuesday, the pattern across most of the state will be dominated by upper ridging and surface high pressure moving in. This should direct a couple of low pressure systems to the west of the mainland, with an initial one tracking across the western Bering Sea and eastern Siberia Tuesday-Wednesday and another crossing the Aleutians around early Wednesday and continuing northward across the Bering Sea. These lows may cause gusty winds and some precipitation over the Aleutians and into northwestern portions of the mainland. By late in the week, the ridge pattern generally holds on but some shortwaves and surface lows could provide some rounds of precipitation to the Aleutians and Alaska Peninsula. ...Guidance/Predictability Assessment and Preferences... Model guidance begins in reasonably good agreement at the start of the forecast period Tuesday, indicating a transient upper trough across the mainland with a deeper upper low well south in the Pacific, with an upper ridge starting to build behind those features. Models also show good consensus with the ridging building into the state for midweek and beyond. Less certain in the guidance are the exact tracks of surface lows accompanying shortwaves that look to track on the western side of the ridge potentially across the Aleutians and the Bering Sea. While the model differences are somewhat minor for a medium range Alaska forecast, any west-east spread could cause impactful differences in gusty winds and precipitation across the Aleutians and western mainland. Specifically, the initial low looks to have a northeasterly track across eastern Siberia and toward northwestern Alaska but with the center of the low staying west. Then models have started to show better agreement today with a second low with potentially tropical origins that tracks north/northeastward over the Aleutians and into the Bering Sea, not interacting with a low upstream in the Pacific like many models showed yesterday. The 06/12Z GFS runs and the 12Z ECMWF in particular had good consensus with the placement of the surface low 12Z Wednesday over the Aleutians, but spread increases for both position and timing of the low moving northward, indicated by the individual models and the elongated nature of the ensemble means. There also may be downstream consequences for these shortwave and surface low differences as they may round the ridge, shown by GFS and CMC runs suppressing/flattening the northern side of the ridge across the Arctic in the latter half of next week, with less evidence for this in the ECMWF and the ensemble means that keep strong ridging. Other than that, there is some typical spread in potential upper and surface low features in the Pacific likely south of (but potentially nearing) the Aleutians. Thus the WPC forecast utilized a fairly typical model blend consisting of a multi-model deterministic blend favoring the GFS and ECMWF early in the period, with gradual increasing of the weighting of GEFS/EC ensemble mean components to a little over half by days 7-8 given the increasing model spread. ...Sensible Weather and Potential Hazards... While heavier precipitation amounts have phased into the short range period, lingering modest precipitation could continue across parts of the Panhandle through Tuesday given Pacific moisture streaming in, with snow possible in higher elevations and rain near the coast. Some light precipitation is also possible into the mainland with the upper trough moving quickly through. Then the northwestern mainland could be affected with precipitation and moderate to high winds around Tuesday-Thursday depending on the exact track of the eastern Siberia and Aleutians to Bering Sea storm systems. A high winds hazard area was added into WPC's medium range hazards product today for western portions of the Seward and Lisburne Peninsulas for this potential for onshore flow. Generally precipitation chances are forecast to increase across the Aleutians beginning midweek, but with considerable uncertainty in the details of amounts and timing of the rounds of precipitation. After some colder than average temperatures are possible for the western mainland Tuesday, the upper ridge pattern will lead to above average temperatures across much of the state for the period. The North Slope looks to see the highest anomalies above normal. Temperatures in Utqiagvik for example may approach around 30F around midweek despite polar night approaching. The rest of the mainland is also likely to be above normal through late week, with more of a mix of above/below average temperatures for the Panhandle. Tate Hazards: - High winds across portions of mainland Alaska, Tue-Thu, Nov 15-Nov 17. 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