Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 621 PM EST Thu Nov 19 2020 Valid 12Z Mon Nov 23 2020 - 12Z Fri Nov 27 2020 ...Strong system near Kodiak and into the Gulf Monday... ...Overview and Guidance/Predictability Assessment... Active pattern will see two robust systems of different flavors impact Alaska. Lead system will deepen to around 960mb near Kodiak by 12Z Mon before slipping eastward through the southern Gulf then across the southern Panhandle into Canada. The GFS finally came around to the other solutions yet still was displaced a bit to the south. Blend of the 12Z ECMWF/UKMET/Canadian offered a good starting point with that system but the GFS was acceptable elsewhere. Next system will move through the Bering from the east, with added southern stream energy. GFS was again perhaps too aggressive with this influx from the south, and took that low as the new dominant low toward Kodiak into the Gulf. However, ongoing model/ensemble consensus is to maintain that low as only a weaker feature, allowing it to be absorbed into the larger Bering system. That has repercussions on the flow over northern Alaska where the GFS would allow ridging to maintain itself whereas the other guidance shows lower heights chipping away at the ridge (which will be already weakening anyway). Therefore, given the recent poor track record of the GFS opted to stay with the larger ECMWF/Canadian-led cluster which was supported by at least some of the GEFS members (and mostly ECMWF members) and continues continuity as well. This would take a triple point low into the Gulf around next Wed/Thu as the old parent low dissipates (slowly) in the central then eastern Bering. A weaker front or two may rotate around the larger Bering circulation as well, again depicted on the surface progs. Trended toward more ensemble weighting by next Wed/Thu (about 80%) to account for detail disagreements in the ECMWF/Canadian and their recent runs. ...Weather/Threats Highlights... Mon-Tue system has the potential for widespread modest rain/snow along the eastern Aleutians, southwest coastal mainland, and over Kodiak to the southern Kenai along with breezy/windy conditions (40kts+). Storm track may force much of the precipitation to just the southern Panhandle to British Columbia, though it will likely churn up some large waves over the Gulf (see the Ocean Prediction Center over the next few days for more information). Next system in the Bering may have a less favorable moisture source but could still bring some rain/snow to the island chain on southwesterly flow ahead of the front. Some precipitation is forecast to expand over western/southwestern areas and Southcentral next Wednesday but at this point it is unclear how much enhancement there will be based on southern moisture influx. This should spread eastward across the Gulf into the Panhandle around next Thursday. Temperatures will remain well above normal along northern areas thanks to upper ridging and above normal lower level temperatures, though they should trend a bit back toward normal later next week. Southeastern third of the mainland into the Panhandle will see near to below normal temperatures. Fracasso Hazards: - Heavy precipitation across portions of mainland Alaska, Wed, Nov 25. - Heavy precipitation across portions of the Alaska Panhandle, Mon, Nov 23. - High winds across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Nov 23-Nov 24. - High significant wave heights for coastal portions of the Alaska Panhandle, Tue, Nov 24. Additional 3-7 Day Hazard information can be found on the WPC medium range hazards 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