Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 733 PM EDT Mon Mar 09 2020 Valid 12Z Fri Mar 13 2020 - 12Z Tue Mar 17 2020 ...Overview and Guidance/Predictability Assessment... While the occasional model run has waffled a bit in one way or another, the general trend of model/ensemble guidance in recent days has continued to be toward stronger ridging aloft over the northeastern Pacific and into parts of the mainland/Bering Sea. This ridge will promote a storm track well to the west and north of the mainland while associated fronts may reach into the northern half of the mainland. Guidance has been consistent in suggesting that the leading system Fri-Sat will be much stronger than the second that should cross the Arctic around Sun-Mon. An ongoing uncertainty will be how moisture/energy around the northern side of an upper low over the central Pacific--and perhaps the upper low itself as it weakens/opens up--may interact with larger scale flow and bring moisture into the eastern Aleutians and western mainland. Among guidance available through the 12Z cycle, the ECMWF/UKMET/CMC are noticeably stronger with the upper ridge and show greater westward extent versus the GFS/GEFS mean from early in the forecast period. The multi-day trends toward a stronger ridge seem to provide good support for using the 12Z ECMWF/UKMET/CMC as the starting point of the forecast from late week into the weekend. From late weekend into early next week most 12Z solutions have significantly increased the degree to which the central Pacific upper low opens up, leading to more moisture reaching the eastern Aleutians/Alaska Peninsula as well as some locations farther north. This change is more difficult to gauge for now, as upstream energy dropping into the overall central Pacific trough may play a role in addition to specifics of the upper ridge. At the very least the preference for the ECMWF cluster in principle would keep the shortwave/upper low energy and moisture somewhat farther west than forecast by the GFS. Current preference is for a conservative transition to this idea presented in the 12Z guidance, by way of trending the forecast to about an even weight among the 12Z ECMWF/CMC and 00Z ECMWF/ECMWF mean. ...Weather Highlights/Threats... The initial storm tracking into/across the Arctic late this week may bring an episode of strong winds and terrain-enhanced precipitation to parts of the northwestern mainland but multi-day trends for a stronger upper ridge to the south have continued to trim away the southeastward extent of these effects. Moisture/precipitation flowing from the North Pacific into the Bering Sea may extend into parts of the western/northern mainland along the fronts trailing from the first Siberia-Arctic system and a second weaker system. Depending on evolution aloft over the North Pacific by next Mon-Tue, precipitation may increase/spread slowly eastward over the eastern Aleutians/Alaska Peninsula with some of this activity extending to the north as well. Cold high pressure will support below normal temperatures over the southeastern corner of the mainland into the Panhandle on Fri with some pockets of below normal readings possibly persisting over this area thereafter. Otherwise expect above to well above normal temperatures to prevail across the state with the greatest anomalies most likely to be over northwestern areas. Rausch 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 Hazards: - Heavy snow across portions of mainland Alaska, Thu-Fri, Mar 12-Mar 13. - High winds across portions of mainland Alaska, Thu-Fri, Mar 12-Mar 13. - Much above normal temperatures across portions of northern mainland Alaska, Fri-Mon, Mar 13-Mar 16. - Much above normal temperatures across portions of central mainland Alaska, Sat-Mon, Mar 14-Mar 16. - Much below normal temperatures across portions of the Alaska Panhandle and mainland Alaska, Thu-Fri, Mar 12-Mar 13. 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