Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 659 PM EST Tue Feb 27 2024 Valid 12Z Sat Mar 02 2024 - 12Z Wed Mar 06 2024 ...Very cold temperatures over a majority of the state late this week into the weekend... ...Overview... Model guidance indicates an amplified upper pattern across Alaska through the end of the week, consisting of a narrow ridge atop the Alaska Peninsula through the eastern Bering Sea and the western Mainland on Saturday with troughing on either side. Northerly mean flow, lingering troughing in the eastern Interior, and cold surface high pressure will promote very cold temperatures over much of the state late week. Into early next week, the fate of the ridge becomes the main question that has shown ample spread in the models. There seems to be a tentative consensus building that ridging will persist rather than be quickly eroded by energies coming in from the northeast and west. This provides more quickly moderating temperatures especially to western and central parts of the state while reducing precipitation chances for Southeast Alaska early next week. ...Guidance Evaluation and Preferences... Model guidance is in good agreement for the start of the model diagnostics period Saturday in showing troughing across the Aleutians pushing a frontal system eastward toward the Alaska Peninsula, while narrow upper ridging is in place to the east with another trough poking in from northwestern Canada downstream of that. Cold surface high pressure is also agreeable. But by Sunday-Monday, models have struggled tremendously to reach a consensus even on the synoptic scale. After a trend with 12Z models on 2/26 to indicate more upper troughing across the Interior as energy especially emerging from the northeast eroded the ridge, today's models are trending toward more ridging remaining into early next week, though not uniformly. The main holdout into the 12Z cycle that still showed troughing into Day 6/Monday was the 12Z GEFS mean, as the 12Z GFS and CMC did switch to a ridge pattern after earlier runs indicated a trough. ECMWF runs from 12Z and 00Z showed ridging and so did the 00Z ECMWF mean that was available at forecast production time (after the 12Z EC mean from 2/26 was troughy). So with the bulk of guidance now showing a ridge persisting, today's forecast leaned in this direction. The incoming 18Z GEFS mean has started to trend toward more of a ridge through Monday as well, which may be a good sign, though it is not as strong as other models/means. By Tuesday, the ridge does seem to start getting shunted east and eroding as stronger Bering Sea troughing comes in from the west. A brief bout of ridging may be possible over the Aleutians/Alaska Peninsula Tuesday-Wednesday while additional energy emerges from the Bering. Surface lows and frontal systems are likely for the Bering/Aleutians but certainly the details will evolve with time. Given these considerations, the WPC forecast used a model blend favoring the 12Z ECMWF/CMC/GFS and 00Z EC mean, leading to upper ridging remaining more amplified across the state through early next week. Increased the proportion of the EC mean to about half by the end of the period. ...Weather/Hazards Highlights... As highlighted on the Days 3-7 Hazards Chart, the pattern late this week will support a broad area of hazardous cold temperatures across a majority of the mainland to the south of the Brooks Range. This will be from a combination of actual air temperatures (possibly approaching -40 degrees over the typically coldest eastern Interior locations) or wind chills farther south and west. Much below normal temperatures are also likely for Southeast Alaska. Temperatures should gradually moderate from west to east through the weekend into early-mid next week, especially considering the trend toward a sustained upper ridge. Northwestern areas of the state look to reach above normal temperatures this weekend and last into early-mid next week. A Bering Sea frontal system and trailing wave will spread organized precipitation across the Aleutians/Bering Sea and into/near the Alaska Peninsula into Saturday. Some moisture could stream farther north and affect western parts of the state with mostly light snow. Persistent mean southwesterly flow should promote precipitation chances remaining across the Alaska Peninsula, Kodiak Island, and the southwestern Mainland into early next week. Some light snows may impact much of the Interior by around Tuesday. Meanwhile, the trend toward a stronger ridge across the Interior also leads to significantly lowered precipitation chances for Southeast Alaska given the dry mean northerly flow. So if this forecast holds, only light precipitation is likely there with perhaps a wetter shift into midweek. Winds and precipitation may be enhanced for the Aleutians again next week when frontal systems pass through. There could also be concerns for localized gap/outflow winds farther east across the southern coast of the state, but there is not any good consensus for strong winds at this point. Tate 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