Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EST Mon Feb 03 2020 Valid 12Z Fri Feb 07 2020 - 12Z Tue Feb 11 2020 ...Overview... During the course of the period guidance shows a mean ridge building over the northeastern Pacific into the mainland of Alaska and northwestern Canada, with varying degrees of troughing to the west. One or more shortwaves will likely pass through/around the mean ridge to provide a brief interruption in the trend toward higher heights within the overall ridge. As has been the case in recent days, models and ensembles display a fair amount of spread for multiple individual features in spite of the better agreement for large scale evolution. Among today's solutions the best guidance clustering varies depending on the feature. This required using a multi-model blend (12Z/00Z ECMWF and 12Z GFS/UKMET/CMC) to emphasize the most common specifics during the first half of the period, followed by a trend to a model/ensemble mean blend (the means represented by 12Z GEFS/00Z ECMWF mean) as details become increasingly uncertain. ...Guidance Evaluation... The forecast of the upper low and surrounding trough expected to be near the northwest corner of the mainland continues to be problematic with a multitude of ideas for precise evolution/position depending on the day. The full range of guidance ranges between keeping the upper low/trough over or very close to the northwestern mainland into day 6 Sun, and retrogression or shearing/reforming of the upper low into Siberia. Then the question becomes how this feature ejects eastward around the building ridge downstream. At the very least the latest GFS runs may be somewhat too deep/amplified early next week. General preference to trend the forecast somewhat more toward the means by the latter part of the period across the full domain ultimately leads to reflecting the retrogression scenario, but with low confidence. Behavior of guidance thus far is suggesting it will take into the short range time frame for this aspect of the forecast to be resolved. The preferred forecast of North Pacific into Bering Sea/western mainland low pressure Fri-Sun stays close to continuity, with the 00Z ECMWF and 12Z CMC/UKMET/GEFS mean providing the majority cluster. This would have a triple point wave tracking from the North Pacific into the Bering, and then across the western mainland. During Fri-Sat the GFS differs from most other guidance in rapidly weakening the upper low associated with the western parent low and forming a deep upper low to the east--but still behind the leading triple point system depicted in other guidance including the 12Z GEFS mean. Track/evolution of this system will depend on the very uncertain specifics of the upper low/trough initially near the northwestern mainland. During the latter half of the period the continued northward/northeastward progress of western mainland low pressure should bring a cold front across a large portion of the mainland. Meanwhile North Pacific/Aleutians shortwave energy may briefly generate a surface wave over or near the Gulf of Alaska around day 7 Mon. Current model/ensemble mean consensus indicates that such a wave should be somewhat weaker and northward/faster than the past couple ECMWF runs--though the 12Z run at least trended weaker and faster than the 00Z run. Farther west there has been a decent signal for organized low pressure from the western Pacific into western Bering Sea during the latter half of the period. Thus far the ensemble means have provided the most consistent solutions. GFS runs through the 00Z cycle had been the most consistent operational guidance for general strength/track/timing but 06Z and 12Z runs have strayed in various ways. On the other hand the last two ECMWF runs have come into better agreement with the means. The 12Z CMC is near the favored cluster into early Mon before becoming a fast northeast extreme. ...Weather Highlights... A weakening system near the southwest corner of the mainland as of early Sat should produce light-moderate precipitation along the southern coast late in the week. The stronger trailing system forecast to track into the Bering Sea/western mainland should bring an episode of brisk to strong winds, as well as enhanced precipitation from the eastern Aleutians/Peninsula into parts of the mainland. The moisture should extend eastward across the southern coast as well. This system will support a northward surge of warmer air and lead to well above normal temperatures over much of the mainland after northern/western areas see well below normal readings Fri-Sat. Passage of a trailing cold front may provide a modest cooling trend late weekend and early next week but with anomalies staying on the warm side of normal. Low pressure expected to track from the western Pacific into the western Bering Sea around Sun-Tue may spread a broad area of fairly strong winds across the Aleutians and Bering Sea. 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: - High winds across portions of mainland Alaska and the Aleutians, Fri-Mon, Feb 7-Feb 10. - Much below normal temperatures across portions of mainland Alaska, Thu-Sat, Feb 6-Feb 8. 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