Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EST Tue Feb 02 2021 Valid 12Z Sat Feb 06 2021 - 12Z Wed Feb 10 2021 ...Overview and Guidance/Uncertainty Assessment... Most guidance suggests an evolution toward a fairly blocky regime during the period. The majority cluster has an upper low dropping southwestward into the mainland while a varying amount of elongated ridging persists to the southwest, from near the eastern Aleutians into east-central Siberia. The approach/arrival of the upper low will likely promote a significant colder trend, led by a front that pushes southward over most of the mainland during the weekend and start of next week. Shortwaves within the cyclonic mean flow to the southwest of the upper low should hold surface low pressure over or near the Gulf of Alaska for most of the period. Meanwhile flow around the western side of the elongated ridge may bring one or more features northward through the western Aleutians. At the start of the period early Sat there has been a significant degree of spread and/or trending for specifics of low pressure likely to be over the Gulf. 00Z/12Z CMC runs hold the upper dynamics/surface low pressure well westward of other 12Z models and ensemble means, reflective of yesterday's majority cluster. On the other hand the new 12Z ECMWF has strayed even more progressive/sheared than remaining 12Z guidance. Latest means offer the best support for the 12Z GFS/UKMET and 00Z ECMWF in principle, so the early part of the forecast blend emphasizes those solutions with only modest 12Z ECMWF input. Guidance spread and variability thus far keep confidence on the lower side for specifics of the upper low arriving from the northeast. There has been a decent signal over the past couple days for retrogression of height falls anchored by at least an elongated trough if not a closed low, but by day 8 Wed there is a pronounced trend toward holding lower heights over the mainland. The greatest ensemble spread exists to the south and west of the mean low center, highlighting the ongoing uncertainty. The 00Z/12Z ECMWF runs lie in the southwestern extreme of the spread while the 12Z CMC mean keeps the upper low north of the mainland through the period. The operational CMC keeps the center north as well but does eventually dig a trough into the mainland. Overall a solution closest to the 12Z GFS and 12Z GEFS/00Z ECMWF mean cluster seems to provide the best intermediate way to reflect latest trends. Thus the blend during the latter half of the period emphasizes those solutions with only minimal ECMWF inclusion. ...Weather/Hazards Highlights... Persistent low pressure over the Gulf of Alaska will tend to focus periods of precipitation over the southeastern coast and Panhandle through the period. A leading wave arriving by the start of the weekend should provide the initial push of moisture with moderate totals expected. After the weekend there is increasing uncertainty over precipitation intensity over this area, depending on specifics of the upper low/trough that may move into the mainland. Current guidance preferences would yield light-moderate activity most of the time but an upper flow orientation that could bring greater moisture into the region is a lower-probability but possible scenario. One or more features lifting up the western side of upper ridging may support episodes of precipitation/brisk winds over portions of the Aleutians and southwestern half of the Bering Sea. The weekend will start with above normal temperatures over southern/western areas and below normal readings to the north/east. Then a colder trend from north to south will likely yield below to well below normal readings over much of the state during the first half of next week. 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: - Much below normal temperatures across portions of mainland Alaska, Mon-Tue, Feb 8-Feb 9. 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