Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 634 PM EST Tue Feb 18 2025 Valid 12Z Sat Feb 22 2025 - 12Z Wed Feb 26 2025 ...Overview... Latest guidance shows a fairly persistent mean ridge aloft extending over the mainland from the Panhandle and western Canada, most likely weakening a bit during the weekend but rebuilding by Monday-Wednesday. Meanwhile shortwave energy over the North Pacific will support multiple surface lows reaching into or near the Gulf of Alaska, most likely providing the best precipitation focus over the Panhandle and to some degree the Southcentral coast. These lows combined with Arctic high pressure will keep most of the mainland within the surface gradient. Parts of the North Slope may see brisk winds as a result. Another area of low pressure should wobble over the Bering Sea before eventually weakening, and finally the northern periphery of a much deeper storm reaching the central Pacific by next Wednesday may affect the Aleutians. ...Guidance Evaluation and Preferences... Detail predictability appears below average for the overall area of low pressure initially forecast to track over the northeastern Pacific and possibly reach into the Gulf of Alaska during the weekend into early next week. The upper dynamics are rather diffuse and different solutions vary with respect to which of multiple lows may become the more dominant one, or perhaps merge into a single low. A relative majority of operational guidance and machine learning (ML) models show a somewhat faster/eastward evolution compared to yesterday's continuity before curling back toward Kodiak Island, though the 12Z ECMWF/UKMET are still somewhat on the slower side. A composite of the past two ECMWF runs, the 06Z GFS, and some ensemble mean input (12Z GEFS/00Z ECens) reflects the prevailing themes of latest guidance while maintaining a coherent system. Most guidance shows a better defined system tracking into the northeastern Pacific/southern Gulf of Alaska by next Wednesday. The overwhelming majority of dynamical and ML guidance suggests that the 12Z/18Z GFS and to some degree the 12Z GEFS mean may be too far west for the low track and associated wind/precipitation effects. The 06Z GFS compared better to the dominant guidance cluster. Dynamical models and means show better than average agreement regarding the strong low pressure forecast to reach the central Pacific by next Wednesday. A number of operational model runs have been showing a depth in the 940s/950s mb and even most of the ML models are within a few on either side of 960 mb. Latest ensemble means are generally in the low-mid 970s. The ML model and ensemble mean values are both pretty good signals for a deep storm by typical Day 8 standards. A multi-model blend looks like a good starting point, accounting for some of the typical uncertainty at that time frame but yielding a deeper solution than the means. This system will be worth monitoring in coming days as it may have some influence on the Aleutians, and beyond the current extended period potentially the southern coast. The detail uncertainty over the northeastern Pacific early-mid period led to a Saturday-Monday blend consisting of a split of the 12Z/00Z ECMWF runs, the 06Z GFS, and 30 percent total of the 12Z GEFS/00Z ECens means. With better defined systems over the northeastern Pacific and central Pacific by Tuesday-Wednesday, the forecast replaced the ensemble mean component with the 12Z CMC. This provided reasonable definition along the majority track for the system likely to track into the Gulf next Wednesday while reflecting the aforementioned favored starting point for the central Pacific storm. The forecast blend also helped center the forecast of Bering Sea low pressure which also exhibited some scatter for specifics but was more stable from a model/mean average perspective. ...Weather/Hazards Highlights... Expect the Panhandle to see the highest precipitation totals during the period, in association with one or more surface waves forecast to track into the Gulf. Some of this activity should extend back into the Kenai Peninsula and Prince William Sound area. Most precipitation will likely be in the form of rain over the southern Panhandle and along the coast while the higher elevations see snow. A better defined system that may track into the Gulf by next Wednesday could produce a somewhat more pronounced moisture focus. Note that there is a small minority among guidance for this latter system that would bring the low track and moisture shield farther west. Some localized areas could see several inches or more of liquid over the five-day period but totals probably will not reach hazardous criteria on a daily basis. Precipitation will be lighter away from the coast with the only potential focus of note being a weak front through the southern interior portions of the state. The gradient between persistent high pressure over the Arctic and the surface lows over the northeastern Pacific/Gulf will produce some brisk winds, in particular across parts of the North Slope. Forecast wind speeds are currently not high enough to merit depiction on the Days 3-7 Hazards Outlook but will be worth monitoring in coming model cycles. Finally, the northern periphery of the deep storm forecast to reach the central Pacific by next Wednesday may bring brisk winds and some precipitation to the Aleutians. Effects will be sensitive to the exact latitude of the storm. The mean upper ridge across most of the state will keep temperatures well above normal through the period over most areas, with some locations across especially southwestern and southern Alaska possibly seeing daytime highs up to 20-30F above normal. Parts of the North Slope could see one or more days with temperatures closer to normal. Rausch 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