Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 652 PM EST Sun Jan 01 2023 Valid 12Z Thu Jan 05 2023 - 12Z Mon Jan 09 2023 ...Overview and Guidance/Predictability Assessment... Most of today's guidance continues to show similar ideas in the large scale but again various embedded detail issues that have much lower predictability/confidence. The most dominant features will be upper ridging over western Canada and a mean low that will most likely progress from the northwestern Pacific through the Aleutians and then continuing eastward near 50N latitude. The best clustering of guidance suggests better potential for the Canada ridge to extend farther into the mainland by the weekend and early next week. Within this evolution, one or more systems may track north/northwest over the northeastern Pacific (with some precipitation/wind effects for the Panhandle and southern coast) while multiple lows/fronts may affect the Aleutians and adjacent waters. There is also a question of flow details over the mainland, with one or more shortwaves lifting northward between the Aleutians low and Canada ridge. The best defined northeastern Pacific system of note should reach near or west of Haida Gwaii by early day 5 Friday. With typical spread, there has been a decent signal for this system up to about the early Friday time frame, with the ensemble means starting to hold onto a better signature of this system beyond Thursday than they have in previous days. However after early Friday there is still a lot of spread regarding the strength of the system and its track, or even whether a trailing system could interact/take precedence. A 12Z operational model blend of the ECMWF, UKMET, and GFS/CMC in order from more to less weight through day 5 Friday and then followed by splitting the ECMWF/GFS input with their prior runs into early day 6 Saturday to account for some other issues as well, yielded fairly modest adjustments to continuity. Other trailing waves have minimal confidence and are not depicted in the favored blend. Over the mainland, guidance becomes quite varied with smaller details aloft mid-late period. The past couple 00Z ECMWF runs have been using some of the northward-drifting shortwave energy to form a closed low while the 12Z CMC/GFS do the same over the far northwest by day 8 Monday (with the CMC holding more troughing over the rest of the western mainland as well). 12Z ECMWF runs have been adjusting to faster/more open energy and 00/06/18Z GFS runs lean to more ridging as well. The GEFS/ECMWF means have been fairly consistent in showing the Canada ridge extending into the mainland, so preference favors that scenario. Along the northern coast the operational guidance has backed off from the upper weakness that it was developing toward the end of the week in yesterday's runs. This latest trend is a nod to the ensemble means which have been fairly modest with such a feature in recent days. Models continue to show an assortment of seemingly random individual surface lows associated with the mean upper low tracking toward/through the Aleutians (or extending north into the Bering Sea/south over the Pacific) during the latter half of the week into the weekend. The favored model blend during the first 2-3 days of the period does happen to yield a primary western Aleutians low (possibly representing some periodic reinforcement along the way) that has decent ensemble mean support. A more notable question mark arises around Sunday with sporadic operational model runs over the past couple days holding onto an upper low/surface system over the Aleutians/Bering Sea (as in the 12Z ECMWF and 12Z/18Z GFS) while most ensemble mean runs have been showing a greater shift of low pressure emphasis farther eastward by that time. For now prefer a solution more like the ensemble mean continuity but with a surface trough extending northwest to where a lingering low could be. This large scale system is most likely to continue east along 50N into day 8 Monday. Consensus shows another large scale system emerging over the western Pacific late in the period. Recent trends have been farther south with the track, reducing any northern periphery effects on the Aleutians. The 12Z/18Z GFS runs stray to the fast side, ultimately pushing the leading system ahead of consensus as well. The 06Z GFS generally matched up better with ECMWF runs and the means across the Pacific late in the period. ...Weather/Hazards Highlights... The forecast pattern should continue the potential for periods of precipitation along the Panhandle and southern coast. The best defined system of interest may track near or west of Haida Gwaii by early Friday and farther north/northwest thereafter, possibly spreading moisture over the Panhandle with some wind enhancement as well depending on how closely the system tracks. Confidence then decreases with respect to how much of this system's moisture may reach the southern coast. One or more other waves could brush the region but again with low confidence for what focused precipitation they may produce. Most of the remainder of the mainland will likely experience dry conditions except for perhaps very light/scattered snow with any passing upper shortwaves. The Aleutians will see an unsettled pattern during the latter half of the week into the weekend as multiple waves/frontal systems bringing varied wind and precipitation (mostly rain) focus. Confidence remains below average for exact details. Low pressure emphasis may shift farther to the east-southeast by next Sunday or Monday. This could increase easterly low level flow over the eastern Aleutians/Alaska Peninsula and vicinity at that time. Much of the state should see above normal temperatures through the end of the week, with greater anomalies for lows. As readings trend gradually cooler with time, some areas of slightly below normal highs may develop over parts of the central and southern-southwestern part of the mainland. 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