Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 654 PM EST Tue Jan 02 2024 Valid 12Z Sat Jan 06 2024 - 12Z Wed Jan 10 2024 ...Stormy conditions for the Aleutians and western Alaska into the weekend... ...Overview... Latest guidance generally suggests a continuation of the short-term pattern of strong low pressure systems tracking from the North Pacific into the Aleutians and Bering Sea. This track will be upstream from fairly persistent Arctic ridging aloft while an eastern Pacific mean ridge should let a couple shortwaves pass through the northeastern Pacific with associated waves/frontal systems. A leading Aleutians/Bering Sea storm will produce a broad area of strong winds, including parts of the mainland, during the weekend while details are more uncertain for a potential second system by next Tuesday-Wednesday. This pattern will likely produce highest totals of precipitation from the Alaska Peninsula to the Kenai Peninsula. ...Guidance Evaluation/Preferences... Models/ensembles appear to display typical spread for the track/timing/depth of the strong storm reaching the Aleutians and Bering Sea during the weekend. Model consensus shows the lowest central pressure around Sunday, between the upper 940s and 950s mb while the ensemble means are expectedly weaker but still in the upper 950s mb. The past couple ECMWF runs are closest to the middle of the spread, between the slightly weaker/northward CMC and southward GFS. There is reasonable agreement that the storm's leading front should be weakening as it reaches the Gulf of Alaska and offshore the Panhandle by early Monday. However due to shortwave evolution sensitivity, guidance has been more diverse and erratic with a small-scale North Pacific wave which may reach near the Alaska Peninsula by Monday. ECMWF runs have also been more stable with this feature, while the CMC strays north. Among latest GFS runs, the 12Z version was closest to the ECMWF's idea while earlier runs were faster/southward. There is also a split in the guidance as to whether the southern part of the shortwave could close off a low and develop a stronger storm (but with a track south of the Panhandle). Toward the end of the period next Tuesday-Wednesday there is a decent signal for upper ridging to rebuild into the northeastern Pacific and portions of the mainland, but with a fair amount of spread for details of low pressure to the west. GEFS/ECens mean continuity has been in favor of another system tracking through the Aleutians and into the Bering Sea (with latest GFS/CMC runs falling into this cluster). A couple ECMWF runs were suppressed and progressive with low pressure, a scenario not reflected in other guidance. The 12Z ECMWF has adjusted significantly to a slow storm that stays south of the Aleutians through Wednesday, but the 12Z CMCens and ECens (latter not available as of forecast preparation) are also hinting at slower northward progression than established ensemble mean continuity. Preference for now maintains more northward progression into Wednesday but acknowledging the emerging potential for a slower trend. Guidance comparisons/preferences led to starting today's forecast with a 12Z operational model composite (40 percent ECMWF and the rest split evenly among the GFS/UKMET/CMC) for about the first half of the period and then quickly adjusting toward 40 percent ensemble means and lingering input from the GFS/ECMWF/UKMET. This approach reflected the consensus/intermediate solution where desired while downplaying the less confident aspects of a particular model for some features. ...Weather/Hazards Highlights... Before the start of the period, expect high winds across the Arctic Coast/North Slope region to persist into Friday and lead to periods of ground blizzard conditions. Then during the weekend the deep storm tracking northward through the Aleutians and Bering Sea will spread a broad area of high winds across those areas as well as portions of the mainland. Strongest winds over the mainland should be over parts of the Seward Peninsula and Lower Yukon/Lower Kuskokwim regions, with blizzard conditions possible there as well. The combination of the storm's leading front and a potential trailing wave/front will spread precipitation across and east from the Aleutians, with the most pronounced focus likely to be along the Alaska Peninsula and Kenai Peninsula during Saturday-Sunday. Meaningful totals may also be possible a little farther inland over the far southwestern mainland. What moisture reaches the southeast coast/Panhandle will produce much lighter precipitation, while fairly dry conditions should prevail over the Interior and North Slope. By next Tuesday-Wednesday another storm system may bring precipitation and brisk to strong winds to at least the Aleutians if not the Bering Sea and far western mainland as well. Monitor forecasts as details for this latter system become better resolved. Most of the state will see above to well above normal temperatures through the period, with highest anomalies likely over northern and western parts of the mainland. The primary exception will be over the eastern Interior, where negative anomalies should moderate after the weekend, and over the central-southern Panhandle with moderately below normal temperatures. 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