Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EST Fri Jan 19 2024 Valid 12Z Tue Jan 23 2024 - 12Z Sat Jan 27 2024 ...Overview... The majority cluster of guidance continues to show Arctic/Siberia shortwave energy forming an upper trough over the mainland by mid-late week, but with uncertainty in the specifics. Meanwhile an upper ridge should build over the Bering Sea by late week and lead to additional amplification of mainland troughing into next weekend. One or more areas of surface low pressure and supporting dynamics south of the Aleutians/western Alaska Peninsula may consolidate over the mid-latitude Pacific and track into the northeastern Pacific by the end of next week. A leading system could brush the Panhandle around Wednesday-Thursday. The forecast pattern evolution will confine most precipitation to the southern coast and especially the Panhandle, while keeping temperatures over the interior and southwestern parts of the state well below normal. Expect a tightening pressure gradient to strengthen winds across southern tier areas late in the week. ...Guidance Evaluation/Preferences... There is still a fair amount of spread for details of the upper trough expected to settle over the mainland during mid-late week. While some individual model runs show flatter flow at some valid times, at least what had been the amplified side of the spread (extending the upper trough well into the Gulf of Alaska) has retreated to a more moderate depiction. The 00Z/12Z ECMWF runs and the ensemble means represent the favored intermediate scenario which is close to continuity, with latest GFS runs and 12Z CMC also in the proverbial ballpark for a while anyway. Farther west, significant differences develop with the evolution of the Bering Sea upper ridge. 12Z/18Z GFS runs become more east-west elongated than most other guidance (06Z run more comparable to consensus), and the 12Z CMC strays well westward. The 12Z GEFS mean is weaker than most other solutions. Even within the favored cluster of the ECMWF runs, 06Z GFS, and CMCens/ECens means, there are meaningful longitude differences for the ridge--and deepening mainland upper trough by Saturday--with the 12Z ECMWF/ECens adjusting somewhat westward of their 00Z counterparts. This spread is fairly typical for that far out in time, so a blend of those solutions would provide a reasonable starting point at this time. Over the Pacific/Gulf of Alaska, consensus shows a compact wave in or near the Gulf of Alaska on Tuesday and then becoming ill-defined. A deepening wave well to the south should lift northeastward and possibly brush the Panhandle around Wednesday-Thursday. By early Thursday the operational model runs generally favor slower northward progression than the ensemble means, with the latter possibly combining this system with Gulf low pressure expected to form in response to the mainland upper trough. Guidance is still all over the place with upper/surface low placement south of the Aleutians/Alaska Peninsula early in the period (though notably westward in the GFS/GEFS), affecting the gradient over those land areas. There is a general theme in the models/ensembles for this and mid-latitude Pacific low pressure to consolidate and lift northeastward late in the week. The track and timing of low pressure, whether a deep system as seen in the 12Z ECMWF or perhaps a wave breaking off from the leading front, will be very sensitive to the amplitude and longitude of the amplifying mainland trough as of next Saturday. Prefer a compromise depth for this day 8 low pressure by way of a model/mean blend, which happened to be what the new 12Z ECens mean trended toward. Forecast considerations during the first half of the period favored a starting blend consisting of 45 percent 12Z ECMWF, 35 percent total 06Z/12Z GFS, and 20 percent CMC. Later in the period the guidance differences and favored clustering led to transitioning the blend to 25-40 percent total ensemble mean input (12Z CMCens/00Z ECens) with operational guidance including the 06Z GFS and a split of 00Z/12Z ECMWF runs. ...Weather/Hazards Highlights... Interior and southwestern areas will likely see well below normal temperatures for most days next week. Overnight lows should drop into the -20s and -30s, with even some -40s and possibly -50F or so possible in favored valleys of the Yukon Flats. The North Slope and Southcentral/Panhandle will see more moderate temperatures, including some above normal readings. However the amplifying upper trough over the mainland late in the week will likely push below normal temperatures farther southward over Southcentral and eventually into the far northern Panhandle Thursday onward. Moderate precipitation along the southeastern coast/Panhandle should trend lighter at least briefly into Wednesday. Then with uncertain specifics thus far, a system lifting into the northeastern Pacific may bring some moisture into the Panhandle later Wednesday-Thursday. The potential for deeper low pressure to reach the northeastern Pacific/Gulf of Alaska by next Saturday would bring an episode enhanced precipitation at least to the Panhandle, with westward extent depending on the exact alignment of upper troughing expected to deepen over the mainland. Remaining portions of the state will be relatively dry with at most a few areas of light/scattered snow. From Thursday onward, the combination of surface high pressure becoming established over the north-central mainland and low pressure over and south of the Gulf should strengthen the pressure gradient over the southern tier and produce areas of strong northerly winds from the eastern Aleutians through the Alaska Peninsula to around Cook Inlet/Kenai Peninsula, with the latter region currently seeing the best potential for winds to reach hazardous thresholds. 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