Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 648 PM EST Thu Jan 18 2024 Valid 12Z Mon Jan 22 2024 - 12Z Fri Jan 26 2024 ...Overview... Expect a narrow/elongated upper trough over the mainland as of Monday to shear out quickly ahead of approaching Siberia/Arctic trough energy that will likely settle over the mainland and possibly extend into the Gulf of Alaska for the latter half of the week. During that time a Bering Sea upper ridge should build, but not to such a strength as the one currently over the region. Meanwhile, a broad area containing one or more upper/surface lows should prevail south of the Alaska Peninsula/eastern Aleutians early in the week followed by some uncertainty over whether some of this low pressure or other developing systems reach the northeastern Pacific/Gulf versus low pressure developing in place over the Gulf in response to the mainland upper trough. The overall forecast pattern 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. ...Guidance Evaluation/Preferences... Model spread and run-to-run variability continue to keep confidence low for exact details within the overall area of low pressure south of the Alaska Peninsula/eastern Aleutians during the first half of the week. Overall the 12Z ECMWF appears closest to the ensemble means for surface low emphasis. The CMC/UKMET leans a little farther northwestward but not by an extreme degree, so a 12Z model composite employing 40 percent ECMWF and the remainder split among the GFS/UKMET/CMC provide a reasonable starting point early in the period. With Siberia/Arctic upper troughing arriving into the mainland, guidance spread and variability between runs also temper confidence in any particular solution and favor an intermediate approach. The GFS/ECMWF/CMC have all waffled between runs. The 12Z ECMWF become more amplified than the 00Z run while the 12Z CMC backed off from the 00Z run's amplified trough (with some similarities between the 12Z ECMWF and 00Z CMC), and the 12Z/18Z GFS runs becoming flatter than prior runs or other guidance. Even the ensemble means vary, with latest GEFS/ECens runs not as amplified as some versions 24-48 hours ago and the CMCens more amplified than the other two means. These differences suggest a lot of uncertainty regarding the extent to which the trough may interact with initial North Pacific upper energy/surface low pressure. At least a moderate amount of upper troughing would support some surface low pressure over the Gulf by late in the week--regardless of whether it tracks there or develops in place. Behind the upper trough, there is good agreement with an upper ridge building into the Bering Sea. Latest GEFS/ECens means support the operational model scenario of a closed high by next Friday (CMCens weaker and more open). However the 12Z/18Z GFS runs become a northern extreme with the upper high position. After the 12Z model blend employed early in the period, guidance differences/shifting trends led to splitting ECMWF input between the 12Z and 00Z runs, replacing the 12Z GFS with the 06Z run, and incorporating 30-40 percent total weight of the 12Z GEFS/00Z ECens means to yield the desired intermediate solution. ...Weather/Hazards Highlights... Interior and southwestern areas will likely see well below normal temperatures for most days next week. Some overnight lows should drop into the -20s and -30s, with even localized -40s possible in favored valleys of the Yukon Flats. The North Slope and Southcentral/Panhandle will generally see near to above normal temperatures. Pacific moisture will produce moderate to locally heavy snow from the Kenai Peninsula to the St. Elias Mountains during the first half of the week. Expect this activity to trend lighter from west to east later in the week. Coastal rain and mountain snow should be more persistent over the Panhandle during next week. The Alaska Peninsula/eastern Aleutians could see some precipitation early in the week followed by a drier trend. Away from the southern coast, most of the state will be relatively dry with at most a few areas of light/scattered snow. Anticipate separate early and late week periods featuring a strong pressure gradient between northern tier high pressure and Pacific/Gulf low pressure. This gradient may produce some strong northerly winds from the eastern Aleutians through the Alaska Peninsula to around Cook Inlet/Kenai Peninsula. 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