Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Sun Feb 05 2023 Valid 12Z Thu Feb 09 2023 - 12Z Mon Feb 13 2023 ...Deep low pressure likely to bring strong winds to the Aleutians and surrounding waters Thursday-Friday... ...Overview... Guidance is slowly trying to converge for specifics of shortwave energy and associated low pressure that should bring an episode of enhanced precipitation/wind to the Alaska Panhandle. However today's models have suddenly diverged significantly regarding what had been a fairly agreeable and consistent signal for strong low pressure tracking into the Aleutians and Bering Sea. Current preference holds onto this strong low scenario pending more reliable trends, while the new array of possibilities for parent low(s) and subsequent waves would at least support the general idea of meaningful precipitation progressing from the Aleutians across the southern coast of the mainland and into the Panhandle. Another system emerging from the western Pacific may increase winds/precipitation over the Aleutians by day 8 next Monday. Farther north, the ensemble means and model average keep an upper weakness along the northern coast of the mainland but with uncertain specifics. ...Model Guidance/Predictability Assessment... The forecast over the northeastern Pacific/Alaska Panhandle and vicinity for late this week has become more agreeable and stable over the past couple days but some differences remain. The 12Z and 00Z ECMWF runs and 12Z CMC (with support of the ECens/CMCens means) best represent the guidance average and recent consensus for the track of low pressure and extent of associated moisture. Recent GFS runs and the 12Z GEFS have been somewhat south, though the 12Z/18Z runs represent a northward nudge versus 06Z/00Z versions, while the UKMET has been on the strong/northwest side of the spread. Latest GFS and UKMET runs in particular have thrown the North Pacific through Bering Sea forecast into chaos, significantly changing exactly how Pacific shortwave energy and associated low pressure systems evolve. The 18Z GFS and 12Z UKMET are sufficiently flat and progressive with the overall flow that their systems are now weaker with a track south of the Aleutians. The 12Z GFS was a partial trend in this direction, initially splitting the dynamics/surface reflection into two waves with the second one ultimately taking over and tracking southeast of established consensus/continuity (but still getting as far north as the southeastern Bering Sea). The 12Z GEFS mean was partway between the 12Z GFS and the 06Z GFS plus ECMWF/ECens that have most closely represented continuity from Thursday into Saturday. The 12Z CMCens is closer to the ECMWF cluster at least through late week. After early Saturday, the 12Z ECMWF/ECens mean have both trended faster with the primary low than the 00Z run (though whether the Bering low ultimately drops south of the Alaska Peninsula per the 12Z ECMWF remains to be seen). With the 12Z ECens mean not yet available to gain additional confidence in any trends at the time of forecast preparation, today's forecast emphasized a blend among the 00Z/12Z ECMWF and 06Z GFS to maintain the best continuity possible in light of the guidance spread and variability. General signals continue for separate waves (initially embedded along the parent storm's front, or otherwise) to reach areas from the eastern Aleutians into southeastern Bering and eastward along the southern coast. Initial preferences for leaning more toward ECMWF runs led to some reflection of a southeastern Bering wave in the manual forecast around early Saturday but in toned-down fashion given the lack of confidence in specifics. In one way or another, there is decent persistence in the ensemble means and some models for another wave reaching near the Kenai Peninsula/Kodiak Island by early Sunday with low pressure or at least a surface trough persisting along the southern coast/Panhandle into Monday. Regarding the next storm emerging from the western Pacific, operational models over the past couple days have been consistent in depicting a fairly strong system but with a lot of latitudinal spread. The 12Z/18Z GFS runs are farthest south with minimal influence on the Aleutians. Currently the latest ECMWF runs have the best track agreement from the ensemble means. Interestingly the GEFS/ECens means had been trending weaker over the past couple days before the 12Z ECens became somewhat deeper. The 12Z GEFS mean is quite weak while the CMCens mean is strongest among the means. Preferences over the northeastern Pacific early in the period and to maintain reasonable continuity for the Aleutians/Bering Sea storm led to starting with a blend of the 12Z/00Z ECMWF for days 4-5 Thursday-Friday, followed by adding some 06Z GFS in with those ECMWF runs from late day 5 into day 7 Sunday. Detail uncertainties within the favored scenario and wanting the strongest means to include for the emerging western Pacific system led to incorporating 40 percent total 12Z CMCens/00Z ECens guidance with the operational runs by day 8 Monday. ...Weather/Hazard Highlights... Continue to expect low pressure lifting up into the northeastern Pacific/Gulf during Thursday into early Friday to bring a period of enhanced precipitation to the Panhandle, with some fairly strong southerly winds as well. The best potential for highest totals still exists over the southern half to two-thirds of the Panhandle while there is lingering uncertainty regarding the northward extent and amounts over the northern Panhandle (and more unlikely over the far southeast corner of the mainland. Previous confidence for the potential deep storm forecast to track into the western Aleutians and then the Bering Sea late week into the weekend has decreased compared to previous days, with guidance diverging for important specifics of surface low track and strength. Following a solution fairly close to continuity while evaluating the reliability of new trends, still expect a period of strong winds over the Aleutians and surrounding waters, especially around Thursday-Friday, with precipitation spreading across the region as well. A leading front and one or more waves should spread locally moderate to heavy precipitation across the southwestern mainland/Alaska Peninsula by Friday and continuing eastward along the southern coast and into the Panhandle thereafter, with the Panhandle likely to see multiple days of precipitation. Expect much lighter and less organized snowfall farther north across the mainland. Winds and precipitation may increase over the Aleutians once again by next Monday with the approach of another Pacific storm. Below normal temperatures will tend to prevail over the North Slope and western parts of the mainland during the latter part of the week. A persistent weakness aloft near the northern coast of the mainland, with recent guidance trends toward lower heights aloft suggesting that cold readings over the North Slope may persist a little longer than in previous forecasts. Elsewhere temperatures should trend notably warmer to mostly above normal levels by Sunday and Monday. A cooling trend may begin to move in from the west early next week. 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