Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 657 PM EST Thu Feb 02 2023 Valid 12Z Mon Feb 06 2023 - 12Z Fri Feb 10 2023 ...Overview... The primary focus early in the period will be mean troughing and an embedded upper low near the southwestern coast of the mainland with fairly strong low pressure tracking over or near the Kenai Peninsula as of early next Monday. This system should produce heavy precipitation and strong winds along parts of the southern coast heading into the start of the forecast. With time, the initial upper trough should weaken and possibly give way to upper ridging over the mainland as guidance consensus shows a very strong storm tracking into or near the western Aleutians by Thursday-Friday. In-between there is a tremendous amount of uncertainty from Tuesday onward over the details of North Pacific flow and how much interaction there may be with with northern stream energy over the Bering Sea. These issues aloft lead to a wide array of possibilities for surface evolution and how much moisture ultimately reaches areas from the Aleutians through the Alaska Peninsula/southern coast/Panhandle. Meanwhile expect an upper weakness along or near the northern coast of the mainland with some influence on position from the aforementioned flow uncertainties. ...Model Guidance/Predictability Assessment... Regarding the system forecast to reach the southern coast by early Monday, an average of the 12Z GFS/ECMWF provided the most appealing starting point with a position over the Kenai Peninsula at that time. The GFS helped to average out the ECMWF that strayed a bit east of other solutions (with the new 12Z ECMWF mean between the last two ECMWF runs). Sporadic GFS runs and occasionally another model showed the parent low tracking farther northwest, so that is still a possibility worth monitoring. However there is a signal for a separate low to be near the southwestern coast of the mainland in association with the upper low. Behind this system, guidance is all over the place with respect to how shortwave energy may evolve from initially low-amplitude North Pacific flow and the degree to which Bering Sea energy could interact. During the first half of the week the latest GFS runs and 12Z CMC are strongest with the system initially just south of the Aleutians. Then the GFS begins to show phasing with energy farther north, ultimately leading to a more amplified trough and downstream ridge with additional northward-moving surface waves helping to focus a pronounced moisture feed into the southern coast. In varying ways the 12Z ECMWF/CMC and GEFS/CMCens means show less potential for phasing aloft and keep the strongest surface low pressure to the south of the Alaska Peninsula. The 12Z GEFS/CMCens means share some similar ideas with a track that gets close to the Kenai Peninsula/Kodiak Island by day 8 Friday. The 12Z ECMWF keeps its low well south while the new 12Z ECMWF mean also trends well south of the other two means after the 00Z ECens mean was less defined and eventually farther south. Preference was to depict a moderately defined system south of the Aleutians by Tuesday and then trend toward a compromise among the various non-GFS evolutions to provide some degree of continuity in principle. This scenario allows for some moisture to reach the southern coast and surrounding areas but between the two extremes of the very wet GFS and relatively dry ECMWF. The details within the overall weakness aloft near the northern coast of the mainland are also somewhat uncertain, with ECMWF/CMC runs in particular varying with where an influential upper low could be while the GFS pushes this weakness northward due to its aforementioned differences farther south. The ensemble means provide a reasonable conservative forecast with the axis of this weakness along or a little north of the northern coast. Meanwhile guidance shows much better agreement for the deep storm expected to track into the western Aleutians. Latest model runs suggest the central pressure for this storm could reach into the 940s-950s mb by Thursday-Friday. ECMWF mean runs are quite a bit deeper than the GEFS/CMC means. For now the manual forecast depicts a low 960s mb system by early next Friday with model continuity over the next day or so determining how much deeper of a system appears reasonable. Based on the various forecast considerations, the day 4 forecast started with a 12Z GFS/ECMWF compromise. Then the blend started to phase out the GFS in favor of more GEFS mean, while including some CMC/CMCens and maintaining some ECMWF weight. By day 8 Friday the GFS issues near the mainland became less pronounced, allowing for reintroducing it to the blend in order to get the Aleutians storm a little deeper than the blend would otherwise be. ...Weather/Hazard Highlights... The system near the Kenai Peninsula as of early Monday may produce some lingering enhanced precipitation and brisk to strong winds along the southern coast and Panhandle into the day. Lingering upper troughing/surface low pressure may allow for lighter precipitation to continue along the southeastern coast/Panhandle into Tuesday. Then the forecast confidence decreases considerably the rest of the week from the Aleutians into the southern coast/Panhandle. Current preference is for a system to track just south of the Aleutians and continuing eastward, with a broad enough circulation to bring at least some moisture to areas from the Aleutians through the southern coast and Panhandle. Away from this scenario, possibilities range from a south-to-north storm track that could bring significant totals to parts of the southern coast, to the opposite with relatively dry conditions. With better confidence in principle, expect a deep storm to track into or near the western Aleutians late in the week, spreading precipitation and areas of strong winds across the Aleutians and surrounding waters. Well below normal temperatures will prevail over far northern areas early in the week with readings gradually moderating over the course of the week. Initial upper troughing may keep locations near the western coast of the mainland below normal early-mid week while the Interior/Southcentral/Panhandle should see a mix of above/below normal highs and more above normal lows. Temperature increases toward the end of the week will depending on if/how quickly upper ridging builds over the area. Rausch Hazards: - Heavy precipitation across portions of mainland Alaska, Sun, Feb 5. - High winds across portions of mainland Alaska, Sun, Feb 5. - Much below normal temperatures across portions of mainland Alaska, Sun, Feb 5. 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