Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 756 PM EDT Thu Oct 24 2024 Valid 12Z Mon Oct 28 2024 - 12Z Fri Nov 01 2024 ...Active pattern with episodes of heavy precipitation and high winds likely across southern coastal Alaska next week... ...Overview... The forecast period spanning the next work week will feature at least a couple vigorous systems that will bring areas of significant precipitation and strong winds to portions of the southern coast/Panhandle and nearby areas, with strong winds also possible back into the Aleutians. A leading Pacific storm will deepen as it track into the Gulf of Alaska early-mid week, enhanced by dynamics initially supporting a northern Bering Sea system that should lose definition after reaching the western coast. At the same time, expect a deeper storm to reach the western Aleutians/Bering Sea with some continued eastward progression into late week. A trailing Pacific storm may come into the picture by next Friday with uncertain influence on the Aleutians. The mainland should see a progression of upper features, with an early Monday ridge followed by a trough and then some degree of ridging. ...Guidance Evaluation/Preferences... Dynamical models and ensemble means now show good clustering and continuity for the system over the northern Bering Sea as of early Monday. The only noticeable difference when comparing the machine learning (ML) guidance is that the ML model average is slightly faster than the dynamical cluster, though well within the typical error range for a days 4-5 forecast. Regarding the Pacific system tracking into the Gulf by Tuesday-Wednesday, the 12Z GFS/ECMWF/CMC and corresponding ensemble means represent the most agreeable cluster into late Tuesday. The 12Z UKMET was a weak/eastward extreme due to a somewhat broader upper trough. Other solutions suggest a depth into the 970s-980s mb by early Tuesday and possibly reaching as low as the upper 960s mb later in the day (ECMWF runs). ML models are in the weaker half of that spread. By Wednesday the CMC strays a little southward, as does the new 18Z GFS, while the 12Z ECMWF is slower to weaken the low. Fine-scale/lower-predictability details aloft will influence surface specifics. ML models develop a fair amount of timing spread by Wednesday, also tempering confidence in a specific solution at this time. At least the preferred majority dynamical model/mean scenario yields fairly good continuity for track/timing and a slightly deeper trend. Guidance exhibits fairly typical scatter for track and depth of the stronger storm forecast to reach the western Aleutians/Bering Sea by Tuesday-Wednesday. Dynamical models generally depict low pressure reaching a depth in the 950s-960s mb, with most ML models in this range as well. After Wednesday expect this system to drift eastward somewhat, most likely reaching the central/eastern Bering Sea by Friday per the model/ensemble majority. However ML models exhibit increasing spread, from reaching the west coast of the mainland to hanging back over the west-central Bering. While the 12Z GFS was within the primary guidance cluster for the parent low, it strayed a little fast with its leading front reaching the Alaska Peninsula by Thursday. The new 18Z GFS nudged somewhat slower with this front. One more uncertainty comes into the picture by next Friday as a lot of guidance is signaling western Pacific development that should reach the central Pacific by late week. Most solutions say that this development will be completely extratropical while a small minority (including the 12Z CMC) is faster with a tropical system initially farther south, making that the dominant system. Either way, signals are mixed as to whether this system will track far enough north to have a significant influence on the Aleutians. The 12Z ECMWF/ECens mean lean a bit on the northern side of the dynamical spread (near 50N latitude) but there are a couple ML models in their vicinity and the new 18Z GFS has adjusted north of earlier runs. Thus newest guidance is starting to tilt toward a little more potential for some influence on the Aleutians versus what was available at the time of forecast preparation. During Monday-Thursday a blend of the 12Z ECMWF/GFS/CMC, in order of more to less weight, represented the best ideas of guidance during from Monday into early Thursday while leaning away from less confident details of one solution or another depending on the feature. Friday introduced some of the means (12Z GEFS/CMCens and 00Z ECens) while replacing the ECMWF with the 00Z version. This kept central Pacific low pressure farther south of the Aleutians for the time being, but will monitor for additional trends/clustering in the 12Z ECMWF-ECens direction in coming cycles. ...Weather/Hazards Highlights... During the early-middle part of the week, one area of precipitation will continue moving into the mainland from the west ahead of northern Bering Sea low pressure (likely becoming less defined by Tuesday) while deepening North Pacific low pressure reaching the Gulf by Tuesday-Wednesday will spread heavier precipitation and strengthening winds from over/near the Alaska Peninsula to the Southcentral coast and Panhandle. Gap winds look to be a concern behind the surface low over the Alaska Peninsula plus Kodiak Island and the Kenai Peninsula, while strong southerly winds east of the low could also be a concern. The Days 3-7 Hazards Outlook depicts areas for high winds along much of the southern coast/Panhandle as well as heavy precipitation from the eastern Southcentral coast through the Panhandle. Meanwhile the deep western Aleutians/Bering Sea storm will bring an area of high wind potential into the Aleutians by Tuesday-Wednesday along with heavy rain potential into the eastern Aleutians/Alaska Peninsula by Wednesday (both depicted in the Hazards Outlook), with the rain focused by a leading front crossing the region. With some uncertainty in timing, an evolving Gulf wave originally embedded within the aforementioned front should push precipitation farther eastward across the southern coast and into the Panhandle later in the week. A trailing Pacific storm may increase winds/rain over the Aleutians by late week if the low track is sufficiently far north. Expect coolest anomalies to be over eastern parts of the state on Monday followed by a warmer trend from west to east, with greater coverage of above normal readings. This should particularly be the case for min temperatures, while there may be somewhat more of mix of above/below normal readings for daytime highs. Portions of the Panhandle may stay below normal for most of the 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