Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 656 PM EST Mon Jan 06 2025 Valid 12Z Fri Jan 10 2025 - 12Z Tue Jan 14 2025 ...Stormy pattern through the weekend with heavy precipitation and strong wind threats along the southern mainland coast, and monitoring potential western mainland storm effects around Sunday... ...Overview... Today's models and means maintain the general idea of troughing aloft with one or more embedded lows from the Bering Sea into the Pacific along with varying degrees of upper ridging downstream. Flow between the two features will carry along at least two prominent storm systems that will produce strong winds over the Northeast Pacific and possibly near the southern coast, along with focused precipitation that should be heaviest from the Kenai Peninsula through the Panhandle. The deeper of the storms, likely tracking northward along the western coast during Sunday, may produce additional areas of heavy precipitation and strong winds. Much of the state will see well above normal temperatures for most of the period, with the most pronounced anomalies expected to be during the weekend. ...Guidance Evaluation and Preferences... Primary forecast considerations centered on the two storms forecast to track from the North Pacific to the southeastern Bering Sea/western coast of the mainland, with a compromise among the 12Z ECMWF/CMC and to a lesser extent 12Z GFS preferred for their depiction during days 4-7 Friday-Monday based on dynamical guidance clustering and trends but lingering differences in machine learning (ML) guidance. Once the second and deeper of the two storms departs by next Tuesday, there are a lot of question marks about details across the Bering Sea through Pacific. For next Tuesday the preference shifted to an even blend of the ECMWF/CMC and the ensemble means (more 00Z ECens/12Z CMCens than 12Z GEFS) based on continuity and clustering for potential low pressure near 50N south of Kodiak Island and the desire to temper other details that have even lower confidence. The resulting blend yielded better than average continuity for most aspects of the forecast. The first of two North Pacific systems should reach near the eastern Aleutians by early Friday and continue into the southeastern Bering Sea thereafter. The 12Z UKMET emphasized a separate compact wave to the east of the consensus low center, favoring exclusion from the forecast. By Saturday the best dynamical/ML model clustering suggests that the low will be somewhat farther offshore the southwestern mainland compared to forecasts from the past couple days, so that is an adjustment in today's forecast. Consensus has been stable to trending slightly deeper with this system lately. There is some spread for potential waviness to the south of this system, though with minimal support for the strongly developed 18Z GFS. The second storm still looks to be the stronger one, reaching a depth a little above or below 960 mb as it reaches the eastern Aleutians/southwestern Alaska Peninsula/Bristol Bay around early Sunday. Over recent runs the ECMWF/ICON and ECens/CMCens means have been most consistent in tracking the storm rapidly northward from there, reaching the far northwestern mainland coast or thereabouts by early Monday. Latest CMC runs have adjusted to this cluster after being out of sync with storm progression in general, and the 12Z UKMET has joined as well. GFS runs have been farther south to varying degrees, with the 12Z/18Z runs somewhat less extreme than some earlier ones over the past day. While the ML models provided an excellent early signal of the storm's potential strength as far back as day 8, they have tended to be farther south than the ECMWF cluster due to suggesting more east-west mainland upper ridging (versus southerly flow). This persistence led to partial inclusion of the 12Z GFS but like yesterday yielded a solution closer to the ECMWF/CMC. New 12Z ML models seem to be starting a northward trend, at least nudging closer to the dynamical models in forecasts valid early Sunday and clustering more with the 12Z/18Z GFS thereafter (as opposed to some remaining even farther south in earlier runs). Behind this storm, details quickly become more murky within the more agreeable mean pattern by day 8 Tuesday. The one aspect with a somewhat more coherent signal is the potential for east-central into northeastern Pacific/Gulf low pressure. Recent ECMWF/CMC runs and their weaker means were close in principle, showing a surface center near 50N latitude to the south of Kodiak Island. 12Z/18Z GFS runs are weaker/faster/eastward but at least showed more of a signal than prior runs. 00Z ML models showed a lot of spread but new 12Z versions are showing more potential for faster timing than the ECMWF cluster, so that will be a possible trend worth monitoring in future guidance runs. ...Weather/Hazards Highlights... Heavy precipitation threats along the southern coast including the Panhandle will continue, with periods of strong winds over the northeastern Pacific/Gulf of Alaska toward the southern coast as well. Before the start of the current extended forecast period, the last in a series of south-to-north eastern Pacific storms should track into the Gulf of Alaska by Thursday-Thursday night and produce a period of focused rainfall and high elevation/inland snow. The Days 3-7 Hazards Chart depicts a heavy precipitation area for this event. Then the best guidance cluster still shows two North Pacific storms that may ultimately track into the southeastern Bering Sea or far western mainland by Saturday-Monday, continuing the sequence of atmospheric river events aimed at the southern coast. The transition in storm track should lead to westward expansion of meaningful precipitation back to the Alaska Peninsula, though with lower amounts than expected between the Kenai Peninsula and the Panhandle. In association with flow ahead of the storm forecast to track northward along the western mainland coast around Sunday into Monday, the Days 3-7 Hazards Chart shows another heavy precipitation area along the southeastern coast for Sunday-Monday as well as a heavy snow area over parts of the Alaska Range on Sunday. Guidance still forecasts significant five-day QPF totals (early Friday to early Wednesday) along the southeastern coast with localized maxima up to 10-15 inches of liquid possible. Parts of the western mainland may see enhanced precipitation from the weekend into early next week depending on the strength/track/timing of arriving storms. The Sunday one in particular may bring a strong wind threat that currently does not reach hazardous criteria but will require monitoring in coming days. Above to well above normal temperatures will prevail over most of the state during the period. Continued refinement of the two potential storm systems tracking toward or along the western coast of the mainland in the Saturday-Monday time frame have led guidance to show particularly warm temperature anomalies during the weekend, with some readings possibly 30F or more above normal. Passage of the second and stronger storm should quickly bring in a cooling trend from the west and south early next week. By next Tuesday some southern and western locations may decline to near or slightly below normal. 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