Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 649 PM EST Tue Mar 04 2025 Valid 12Z Sat Mar 08 2025 - 12Z Wed Mar 12 2025 ...Low pressure systems may bring enhanced precipitation and gusty winds into the Aleutians and coastal areas of Alaska this weekend into next week... ...Overview... Guidance shows varying ideas for upper ridging that should be northeast of the mainland as of the start of the period Saturday plus the northern periphery of another ridge progressing eastward from the eastern Bering Sea/Pacific. The latter ridge will push away an initial Gulf of Alaska/eastern Pacific trough and associated surface low just south of the mainland. Meanwhile, a strong western Bering Sea storm will send a leading front through the Bering Sea/Aleutians, with an embedded wave likely forming over the western Gulf by Monday and possibly lingering for another day or so. Guidance is split for the North Pacific/Aleutians/Bering Sea pattern by next Wednesday, but with a moderate majority suggesting a fairly vigorous system may reach the Aleutians. Overall these systems will tend to focus precipitation and potential for enhanced winds across the Aleutians and surrounding waters as well as parts of the southern coast, and to a lesser degree the western coast. ...Guidance Evaluation and Preferences... At the start of the period, the majority of dynamical and machine learning (ML) guidance clusters rather well for Gulf of Alaska low pressure as of Saturday. The 12Z UKMET is the one solution farther east, while recent GFS runs had been farther south but with the 12Z run adjusting northward to the majority. This low should lose most or all of its definition by Sunday as upstream flow pushes the supporting upper trough/low eastward. Behind this system, during Saturday-Sunday guidance exhibits fairly typical spread for western Bering Sea low pressure and the leading front that pushes across the Bering Sea and Aleutians. This favors a general model blend for the early evolution of this system. However by early next week the guidance diverges for how much upper energy and surface low pressure moves eastward across the Bering Sea. In varying ways most of the ML guidance supports the GFS/CMC/UKMET in principle, with greater eastward progression than seen in the ECMWF/ECens mean. The 12Z CMC reflected an eastward trend from the 00Z run that was closer to the ECMWF. The GFS cluster (with some lingering spread for latitude of the surface low) maintains themes from yesterday's continuity, albeit with a slightly slower/deeper reflection in today's forecast. Meanwhile ECMWF runs stray south of most guidance for the frontal wave that should form just between Kodiak Island and the Kenai Peninsula by Monday. There is still some spread among ML models, so confidence is still only moderate. Recent guidance runs have been split regarding Pacific/Aleutians evolution toward next Wednesday. ECMWF/CMC runs and their means have generally been suggesting fairly strong development from the mid-latitude Pacific into the Aleutians, with 3 of 5 00Z/06Z ML models plus the 00Z AIFS mean falling into this general cluster. On the other hand, GFS runs have been maintaining more stream separation and keeping the Pacific system more suppressed. GEFS means have been fading in and out with this potential system over the past couple days, with the 12Z run better defined than the 06Z run. 2 of 5 of the prior ML models did not show an Aleutians storm. In the 12Z cycle, one of those minority MLs switched to the ECMWF cluster and the ECens has maintained its Aleutians development. The 12Z ECMWF strayed to the fast/northern side with its surface low lifting through the western Aleutians/Bering Sea. The full array of guidance recommended depicting this system but fairly conservatively with a depth just a little stronger than the ensemble means (though the new 12Z ECens is a little deeper now). Flow over the mainland looks somewhat ill-defined at times while guidance has differed for the details of upper ridging from northeast of the mainland westward. The most common theme is for initially weak troughing to give way to the combination of an extension of the northeastern ridge and another ridge weakening as it arrives from the west. Then shortwave energy may form some degree of troughing/upper low over the southern mainland/Gulf of Alaska. Guidance preferences for the above systems led to starting the Saturday forecast with an emphasis on the 12Z GFS/ECMWF/CMC, followed by adding some 12Z UKMET for Sunday-Monday to lower ECMWF weight based on Bering Sea considerations. The forecast quickly increase ensemble mean weight (12Z GEFS/CMCens and 00Z ECens) by Tuesday-Wednesday, reaching 70 percent total late. Meanwhile GFS input was phased out by Wednesday, leaving just the CMC for the operational model component. ...Weather/Hazards Highlights... Precipitation and winds along the Panhandle and Southcentral coast late this week should steadily taper off during the weekend as low pressure over the Gulf as of early Saturday weakens. At the same time a strong western Bering Sea storm and its leading front will spread brisk to strong winds (southerly ahead of the front and westerly behind) and organized precipitation across the Aleutians and surrounding waters. Some moisture and brisk winds may reach the southwestern mainland as well. An embedded developing frontal wave that should reach a position between Kodiak Island and the Kenai Peninsula by early Monday may focus some heavier precipitation in its vicinity around Sunday-Monday while lighter totals possibly extend as far east as the Panhandle. There is a minority scenario that could lead to a farther south track of this wave and thus lower precipitation totals. Another storm potentially reaching the Aleutians around the middle of next week may produce enhanced precipitation and strong winds, but significant differences in details among guidance temper confidence in specifics at this time. The Days 3-7 U.S. Hazards Outlook currently depicts no areas of sensible weather reaching hazardous criteria on an organized scale. Moderately below normal temperatures, more likely for daytime highs, should move across the state from west to east during the weekend and into early next week. These cool anomalies will displace warmer temperatures forecast from this week into early Saturday. Some degree of upper ridging or southerly flow aloft should favor a rebound in temperatures over the western mainland during the first half of next week while a weak upper trough/low just west of the Panhandle may keep highs below normal over that region and eastern Southcentral during the early-middle part of 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