Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 658 PM EST Thu Feb 09 2023 Valid 12Z Mon Feb 13 2023 - 12Z Fri Feb 17 2023 ...High winds may affect the Alaska Peninsula/Kodiak Island/Kenai Peninsula into Monday and the Aleutians Monday-Tuesday... ...Overview... As the medium range period begins Monday, Gulf of Alaska energy and a surface low could cause lingering precipitation across the Panhandle as well as possibly high winds around the Alaska Peninsula/Kodiak Island/Cook Inlet with northwesterly flow. Meanwhile a persistent closed low is forecast to be near the Bering Strait around Monday-Wednesday while another notable closed low tracks across the northern Pacific. These features will likely merge into a single trough by Wednesday and create much below average temperatures for western Alaska, and could produce potentially strong low pressure at the surface, which could affect parts of Alaska with high winds and precipitation. This appears most likely for the Aleutians but it is becoming more likely for the southern coast as well, dependent on the eventual storm track. Yet another surface/upper low over the Bering Sea later next week could also produce a round of winds and precipitation for the Aleutians and perhaps beyond. ...Model Guidance/Predictability Assessment... The 12Z model guidance is generally agreeable regarding the pattern at the start of the period Monday, with an upper low centered near the Bering Strait (a bit deeper than guidance from the past couple of days) and another bout of energy and low pressure weakening across the Gulf of Alaska. Additionally, models show good consensus with the upper and surface lows just south of the western Aleutians in the northern Pacific on Monday. However, guidance has diverged somewhat with the track of this surface low especially by Tuesday and Wednesday. Namely, the Thursday 00Z and 06Z GFS runs and some GEFS members indicated a track of the low crossing the Aleutians and into Bristol Bay, as have recent UKMET runs. The 12Z GFS jumped back to a southerly track across the northern Pacific more in line with the more persistent ECMWF/CMC and their means, as did the 12Z GEFS mean and most ensemble members. So this latter cluster was favored for the forecast as it was the majority, and also more similar to continuity/the older model runs, so more persistent and stable. But given that some guidance indicated a Bristol Bay track, this is not certain. The general trend in the more agreeable guidance cluster was for a track a bit faster with the low pressure/frontal system and perhaps a bit farther north, closer to the Aleutians/Alaska Peninsula, and going into the Gulf of Alaska. Farther upstream, an upper low looks to develop near the Kamchatka Peninsula along with a potentially large and strong surface low. There are ample model disagreements at this time regarding how far east these features track across the Bering Sea, with the ECMWF on the farther east side with most guidance clustered farther west. Regardless energies rounding the low on the southern/eastern side, as well as frontal systems, could affect Alaska, especially the Aleutians. But the details will have to be ironed out in future forecasts. Thus the WPC forecast was based on a blend of the 12Z ECMWF/CMC/GFS and 00Z EC ensemble mean (in decreasing order of weighting) early in the period, so leaning away from the older GFS runs and UKMET. Gradually shifted the proportions of ensemble mean (especially the EC mean) guidance to greater than half by day 8 amid increasing model spread. ...Weather/Hazard Highlights... The storm track during the period will tend to focus the most active weather from the Aleutians through the southern coast and Panhandle. A surface low present in the Gulf of Alaska is forecast to direct a fetch of Pacific moisture from Southcentral Alaska and into the Panhandle early in the week. The low is expected to weaken as Monday progresses, causing precipitation to gradually lessen, while possibly strong northwesterly gap winds over portions of the Alaska Peninsula/Kodiak Island/Kenai Peninsula across the Cook Inlet on the backside of the low are forecast to die down too. Light snow chances across the central mainland are forecast to decrease as well. Meanwhile, the pattern looks to become more active across the Aleutians by Monday and shifting gradually into Southcentral Alaska and the Panhandle Tuesday-Thursday as a result of upper troughing and surface low pressure tracking eastward likely through the northern Pacific. Exact precipitation amounts and winds will vary dependent on the eventual low track, but the majority of guidance continues to suggest enhanced winds in the Aleutians at least, as well as precipitation across southern Alaska. Light snow is also a possibility farther inland. Around midweek, another round of precipitation and winds are likely to affect the Aleutians as a frontal system stemming from a Bering Sea low comes in, which could spread farther east by the latter half of the week. The upper trough developing over the western/southern mainland will lead to below normal temperatures for the first half of the week. The greatest anomalies look to stay in the southwestern mainland, where temperatures are forecast to be below normal by 20-30F and perhaps locally lower, while eastern parts of the mainland have a mix of above and below average temperatures. Temperatures should moderate closer to normal across western Alaska by Thursday-Friday. Tate Hazards: - High winds across portions of mainland Alaska, Sun-Mon, Feb 12-Feb 13. - High winds across portions of the Aleutians, Mon-Tue, Feb 13-Feb 14. - Much below normal temperatures across portions of mainland Alaska, Sun-Wed, Feb 12-Feb 14. 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