Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 748 PM EDT Mon Mar 17 2025 Valid 12Z Fri 21 Mar 2025 - 12Z Tue 25 Mar 2025 ...Overview... With the typical differences/continuity adjustments, guidance continues to show multiple waves reaching into the Northeast Pacific/Gulf of Alaska late this week into the start of next week. These systems will produce unsettled weather (though mostly light to moderate precipitation totals) along the southern coast and Panhandle while flow to the north/west should produce some brisk to strong winds over the Aleutians into Alaska Peninsula. Guidance continues to show amplification of the Pacific/Bering Sea upper pattern by Sunday-Tuesday as a ridge builds into the Aleutians/Bering Sea to support a digging trough over the east- central Pacific. This should ultimately lead to farther south low pressure emphasis over the eastern Pacific by next Tuesday. Meanwhile the ridge will give an eastward push to an initial trough extending to the southwestern coast from an eastern Siberia upper low. A surface ridge over high latitudes of the Arctic will help to maintain brisk easterly winds across the North Slope but the gradient may finally slacken early next week. Below normal temperature anomalies near the western coast should expand a little eastward by early next week while most other areas should see near to above normal temperatures. ...Model guidance and predictability assessment... Guidance maintains reasonable agreement and continuity with the larger scale aspects of the Pacific/Gulf of Alaska pattern, though with various issues with lower predictability details. Models have been exhibiting greater difficulty with details of the eastern Siberia upper low and the trough extending to its southeast (including the digging energy so the south from the weekend into early next week) as well as for the ridge that builds into the Aleutians and Bering Sea. For low pressure initially near the southern Gulf of Alaska, today's consensus has shifted a little southward from yesterday (thus trimming or delaying associated precipitation along the southern coast). There are still small-scale details that will take into the short range period to resolve. Upstream there is still good initial continuity and agreement with the system south of the Aleutians, and the idea that one or more leading frontal waves will reach into the northeastern Pacific/Gulf while the parent low drops southeast. By around Saturday the 12Z/18Z GFS and 12Z UKMET show a compact wave farther north near the eastern Aleutians versus most other guidance and by Sunday the UKMET shows its best defined surface low near Kodiak Island instead of farther east-southeast. A separate weaker wave could be near Kodiak Island though. Meanwhile, 12Z ECMWF/CMC runs have adjusted somewhat northward with the initial eastern Siberia upper low to reach closer to GFS/UKMET runs that have been on that side of the spread. This raises heights some within the trough extending to its southeast. Machine learning (ML) models have also been favoring some northward drift. As energy flowing underneath the low begins to dig in response to the building ridge approaching from the west, ML models in principle offer strong support for the ensemble means which have been depicting a sharpening but weakening open trough that pushes into the western mainland early next week. Latest GFS runs and the 12Z ECMWF are close to this scenario. Differences are greater just to the west, as GFS runs have tended to hold the ridge westward of other guidance including the ML models (which on average show the upper ridge axis reaching near 170W longitude by early next Tuesday). This tendency is much less pronounced in the GEFS, and the new 18Z GFS looks better. CMC runs and eventually to a lesser extent ECMWF may be overdone with eastward progress of a frontal system (aside from the leading warm front). Most ML models favor a solution closest to the ensemble means here as well. A 12Z model composite consisting of 40 percent ECMWF and the rest split among the GFS/UKMET/CMC provided a good representation of significant features early in the period, with Day 6 Sunday starting to incorporate some of the ensemble means (12Z GEFS/CMCens and 00Z ECens) to temper details that become questionable in the non-ECMWF guidance. Then by Days 7-8 early next week the forecast adjusted to 60-80 percent means with the ECMWF providing the only operational model input, given the overall ML model support for a solution closest to the means. ...Sensible weather and potential hazards... The southern coast and Panhandle should see unsettled weather for most of the period with waves reaching the Northeast Pacific/Gulf of Alaska late this week into the start of next week. These waves should gradually trend weaker with time and better low pressure emphasis will likely shift farther south over the eastern Pacific by next Tuesday. Expect mostly light to moderate precipitation while each wave may provide some wind enhancement along coastal areas and open waters. It will take additional time to resolve low-predictability specifics of the waves and thus the finer precipitation details. Flow behind the Pacific low pressure systems may produce periods of brisk to strong northerly winds over the Aleutians and into the Alaska Peninsula, most likely during Saturday-Monday. Portions of the western mainland may see scattered light snow late week into the weekend along a persistent wavy surface front that should begin to push eastward around Sunday. Flow around high latitude Arctic high pressure will maintain brisk to strong easterly winds across the North Slope through the weekend. Guidance differs on specifics of the surface pattern by early next week but suggests potential for the gradient to slacken some to yield lighter winds. Returning to the Aleutians, guidance still shows a surface ridge bringing more tranquil conditions from west to east by Sunday-Monday. Southerly winds should strengthen over the western Aleutians early next week ahead of low pressure forecast to track near Kamchatka. The upper trough extending southeast from an eastern Siberia upper low will keep temperatures somewhat below normal near the western coast of the mainland. Expect the below normal anomalies to push eastward somewhat late weekend into early next week (ultimately covering the southwestern quadrant of the mainland) as the upper trough axis moves eastward. The remainder of the mainland should trend somewhat warmer with near to above normal temperatures. Expect warmer anomalies for morning lows relative to those for daytime highs. The Panhandle should maintain a more narrow than usual temperature range with above normal morning lows and below normal highs. 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