Alaska Extended Forecast Discussion NWS Weather Prediction Center College Park MD 749 PM EDT Fri Mar 14 2025 Valid 12Z Tue 18 Mar 2025 - 12Z Sat 22 Mar 2025 ...Overview... Guidance continues to show a progressive storm track across the North Pacific/Aleutians and into or close to the Gulf of Alaska. A leading system should be a little south of Kodiak Island as of early next Tuesday with potential for one or more frontal waves to lift northward to the east. The next system should track near the Aleutians around midweek and continue into the northeastern Pacific/Gulf. Yet another storm is most likely to track just south of the Aleutians late in the week, but with a fair amount of timing spread. These systems will lead to the primary precipitation focus extending from the Aleutians through the southern coast and Panhandle. Meanwhile across the mainland, energy within an east-west upper trough should quickly (if not already by early Tuesday) consolidate into an upper low lingering near the Bering Strait. This feature may drift away from that position to some degree toward the end of the week. The evolution aloft should favor a warming trend over most areas away from the Bering Sea upper low and surrounding trough. Ridging at the surface and aloft north of the mainland may drift northward some by later in the week, though it should support brisk easterly winds over the North Slope for most of the week. ...Model guidance and predictability assessment... Guidance is clustered reasonably well for low pressure forecast to be south of Kodiak Island as of early Tuesday. However effects along the southern coast will ultimately depend as much on smaller-scale (thus having low predictability) wave development along the associated front. 12Z model runs are starting to show a more coherent signal of such a wave reaching west/southwest of the Panhandle by early Wednesday with continued northward progression thereafter. There could be additional waviness farther south along the front, with some QPF influence on the southern Panhandle. The 12Z ECMWF is on the eastern side of the spread for the possible Wednesday wave. Given the below average confidence in specifics, preference is to reflect the 12Z model trends but in somewhat conservative fashion. The trailing Aleutians system shows reasonable agreement into Wednesday. Some divergence arises thereafter, with CMC runs becoming notably slower/westward with the upper dynamics and surface reflection (eventually leading to more southern coast precipitation than consensus). The old 00Z ECMWF hung the system back a bit as well but the 12Z run shifted eastward to the majority. Machine learning (ML) models also do not favor the slow side of the spread, and some in fact offer potential for the main low (whether the parent low or leading frontal development) to be even faster than most of the dynamical models/means. The preferred solution continues well from yesterday's forecast with respect to both track and depth. Solutions have been more variable with the system that may influence the Aleutians toward the end of the week. ML models show a fair amount of east-west spread but agree better on a latitude around 40-50N on Friday and then a position around 50-52N and south of the Alaska Peninsula by early next Saturday. Likely due to CMC issues farther north, that model has been very suppressed with this system. ECMWF runs had been trending more suppressed but the 12Z run is closer to the ML model average that is generally best represented by the 00Z ECens mean (with the new 12Z run, arriving after forecast preparation, fairly close). Meanwhile latest GFS runs are slow/northwestern extremes for this system with minimal other support. The GEFS mean is not as slow as the GFS but still leans slower than most other solutions. Prefer greater weighting toward the 12Z ECMWF and ECens means, yielding good continuity compared to yesterday's forecast valid next Friday. Farther north, as of early Tuesday there is a guidance split over the northern mainland with the GFS/UKMET showing a deeper upper low that feeds into the midweek Bering Sea feature while most other solutions show just an elongated trough with slightly weaker upper low emphasis already over the Seward Peninsula or Norton Sound. The 06Z ECMWF AIFS offered support for the GFS cluster but the 12Z run and other 00Z ML models leaned toward the majority. An intermediate guidance average looks reasonable for resolving this discrepancy. Guidance preferences led to starting the early part of the forecast with a 12Z model composite consisting of 60 percent GFS/ECMWF and 40 percent UKMET/CMC. The forecast removed the CMC after Day 5 Wednesday due to poor comparisons to other guidance, and then phased out the GFS due to its issues with the late week North Pacific/Aleutians system. By next Saturday the blend incorporated half 00Z ECens mean, 30 percent 12Z ECMWF, and 20 percent 12Z GEFS mean. ...Sensible weather and potential hazards... Low pressure south of Kodiak Island as of early Tuesday and then one or more frontal waves to the east by Wednesday should produce an atmospheric river event focused along the southern mainland coast with some moisture reaching as far east as the Panhandle. Expect rain near the coast and heavy snow for the coastal mountain ranges. The Days 3-7 Hazards Outlook depicts the area of most impactful precipitation Tuesday-Wednesday, encompassing locations from the eastern Alaska Peninsula and Kodiak Island to the Kenai Peninsula. Precipitation specifics along the Southcentral coast and Panhandle have lower confidence due to dependence on low- predictability frontal wave details. At the same time an upstream system should spread light to locally moderate rainfall across the Aleutians. After midweek expect precipitation along most of the southern coast to trend lighter as the Aleutians system tracking into the northeastern Pacific likely stays far enough south to confine some of its moisture to the Panhandle. The next system which should track somewhat south of the Aleutians may bring light precipitation and brisk northeasterly then northerly winds. Elsewhere, anticipate at most light/scattered precipitation which would most likely be snow over parts of the western half of the mainland Tuesday-Wednesday. Windy conditions and some blowing snow are likely for the North Slope and points north due to a strong pressure gradient south of Arctic high pressure. Possible northward drift of the high may help to temper wind speeds later in the week. Tuesday may still feature below normal temperatures over a decent portion of the northern two-thirds of the state, but the forecast pattern evolution should lead to a warmer trend toward near to above normal readings over most areas thereafter. However the far western areas of the mainland should be close enough to the Bering Strait upper low and surrounding trough to remain somewhat below normal. The Panhandle may continue to see near to below normal highs but morning lows should be above normal most days. 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