Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
502 FXAK68 PAFC 181350 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 550 AM AKDT Wed Sep 18 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Friday)... The strong low that tracked across the Bering Sea has crossed into southern Cook Inlet early this morning. While not as strong as it was earlier, it still is packing a punch with areas of heavy rainfall and strong winds around it. This occluded low was triple-wrapped by its front last evening as seen on satellite imagery and these multiple waves will bring the periods of enhanced rainfall today. There is a bit of cold air aloft associated with this low center which is bringing in unstable air with it. This instability kicked off a number of thunderstorms in southwest Alaska yesterday, but it is marginal whether there will be an isolated thunderstorm or two in Southcentral today as this low passes through. Most likely areas will be right under the upper low center as it tracks across southern Cook Inlet through Prince William Sound. This low is continuing to move rather quickly so it should move past the AlCan border this evening then most of the precipitation should subside for Southcentral. However there should be some stiff north to west winds behind the low which will be strongest near the coast from Kodiak to Whittier. One of the big questions will be whether these winds will be enough to keep the lower atmosphere mixed enough after the rainfall, or if all that moisture will result in widespread fog tonight into Thursday. The 12Z sounding this morning for Anchorage showed the freezing level down to 4166 ft. Therefore expect the dusting of snow along the higher peaks of the Chugach front range to hove turned into a solid line of snow or elevations above 4000 ft when the some brief breaks in the clouds develop late today and into tonight for Anchorage and the Mat-Su. In general, Thursday should see some breaks in the clouds for much of SOuthcentral,with areas farther south such as Kodiak and Homer seeing a good bit of sunshine. While there should be some sunny breaks tomorrow for most o Southcentral, the wrench in it all is that the longwave upper level trough really does not go away. Another upper level short wave looks to dig into the Susitna Valley Thursday night and stall over the Talkeetna Mountains for Friday. This might result in the Copper River Basin and Prince William Sound seeing some rain on Friday as a result of this trough. With the cold air aloft, it is possible for some of the mountain passes, mainly near Eureka and Paxson, to see snow get close to the highway on Friday. && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3)... Winds are continuing to gradually decrease as it shifts northwesterly across Southwest Alaska and the eastern Bering Sea this morning. Lingering showers will remain possible across Southwest Alaska for today with likely chances near mountains and the through the Kuskokwim Valley. Cooler air is expected to linger through the rest of this week with widespread low temperatures across Southwest Alaska hovering near freezing. A ridge currently over the western Bering Sea will build toward Southwest Alaska tonight. This should help to decrease chances for precipitation for Thursday. Current satellite imagery under the ridge indicates widespread low stratus across the Bering Sea and most recent surface observations at Atka indicate that patchy fog is developing as well. Looking ahead, there is low confidence for how much extent this fog will develop across the Aleutians and the Bering Sea. With light onshore flow and pressure building, it is possible that the Kuskokwim Delta and Bethel could have patchy fog for Thursday morning. While weak subsidence is likely for Southwest Alaska, there is a low potential for embedded shortwaves to bring brief periods of precipitation (rain, snow, or a mix) to Southwest Alaska Friday and this weekend. This should be very minor and not widespread. Farther west, a front accompanying a Kamchatka low is expected to move into the western Aleutians this afternoon. The ridge will help slow the fronts progression, keeping rain chances likely for the western Aleutians. This feature is expect to interact with a North Pacific low approaching the western Aleutians and could be the vehicle to help spread precipitation east and a track for additional troughs. With a strong ridge in place, the trough is expected to be somewhat deflected to the east and track light showery activity along the Aleutians to the Alaska Peninsula through Friday. Meanwhile, as the Kamchatka low lingers, another low will quickly follow into the western Aleutians for Thursday night, though model agreement begins to fall apart for the low trajectory and how it interacts with other synoptic features for Friday and this weekend. Models hint at continued troughing for the Aleutians, while high pressure sits in the northern Bering Sea. rux && .LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)... Latest operational models show little agreement by Friday, so will lean more on the ensemble means for the long term forecast. A broad upper low positioned over the Western Aleutians looks to slide eastward into the western Gulf by Tuesday. Upper-level jet support should remain on the south side of the low with the strongest winds at the surface to remain largely south of the Aleutians. This looks to promote a quieter period of weather for both the Bering, Southwest Alaska, and Southcentral Alaska through the weekend. Instead, drier and cooler conditions are forecast and lowering snow levels as a cooler airmass slowly makes its way from interior Alaska into Southwest Alaska by Tuesday. As the low becomes anchored over the western Gulf early next week, some potential will exist for the return of shower chances for Southcentral as easterly waves may bring scattered showers to the Copper River Basin, Prince William Sound, and Gulf coastal regions. -BL && .AVIATION... PANC...MVFR to IFR ceilings and light rain are expected through Wednesday afternoon, then VFR conditions return Wednesday night into Thursday. There is a chance for some fog Wednesday night if the winds become light and clouds clear out significantly. && $$