Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
487 FXAK68 PAFC 171345 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 545 AM AKDT Tue Sep 17 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Thursday night)... A front, which is associated with a strong low in the Bering Sea, is moving into Southcentral Alaska today. As has been the case with the storms this past week, it is moving through the area like a freight train leaving the break in between storm systems measured in hours. While the worst of the weather with this low will be in the Bering sea region, areas across Southcentral will see more rain today with this front and then widespread rain shower activity Wednesday as the cold core upper level low tracks across the region. Strong southeasterly winds will develop today into tonight for Turnagain Arm, Knik River and the Copper River as the front moves through the region. These winds will all subside when the low itself tracks across the region. However, north and west winds will increase through channeled terrain, especially along the Gulf coast as the low traverses Southcentral. This will bring some rather winds conditions from Kodiak to Whittier. While there will be some offshore winds channeled down Valdez narrows and Arm, the pattern is not conducive for significant winds there. Thursday will see this low move to the east, but there remains uncertainty as to whether Southcentral can start to see a little bit of a break in between systems that lasts more than a few hours to a day. While the next system looks to track well South of Southcentral in the Gulf, the large upper level trough remains over the mainland part of the state so that will make it difficult for good clearing to take place. && .SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days 1 through 3)... The forecast is continuing to be on track with an strong low moving across the Pribilof Islands this morning into the eastern Bering Sea toward Bristol Bay. Strong winds gusting 60 to 75 mph are possible with significant wave heights to 30 feet in the southeastern Bering Sea. A High Wind Warning has been issued for the Pribilof Islands through 7PM tonight. As this energetic system reaches Bristol Bay, an enhancement of winds along the Alaska Peninsula and Bristol Bay could elevate surf and lead to beach erosion along the coast. A High Surf Advisory continues for Bristol Bay. Strong winds will also affect areas of the Eastern Aleutians as well. A Special Weather Statement has been updated for the Eastern Aleutians and the Alaska Peninsula. Please plan accordingly and check for the latest forecast in your area. -Rux Previous Forecast Discussion: The focus in the coming days will be a low currently north of Adak, which will strengthen as it moves across the Bering Sea and into the Alaska Peninsula for Tuesday night. Much of Southwest Alaska, the Bering Sea, and the Aleutian Islands will see strong, gusty winds from this low, with the potential for high surf and coastal erosion. If you live in or will be traveling through these areas in the coming days, please stay tuned to the forecast. While there`s high confidence in the overall picture, finer details such as maximum wind gusts continue to be refined. Here are the products currently in effect: * High Surf Advisory is in effect for Bristol Bay, primarily the from the Kvichak River mouth south to Port Heiden. Confidence is lower for areas west of the Kvichak River mouth, which includes Dillingham and Togiak. * Special Weather Statement is in effect for the Pribilof Islands for strong winds and high seas. Diving into the details...the low currently north of Adak will strengthen through early tomorrow morning as it phases with a robust upper low moving in from Kamchatka. Models came into excellent agreement this morning, lending higher confidence to the forecast. While there may still be changes to the forecast if the low`s track changes, the overall strength of the system is unlikely to change. As such, expect widespread gales across much of the Bering Sea and Aleutian Islands, as well as the Southwest Alaska coastline. The strongest winds continue to be expected near the Pribilof Islands tomorrow as cold air wraps back around the low. There is a chance that gusts could come in at hurricane force, which is 75 mph or greater. However, the current forecast has gusts remaining just below this threshold as confidence is low that the strongest winds aloft will mix down to the surface. Regardless, it will be a very windy day for Pribilof Islands and surrounding waters. Strong winds are also expected across the Eastern Aleutians, Alaska Peninsula, and Bristol Bay. Winds will be southwesterly for much of Tuesday, generally parallel to the shoreline. However, as the low moves inland near Naknek/King Salmon early Wednesday morning, flow will become more westerly. This will focus wind and waves directly onshore, leading to the potential for high surf and coastal erosion. As such, a High Surf Advisory is in effect for Bristol Bay. While high surf/coastal flood products are not in effect elsewhere, there still may be minor impacts. For the south-facing shore of Kuskokwim Delta (ex: Kipnuk to Kongiganak), southeasterly onshore flow along the front on Tuesday morning could bring a brief period of higher water levels. However, this is expected to be short-lived and not as impactful as this past weekend`s storm. Similarly, the south-facing shore of Bristol Bay (from the Kvichak River mouth to Cape Newenham) could also see higher water levels from surge as there will be decently long duration of onshore winds. However, these winds will be weaker than those impacting the portion of Bristol Bay under the High Surf Advisory. Finally, the Bering side of the Alaska Peninsula (especially Nelson Lagoon) will also get their turn at strong winds from Tuesday evening through early Wednesday morning, though the winds will not be directly perpendicular to the shoreline. Overall, confidence remains low when it comes to the potential for high surf and coastal flooding due to lack of observations and modeling methods that are still relatively new. Looking ahead, northerly flow behind the departing low will usher in cooler air, with much of Southwest Alaska seeing temperatures in the 30s from Wednesday night through Thursday morning. This, in combination with weak upper level shortwaves moving in behind the low, could result in a fresh dusting of snow along area mountains and even on lower foothills. -Chen && .LONG TERM FORECAST (Days 4 through 7: Friday through Monday)... There is little agreement amongst operational models by the end of the work week on Friday. Even the ensemble means largely differ from each other during the same time period. From a pattern perspective, the general consensus is for a broad trough or upper low over the Western Aleutians and western Bering to gradually slide eastward through the beginning of next week on Monday. The operational GFS, in particular, is more aggressive with yet another strong low overspreading the Western and Central Aleutians. Ensembles eventually have the low positioned over the Gulf of Alaska by the end of the long term forecast. As far as potential impacts, the track of the trough should keep the threat of shortwaves over the Aleutians on Friday and Saturday. As the general trough continues eastward, the track of disturbances moves south of the AKPEN and eventually well south of the Gulf coast. Therefore, moderate confidence exists in somewhat of a quieter pattern setting in for the long term for Southwest and Southcentral Alaska with any upper-level jet support remaining south of mainland Alaska. What this will do however is present the opportunity for colder air to drop southward into both Southwest and Southcentral Alaska. Thus, cooler temperatures are likely along with lower precipitation chances. -BL && .AVIATION... PANC...VFR conditions persist through Tuesday morning, then MVFR ceilings and light rain are possible through Wednesday. Southeasterly Turnagain Arm winds increase by Tuesday afternoon with gusts over the terminal up to 25 kts possible, decreasing Tuesday night. && $$