428 FXAK68 PAFC 061407 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 507 AM AKST Sun Nov 6 2022 .ANALYSIS AND UPPER LEVELS... At upper levels, a ridge of high pressure stretches from the central Bering east into the central Mainland, with its negatively tilted axis located over the eastern Bering. At 850 mb, southerly flow along the backside of the ridge advects warmer air over much of the Bering and Aleutians, while northerly flow downstream of the ridge keeps colder Arctic air over Southwest and Southcentral Alaska. An impressive atmospheric river is visible on satellite over the northern part of the state. As a result of the ridge, Southcentral and Southwest Alaska continue to see clear skies and colder temperatures. Gusty northerly winds across Southcentral continue to diminish this morning, with the strongest winds still lingering near Valdez and out of the Copper River Delta. Out west, a North Pacific low and its front are lifting across the central and eastern Aleutians into the southern Bering. The front is bringing heavy precipitation, storm force winds, and warm air along with it. The strongest winds this morning are located between Adak and Unalaska. Over the western Bering and Aleutians, another front lingers and maintains light rain over that area. && .MODEL DISCUSSION... Models are in good overall synoptic agreement through the next few days. There is consensus for a surface low to develop near Kodiak Island and the Kenai Peninsula on Wednesday morning. However, model agreement with this feature begins to diverge later in the week. The GFS tracks the low over the Gulf by Thursday morning, while the EC moves the low snug along the Gulf coast and into Prince William Sound around the same time. The exact track the low ends up taking will have an impact on the wind field and precipitation location, timing, and amounts for Southcentral. && .AVIATION... PANC...VFR conditions will persist. Gusty northerly winds will continue diminishing this morning and into the early afternoon, after which time the winds will remain light. Expect clear skies through the TAF period as a high amplitude ridge builds in from the west. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 2: Today through Monday night)... The gap winds will decrease through the day as a ridge begins to move towards Southcentral and the pressure gradient weakens. Otherwise, expect mostly clear skies and below normal temperatures through tonight. On Monday morning a frontal system will move towards Kodiak Island and the western Gulf bringing gale force easterly winds and rain and snow across Kodiak Island. This front will move north towards the Kenai Peninsula and then towards Anchorage by Monday afternoon and evening bringing initially snow along coastal locations but transitioning to rain or a mix of rain and snow. Elsewhere snow is expected with light accumulations of snow expected around the western Kenai Peninsula, Anchorage and the Matanuska valley through Monday night. The Turnagain wind will also increase on Monday, but there is model disagreement if it will bend into west Anchorage so low forecast confidence for winds on Monday afternoon through the overnight hours. The GFS has a surface low developing near the Kenai Peninsula which would keep the winds northerly across west Anchorage with down inlet flow, but other models do not form the low. This will allow the low near western Alaska to create up inlet flow and gusty southeasterly winds for west Anchorage. Finally, this front will bring warmer temperatures across much of the area ranging from the teens and 20s across the Copper River Basin and 30s elsewhere. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... One last day of clear skies and sunshine for Southwest Alaska with an upper level ridge exiting off to the east. Active weather returns with the approach of a front extending off a North Pacific low. Models have come into better agreement indicating a more rapid approach of warmer air and a quicker transition to rain than previously anticipated. This means, less snow overall is expected for most of Southwest Alaska, with highest amounts being north and west of King Salmon, including Dillingham, New Stuyahok, and Koliganek, and west towards Twin Hills, Togiak, and Platinum, with 4 to 8 inches of snow accumulation possible. Thus, Winter Weather Advisory has been issued. With a surge of warmer air, temperatures will approach freezing early Monday morning, allowing for a heavy, wet snow. Gusty southeasterly winds impacting the Bristol Bay coast during periods of heavy snow could incite some visibility issued due to blowing snow. Temperatures will rise above freezing later Monday morning, and snow will transition to rain. Mid-morning, however, with temperatures hovering around freezing, there is a chance for brief periods of freezing rain from King Salmon to Dillingham. Gusty south-southeasterly winds and areas of light precipitation will continue into Monday night, diminishing by Tuesday morning. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)... A North Pacific low lifts into the southern Bering Sea this morning. The associated front is transporting with it storm force winds, heavy precipitation, and warm air. Storm force winds are expected to track along the Eastern Aleutians and southern Alaska Peninsula today and tonight and push into Bristol Bay Monday morning. Channeling is expected to increase winds through Dutch Harbor and Cold Bay, and through the gaps and passes north of the AKPen. The low continues north through Monday morning, exiting into the Bering Strait. Winds will come down and precipitation will diminish into Monday morning. A secondary weak surface low moves over the Eastern Aleutians overnight Monday, bringing another quick shot of rain to the Eastern Aleutians and southern AKPen. && .LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)... The overall pattern progression for the long term starts off fairly clear with reasonably close model agreement, but this quickly deteriorates later in the period. On Wednesday, an upper trough will be positioned over the eastern Gulf and Alaska Peninsula (AKPen), with an associated surface low slowly moving across the eastern Gulf. This system will be shouldered by upper ridging both upstream over the Bering/Aleutians and downstream over the Yukon and Southeast AK. There is already some notable model spread for the location of the main system in play over the Gulf by this point. The ECMWF brings the surface low as far north as the Prince William Sound (PWS) on Wednesday morning, while the Canadian shows a slower progression, with the low beginning to stall out over Kodiak Island. The GFS projects a separate low wrapping in from the southeast that phases with the main upper level trough, resulting in a much stronger low persisting over the Gulf compared to the consensus all the way into Thursday morning. These differences open up a lot of forecast uncertainly already from Wednesday to Thursday, particularly in terms of winds over the Gulf and inland extent of precipitation over the southern mainland. One factor that is more clear is that the frigid air mass will be long gone by this point, with some coastal and lower elevation spots around Southwest and Southcentral likely warming back to or even above freezing by the middle of next week. Looking out farther in time, the forecast details and even the larger scale pattern resolution begins to fall apart, especially by next weekend. Large differences begin to appear for a North Pacific low expected to move approximately along the Aleutians from Thursday to Friday, with some solutions lifting the low north into the eastern Bering, while the GFS tries to plow the center straight east and south of both the Aleutians/AKPen and Gulf by Friday. Similarly significant differences are apparent for another low tracking towards the western Bering out of the Kamchatka area going into Friday and Saturday. It appears the models are struggling quite a bit with an increasingly 'blocked' large scale pattern developing late next week, where significant meridional and even retrograding (easterly) upper level flow results in slow, meandering progression of storm systems across Alaska. Needless to say, there is much left to be determined for the forecast from Friday onwards at this time. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...Winter Weather Advisory: 161. MARINE...Storm Warning: 155, 160, 165, 170, 172, 174, 180, 414. Gale Warning: 130-132, 136, 137, 150, 171, 173, 175, 176, 179, 181, 185, 352, 412, 413. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...AF SOUTHCENTRAL ALASKA...RC SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM LONG TERM...AS