FXAK68 PAFC 310132 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 432 PM AKST Mon Jan 30 2023 .ANALYSIS AND UPPER LEVELS... There are a lot of different features that can be seen on satellite over the area. One of the most prominent items is the front that extends from the eastern Alaska Peninsula, through Southwest mainland Alaska and northwest of the Bering Strait. This frontal boundary is the delineation areas for rain ahead of it (to the east) and then snow behind it to the west. It is also moving slowly eastward and weakening. The upper level trough associated with it will be the one that is bringing in the possibility of light precipitation to parts of Southcentral Alaska mid-week. As far as big features, Southcentral Alaska has very little to see on satellite under the upper level ridge. However, this ridge is weak and lots of low level moisture is trapped under the inversion and keeping widespread cloud cover. Fog and stratus remains drifting around from northern Cook Inlet to Kodiak. Far to the west is the impressive looking low complex centered in the far western Bering Sea. The cold air aloft can be seen in the convective snow showers over the western Aleutians. This low will remain far t the west and the low that will move into the Bering by mid-week is just now developing along the jet stream near 44N 160E this afternoon. This low is not quite in the ideal spot off the jet stream to strengthen much, but by overnight it will be in the front left exit region of the jet streak and able to intensify more tomorrow. && .MODEL DISCUSSION... Over the next two days models are in good synoptic agreement over the region. The biggest item of note is the way they handle the saturated air over Cook Inlet and the Mat-Su regions as an upper level trough approaches the area Tuesday through Thursday and whether it will result in snowfall or not. More on that in the Southcentral part of the discussion. Wednesday night into Thursday sees an interesting model divergence in the Bering Sea with the GFS showing the main low near St Matthew Island and the NAM, GEM and EC clustered northeast of the Pribilof Islands. While the GFS is the outlier, looking a little deeper into run-to-run model consistency and model ensemble data, there is some indication that this farther north solution might be closer to the track the low will take than the farther south one that is currently favored by more of the models. Therefore the winds and precipitation through the Bering Sea are subject to be adjusted in subsequent forecasts depending on how this situation plays out. && .AVIATION... PANC...Fog and low stratus will continue to be the big concerns into Tuesday morning. By Tuesday afternoon, any residual low clouds should have dissipated leaving VFR conditions. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... Overall weather is not expected to change much through tomorrow morning. Precipitation along the Prince William Sound area will gradually diminish and fog could return to the Anchorage and Matanuska Valley areas tonight. Embedded into the upper ridge is a trough moving north into the Gulf of Alaska. This low will interact with a nearly stalled out front across western Alaska through Kodiak Island. Progression of this front will begin to edge farther into Southcentral come Tuesday night through Wednesday. Rain occurring in Kodiak will continue into tomorrow before dissipating. The interactions of these trough features riding on the western edge of an east Pacific ridge is leading to a fair amount of spatial and temporal uncertainty. Fortunately, the atmosphere aloft is generally isothermal and continuing to trend cooler enough for precipitation type to be either rain or snow. As cool air pools into the Copper River Basin and the troughs progress northeast, the lower level pressure gradient along the Chugach mountains near Valdez and Cordova could cause cool air to drain through gaps and increase northerly winds into the Gulf Tuesday night into Wednesday. Precipitation chances are expected to increase as an inverted trough develops around Cook Inlet and the front from the west moves into the Kenai Peninsula, Anchorage, and the MatSu Valleys. The timing of development and where precipitation begins is uncertain. The low in the Gulf will turn winds easterly along the northern Gulf. This could cause some degree of downsloping along the Kenai mountains and Prince William Sound, but north to northwesterly winds along the Inlet is creating another challenge to this uncertainty. It does seem likely that as the front continues to press east, weak upslope enhancement is possible on the western edge of the Kenai, Chugach, and Talkeetna mountains Wednesday. It will be difficult to have much precipitation squeezed out of this as there does not appear to much precipitable moisture advection at this time. Of the available moisture, the uplift potential could locally increase snowfall amounts. This is a dynamic situation however, so the forecast can still change. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... A complex series of lows over the western Bering have a front that shoots east, towards Norton Sound and then south across western Alaska. This front continues to bring snow, rain and snow and rain to the region. Rain has transitioned to snow along the coast and near Bethel in the Kusko Delta, though Kalskag has lagged in the transition this afternoon. Colder air will continue to filter to the south, eventually changing all of the rain over to snow this evening. Limited snow accumulation is expected to west of Dillingham, though light amounts will eventually spread east tonight and tomorrow. This front will stall over the interior tonight before it completely weakens. Clouds and cooling temperatures will be a mainstay through the middle of the week. Daytime highs will be at or slightly below freezing tomorrow, and generally below freezing Wednesday. The region should begin to dry out through the weekend with gradual clearing late tomorrow night and into Thursday. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)... A weak front will continue to slide across the central Aleutians tonight before arriving on the AKPEN tomorrow morning, accompanied by rain. The next weather system to impact the chain will be late tomorrow night as a north Pacific low lifts to the north tomorrow between Shemya and Amchitka. A gale force front will accompany this low as well as another round of southerly winds with rain. This low will lift to the northeast allowing colder air to pull in from the west again. && .LONG TERM FORECAST (Days 4 through 7: Friday through Monday)... Deterministic guidance as well as ensemble guidance depict a chaotic pattern in the upper levels for the east domain with no real defined systems and just shortwaves of varying amplitude/strength and somewhat with timing. There is some agreement on a slightly negatively tilted shortwave trough moving eastward through western Alaska to Southcentral Alaska through the day on Saturday. There looks to be weaker shortwaves passing through the southwesterly upper flow for Sunday, before a potentially more defined shortwave trough swings through for Monday. The resultant weather would be the potential for light snow for the Western Kenai Peninsula, Anchorage, and the Mat-Su Valleys, while the Eastern Kenai Peninsula, Prince William Sound, and the north Gulf Coast could see heavier precipitation from each wave on most days of the long term period. The overall flow will remain progressive with near normal temperatures and no one precipitation event lasting too long. The current unsettled and active pattern out west looks to continue throughout the long-term. The overall upper-level trough remains in the Bering Sea with a series of upper-level lows and shortwaves traversing the Bering as well as the North Pacific near the Aleutian Chain. There is, however, disagreement at the beginning of the long-term period with how guidance (both deterministic and ensembles) handles a Bering low. Where the GFS, UKMET, and Canadian ensembles have this particular low around Saint Matthew Island, ECMWF, CAN, and GFS ensembles have this low further south between Nunivak Island and potentially Bristol Bay. For now, the thinking is to go with ensemble solutions which takes a middle-ground position south of Saint Matthew Island, but not as far south as Bristol Bay. Details will become clearer as the system comes into the short-term period. There is general agreement on an expansive surface low/complex low with a few different circulation centers moving into the Bering Saturday morning with the front affecting the Aleutian Chain as early as Friday morning. Winds should only be gale-force with this system. Southwest Alaska will contend with multiple frontal system throughout the long-term; most of which are associated with the complex low in the Bering. Guidance somewhat agrees that the strongest of these fronts looks to impact Southwest on Sunday. As of now, the main precipitation- types for the Bering and Southwest look to be snow. However, the Alaska Peninsula and coastal sections of Bristol Bay could deal with some warm air intrusion with southerly flow ahead of the front for Sunday, so that is still in question and could be a challenge down the line as this system draws nearer in the short-term. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...Gale Warning: 170, 173, 174, 175, 176, 177, 178, 179, 411, 412, 413, 414. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...EZ SOUTHCENTRAL ALASKA...VR SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS LONG TERM...DN