FXAK68 PAFC 190048 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 448 PM AKDT Sat May 18 2019 .ANALYSIS AND UPPER LEVELS... The previous discussion noted closed upper level lows near Adak, the Shumagin Islands, and Ketchikan. This afternoon the Adak and Ketchikan lows have weakened as they get absorbed into the Shumagin Island low which is now the main upper level low. This is still an elongated feature putting southern Mainland Alaska into easterly to southeasterly flow aloft. An easterly wave is propagating across Southcentral in this easterly flow this afternoon. While this wave is a lifting mechanism, it is not creating as much lift as the unstable atmospheric conditions from the last few days. The atmosphere over Southwest Mainland Alaska is also more stable this afternoon. && .MODEL DISCUSSION... Models are coming into much better alignment with the 12Z runs from this morning. The main model issue in the short term is the timing of easterly waves across Southcentral Alaska. The synoptic pattern is all very similar into Tuesday and then models diverge with the track of a fairly strong low approaching the Gulf of Alaska from the southwest. The good news is that models all have this feature coming from the same source region. The issue is that on Wednesday afternoon there is a spread of over 400 miles between the ECMWF solution and Canadian solution with the GFS sitting right in between. For now that GFS position and strength looks very reasonable. && .AVIATION... PANC...VFR conditions will persist. Southeast winds are expected to kick in late this afternoon through the evening but are not expected to be as strong as yesterday. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)... A frontal system associated with a low south of the Gulf will rotate from the central Gulf north and west this evening to stretch over the northern and western Gulf coasts. The front will remain stalled in this general location as the surface low tracks to the west to swings past southern Kodiak Island on Sunday. Another easterly wave and associated surface trough rotating through the eastern Gulf on Sunday will push into the northern Gulf Sunday night followed by a building surface ridge on Monday. This combination will bring a moderate surge of easterly winds into Prince William Sound and through Turnagain arm late Sunday night through Monday morning as well as southeasterly gap winds to the Copper River Basin. The onshore flow will then diminish fairly quickly as a weakening surface low track north through the western Gulf Monday night and Tuesday. The next easterly wave will take a more inland track, pushing from the Yukon Territory into the Copper River Basin and Interior Alaska Tuesday afternoon or evening. .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Saturday afternoon through Tuesday afternoon)... Showery conditions will continue across Southwest through early next week. A Gulf low will move in from the east Sun morning, bringing more widespread rain showers. Isolated thunderstorms cannot be ruled out over the inland areas of the Kuskokwim Delta and Middle Kuskokwim Valley where conditions would be most favorable on Sunday afternoon. This showery and easterly flow pattern will continue through Tuesday. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3/Saturday afternoon through Tuesday afternoon)... Generally quiet conditions are expected across the Bering through early next week. A weak area of low pressure will move into the central Bering from the north Sunday bringing showers to the Pribilofs. A second low moves into the western Bering Monday afternoon, spreading in a warm front over the western and central Aleutians. By Tuesday afternoon, a North Pacific low begins to approach the eastern Aleutians. && .MARINE (Days 3 through 5)... (Tuesday through Thursday) ...Bering Sea and the Aleutian Coastal Waters... A Pacific low (currently forecast to be in the 980 to 990 mb) will approach the east central Aleutians by Tuesday afternoon, bringing increasing winds and seas potentially to the region. However, by Wednesday, some guidance takes this low north into the eastern Bering, while others eject it towards Kodiak Island. Thus, while the potential is certainly there for small craft or even sustained gales to be added to the forecast at some point, uncertainty at this time precludes any of this being included in the forecast. Otherwise, look for nominal conditions to persist across much of the region through the period. ...Gulf of Alaska... The forecast has changed some from yesterday, as the models have come into better agreement. It now looks like a front will move into the Gulf on Wednesday, with an associated wind shift. However, winds look to remain below small craft criteria, with the net effect/concern being offshore seas increasing towards 15 feet Thursday. High pressure then regains control of the weather by Thursday evening. Forecast Confidence: Moderate && .LONG TERM FORECAST (Days 3 through 7)... The forecast picture is still becoming a little less murky for the long range portion, although it's still pretty cloudy in terms of details. The overall theme is for the guidance to have come into decent agreement with regards to a Pacific low approaching the eastern Aleutians/AKPEN by Wednesday morning, with an attendant surface front swinging north and east. That said, the agreement ends right there, as the ECMWF (European) wants to eject the low towards Nunivak Island on Thursday, where as the GFS (American) has it just east of Kodiak Island, with the Canadian Global following the GFS ides albeit further southeast. Which track this storm takes will have obvious impacts on temperatures and precipitation potential/amounts. One example of this is the forecasted 500 mb heights, and the more western European track would allow for heights being a good 60 to 80 dkm (decameters) higher, with a corresponding increase in the 850 mb temperatures. Heading into the weekend, the GFS (with support from the Canadian) and European models disagree even more with regards to where the ridge and trough axis set up, with one showing the almost exact opposite of the other. The net effect is it does look like precipitation potential will be on the increase for Southwest and Southcentral Alaska, temperatures will be highly dependent on which of the patterns develop, as upstream effects over the western Bering and Aleutians having a big effect and similar temperature concerns (although the maritime effects help reduce this variance greatly). && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...NONE. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...EZ SOUTHCENTRAL ALASKA...JR SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO MARINE/LONG TERM...PD