535 FXAK68 PAFC 110037 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 437 PM AKDT Wed Oct 10 2018 .ANALYSIS AND UPPER LEVELS... The overall large scale pattern remains similar with a long-wave trough over the Bering Sea and North-Central Pacific and a ridge over the east Pacific. A deep low which developed along the favorable eastern side of the trough yesterday is now tracking inland across Southwest Alaska with the occluded front headed inland across Southcentral. As strong pre-frontal easterly winds die down, strong and gusty south to southwest winds are moving into both Southcentral and Southwest Alaska behind the low and occluded front. These are largely driven by rapid pressure rises. Some power outages have been reported across the region due to today's winds. Steady rain is giving way to showers as cooler and more unstable air moves in behind this storm system. There are multiple low centers embedded within the trough over the Bering Sea, one near the Pribilof Islands and another just north of the western-most Aleutian Islands. The strongest winds with both of these can be found to the south of the low center, where there is a stronger jet and tighter surface pressure gradients. Showers are focused in the vicinity of these lows. Meanwhile, an upper level short-wave is beginning to dig southeastward to the south of the Aleutians. Expect this to lead to cyclogenesis at the surface some time late this afternoon. && .MODEL DISCUSSION... There are some minor, but significant differences with the next low which develops near the eastern Aleutians this afternoon and tracks across Southwest Alaska on Friday. Models vary on the strength of ridging out ahead of it over the Gulf and Southcentral Alaska as this system tracks up the west side of the ridge. This affects the eastward progression of a cold front and associated narrow band of rain. The NAM is most aggressive in shifting the front and rain eastward into Anchorage and the Mat-Su Friday afternoon while ECMWF and Canadian keep the frontal band centered just west of Cook Inlet. The GFS solution is somewhere in between. In any case, all solutions eventually do shift rain eastward, it's just a matter of whether this happens on Friday or Saturday. The current forecast largely contains just chance PoPs, so will trend toward a greater likelihood of rain and wait for future model runs to better figure out timing. && .AVIATION... PANC...The pressure rises moving up Cook Inlet this afternoon weaken as they reach Anchorage, but gusty southerly winds will persist late this afternoon into early evening. Winds will then gradually diminish later this evening through the overnight hours as the parent low moves further away and pressure gradients slacken. Another low will make it's way into the eastern Bering Sea tomorrow, which will be just enough to tighten pressure gradients and develop a Turnagain Arm wind. It looks like the terminal will be right on the northern edge of the Turnagain jet tomorrow afternoon/evening with the strongest winds remaining over the Inlet. Ceilings/vis will largely remain VFR. However, as showers move through between 00Z and 04Z today could briefly see MVFR conditions. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (through Saturday afternoon)... Rain will spread from west to east this afternoon and evening, ending somewhat quickly as the upper trough and front move northeastward. The gusty southerly winds will diminish into the evening hours, leaving much of the Southcentral with moderate southwesterly flow for the next couple days. Rain showers will linger along the north gulf coast on Thursday as a weakly unstable low-level flow is driven up against the coastal mountains. There will be a brief break in the clouds between the departing system and the incoming one. The next front will slowly make it's way from west to east across the Gulf late Thursday night into Friday. It will eventually stall out in a north/south orientation somewhere over the Kenai Peninsula. Winds will once again ramp up through Turnagain Arm, and bring some gusty winds down into the Anchorage Bowl on Friday. Rain will be likely at some point Friday, depending on where the front hangs up. The forecast is even more uncertain Friday night into Saturday when a different system develops in the central/eastern Gulf of Alaska. It's strength and track will determine how long frontal precipitation lasts on Friday night from the Kenai through the Mat-Su. The north gulf coast likely won't see a break between these two systems. Saturday will feature a good chance of rain nearly everywhere. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... Light to moderate rain will continue to fall around the Kuskokwim Valley this evening as a surface low over the region slowly drifts north. Farther south and behind the occluded front, showers and gusty westerly winds will continue across Bristol Bay and the AKPEN. THe precipitation and wind will diminish by the early morning hours as weak ridging quickly traverses the region. The broad southwesterly flow over the Bering, however, will bring another round of rain and gusty southwesterly winds to the Southwest Thursday as the next surface low entering the eastern Bering swings an occluded front toward the region. The persistent southwesterly flow will keep showers over the region through Friday as the low tracks into the interior. More widespread rain is expected Saturday as the next shortwave approaches from the west. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)... Gusty westerly winds stretching across the eastern Bering will diminish quickly this evening as a low over the Southwest continues to drift northwest and fill. Another surface low rotating around the main Bering low will across the eastern Aleutians and push into the eastern Bering early tomorrow morning. Areas of gales are expected along the Pacific side of the Aleutians east of Dutch Harbor. Rain will also overspread the eastern Aleutians and AKPEN through late Thursday. Farther west, sub-gale westerly winds are expected on the Bering side of the central Aleutians late tonight through late Thursday, as a weak disturbance rotates around the back side of the Bering low. Precipitation with this system will be more showery compared to the low over the eastern Bering. By Friday, another shortwave will slide west to east across the central Bering while a second, more organized Kamchatka low advances toward to the the western Bering. Its associated warm front will sweep across the western Aleutians with rain and gale-force winds on Friday, spreading over the central ALeutians by early Saturday morning. && .LONG TERM FORECAST (Days 4 through 7: Saturday Night through Wednesday Night)... A strong low located south of Adak on Saturday night is forecast to make its way towards mainland Alaska, and will be the cause of much of the active weather across the area through the long-term. The long-term models are all in impressive agreement on the forecast behavior of the low, which adds confidence to the forecast that is not commonly there. The low center is expected to track eastward but remain well south of the Aleutians until it crosses the Alaska Peninsula near Cold Bay during the day Monday. The low will be a large one, and as such will impact many communities well away from the center. The front wrapping around the low pressure center is expected to approach and move in to Southwest Alaska on Sunday evening, despite the low center still located south of Cold Bay at that time. This is testament to the large area that will be affected by the low. Overnight Monday night into Tuesday, the low center will track northward to near Kuskokwim Bay, slowly weakening as it goes, then will remain nearly stationary over the Kuskokwim Delta through Wednesday night. Across Southcentral, rain ongoing from a low that will impact the area during the day Saturday will diminish Saturday night. High pressure briefly moves in during the day Sunday, which looks to be by far the nicer of the two weekend days. Winds will be on the increase through the gaps late in the day Sunday into the night, as a strong warm front lifts northward into the area. The rain, heavy at times will persist across much of Southcentral through the day on Monday, and continue into Monday night. With the stationary low over Southwest Alaska keeping the overall atmospheric flow out of the south to southwest Tuesday and Wednesday, a continuation of cloudy and showery conditions is likely to persist. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...Gale 130-132 138-140 150 155 172. && $$ SYNOPSIS AND MODEL DISCUSSION...SEB SOUTHCENTRAL ALASKA...MTL SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM LONG TERM...JW