380 FXAK68 PAFC 121217 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 417 AM AKDT Wed Sep 12 2018 .ANALYSIS AND UPPER LEVELS... A large blocking high centered over the Eastern Bering continues to dominate the weather pattern over most of the state this morning. The location of the high has led to persistent dry northerly (offshore) flow across the southern mainland leading to an incredible stretch of sunny skies and record warmth for the first part of the month. Communities along the Gulf Coast have seen the warmest temperatures and the most high temp records as dry northerly flow coming from the interior is warming adiabatically as it descends to the coast. Seward (75), Kodiak (74), and Kenai (70), all set new daily high temperature records yesterday, continuing the record breaking streak seen this month. Afternoon soundings over Southcentral have shown freezing levels approaching 12,000 ft, something typically seen only during the warmest mid- summer days, not mid- September. Out over the Bering, the ridge axis has shifted a bit further east allowing widespread stratus and fog to prevail over the Eastern Bering and over parts of the Southwest coastline overnight. A 990 mb low south of Adak and associated frontal system is nudging north towards the Aleutian Chain spreading rain and increased winds north into the SW Bering. There is also a line of enhanced convection that has developed along the leading cold front with lightning detection picking up numerous strikes about 250 miles southeast of Adak. && .MODEL DISCUSSION... The numerical weather models are in excellent agreement with the general pattern with little to no discrepancy. && .AVIATION... PANC...VFR conditions and light winds will persist. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... Above normal temperatures expected around Southcentral Alaska today as ridging continues to dominate to the west. Several locations have a chance to break records such as Seward and Kodiak this afternoon. The ridging will slowly track east through Friday helping to keep the majority of Southcentral Alaska under clear skies and more above average temperatures. Friday night a shortwave will approach Kodiak Island from the southwest bringing cloud cover and a chance for rain to the island. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... Areas of fog will develop and persist through the morning hours again today, especially over the Kuskokwim Delta and along the southern coast of Bristol Bay due to a weak onshore flow and a ridge of high pressure overhead. The ridge will remain in place for the next 36 hours, allowing for a continuation of warm, dry weather and early morning areas of fog, before sliding east as the synoptic pattern changes with a warm front advancing toward the AKPEN. This front will push clouds and precipitation over the AKPEN late Wednesday night and along the west coast for Thursday. The front then stalls and weakens and is soon followed by a second trough moving onshore Friday. A third occluded front then slides toward the Southwest late Friday night with more rain moving onshore for the start of the weekend. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)... Rain and southerly winds will be on the increase across the Bering through the forecast period as a series of storms ride north through the western Aleutians and into the Bering Sea. The first storm will enter the region this evening with rainfall spreading north from the central Aleutians this morning in advance of a warm front. Then, a second low will develop south of Shemya and quickly push toward Adak by the latter half of Thursday with another front pushing more precipitation across the Aleutians and into the southern and central Bering. This system will accelerate into the western Bering as it occludes and spreads its front through the Bering. Rainfall will be greatest in coverage and intensity near each front or area of low pressure. Showers will continue along the front as it moves east of the Pribilofs Friday night. By Friday night, another developing wave south of the low pushes east toward the western Aleutians. && .LONG TERM FORECAST (Days 3 through 7/Friday through Tuesday)... Long-term models continue to gradually converge on a common solution for the breakdown of the blocking ridge and accompanying return of clouds, rain and cooler temperatures to Southwest and Southcentral Alaska. The timing of large scale features in the 12Z model runs is remarkably similar. Beginning Friday, the short- wave moving up the west side of the ridge will mainly affect coastal Southwest Alaska (and more specifically the Kuskokwim Delta), with the ridge blocking rain from spreading too far inland. The next storm system tracking north into the Bering Sea will send a weakening front eastward toward mainland Alaska. Models indicate enough weakness in the ridge by this point in time to allow the front to cross Southwest Alaska Friday night through Saturday, bringing rain and cooler temperatures. However, as it tries to cross Southcentral Saturday through Sunday it will encounter some remnant of the upper level ridge. So at a minimum, the front will continue to weaken as it arrives in Southcentral. Certainly expect cloudier and cooler conditions as we head through the weekend, but rain chances are much more uncertain. Do not expect a washout by any means; rainfall will likely be light and focused along and near the mountains. Meanwhile, the Bering Sea and Aleutians can expect wet and windy conditions as a series of fairly fast moving storm systems cross the region. Looking to early next week, the models diverge on the details of the upper level flow. At this point, don't see any signs of major storm systems. Thus, after some rain over the weekend Southwest and Southcentral may settle back into drier conditions, though with more seasonable temperatures than currently being experienced. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...None. MARINE...None. && $$ SYNOPSIS AND MODEL DISCUSSION...KVP SOUTHCENTRAL ALASKA...DK SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM LONG TERM...AH/SEB