Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
128 FXAK68 PAFC 241341 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 541 AM AKDT Mon Jun 24 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... Discussion: The upper level ridge continues to remain firmly entrenched over much of eastern Alaska today, but will become more elongated with a gradual shift of the upper ridge axis eastwards towards the ALCAN border. The remnants of the low Bristol Bay will retrograde back to the south then east today as the ridge over Bering Sea begins to breakdown in response to a shortwave trough lifts up across the western Aleutians into the southern Bering. Models are in good agreement with sliding the mid-level Bristol Bay low just south of Kodiak Island with weak surface low forming along the eastern side of the island. The 12Z PADQ raob shows a rather moist mid-level with steep lapse rates and drier air below 850 mb. A mid-level cloud deck is pushing through this morning but should clear out some later today and should see sufficient instability resulting in isolated to scattered thunderstorms later this afternoon. PWAT values of 0.93" (12Z raob) indicate that storms will be rather efficient rainfall producers while in their mature stage. Thunderstorms are also expected to develop once again over the foothills of the Wrangells and Talkeetna Mountains, as well as some development over the Chugach and Kenai Mountains this afternoon. Steering flow will be weak resulting in slow storm movement. PWAT values per the PAFC raob also show a 12Z value of 0.91" and a moist mid-level profile. While temperatures will be several degrees cooler today given up-inlet flow, we will still be seeing temperatures in the 70s for much of the western Kenai, Anchorage Bowl, and Mat-Su Valley. Thunderstorm potential will then shift to more of the Talkeetna Mountains (Mat-Su Valley) and the Copper River Basin tomorrow and Wednesday as the system moving into the Bering rapidly deepens and its front lifts north across the southern AKPen and western Gulf. The front will weaken significantly by the time it reaches Kodiak Island, but could see some light rain over the Island by late Wednesday into Thursday. The only other thing to mention is with a surface ridge building over the northern Gulf Tuesday and Wednesday, should see the Turnagain Arm, Knik, and Copper River Valley gap winds pick up as gradient increases. -PP && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS (Days 1 through 3)... Shower and thunderstorm chances will redevelop once more across Southwest Alaska this afternoon and evening, although convective instability values for Monday are slightly lower than on Sunday, and are greatly diminished by Tuesday. The biggest change will be the movement of the upper low to the south and east. Development of precipitation will be driven by daytime heating and the passage of any subtle shortwaves. The cold front of an approaching North Pacific low reaches the coast of Southwest Alaska Tuesday, and pushes the high pressure farther north and east into interior Alaska. Farther out west, models are have trended stronger with a low and front moving across the Western Aleutians/southern Bering through the first half of the week. Gales are expected with the leading front, but even more from the northerly winds on the backside of the low. Models indicate strengthening of the low after crossing the Aleutians, which increases confidence in widespread small craft and gales across the entire Bering late Tuesday. Some areas between the Pribilof Islands and Central Aleutians may even see storm force gusts. Gusty southerly winds can also be expected along the Kuskokwim Delta coast and across Bristol Bay on Tuesday. Mariners can expect wave heights up to 20 feet both on the Bering and Pacific sides of the Central Aleutians, and 8 to 15 foot seas across the eastern Bering. && .LONG TERM FORECAST (Days 4 through 7: Thursday through Sunday)... The long term begins with a ridging from western Canada north to the high Arctic and a deep upper level low and trough over the Bering. The ridging is likely to keep any notable systems from reaching the Mainland, with most consolidated lows remaining over the Bering or passing through the southern Gulf. For the Southern Mainland, the broad southerly flow between the trough in the west and ridging to the east will keep temperatures cooler than what has been observed recently, but will notably increase winds through the coastal terrain gaps. Shortwaves riding north on the southern periphery of the ridge may keep convection active, with afternoon and evening showers possible over the terrain. Overall, conditions will remain similar to the past week, just slightly cooler and windier. && .AVIATION... PANC...VFR conditions will persist through the TAF period. Winds will remain southerly, with brief 15 to 20 kt gusts from the Turnagain Arm possible in the afternoon hours. There will be showers and a possible isolated thunderstorm over the Chugach Mountains which are expected to remain east of the terminal. There is a light chance for low level stratus to develop a marine layer up Cook Inlet due to southwesterly winds. This currently looks unlikely, but the southwesterly winds up the inlet will continue over the next couple days. && $$