Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
167 FXAK68 PAFC 010536 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 936 PM AKDT Tue Apr 30 2024 .PREV DISCUSSION... /issued 348 PM AKDT Tue Apr 30 2024/ SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... The upper-level ridge in place over the past several days is breaking down over Southcentral as its retreats to the east. Developing southwesterly flow is advecting moisture into the region, as seen by the increasing PWAT values in the most recent soundings, as well as the expansion of low stratus across the Gulf and Alaska and patchy fog over northern Cook Inlet. A vorticity maxima embedded in the southwesterly flow on the western periphery of the ridge is helping to keep the lowest 10,000 ft or so of the atmosphere unstable. This feature, along with daytime heating across the Anchorage Bowl into the Mat-Su Valleys, is helping provide the lift necessary to produce convection across these areas. As of 3:30 pm, radar returns are showing showers beginning to develop near Hatcher Pass and along the foothills of the Chugach and Kenai Mountains. These showers will lift north tonight as the flow aloft turns more southerly; an isolated shower is not out of the question from Kenai to Anchorage and Talkeetna. A second, slightly stronger shortwave will move north across Cook Inlet early Wednesday morning. This feature will keep the potential for isolated to scattered showers in the forecast across the same locations through the first half of Wednesday. This wave will push the ridge out of the area, allowing a more potent wave and surface front to move from Kodiak on Wednesday to the Kenai Peninsula for Thursday before stalling. Showers will transition to more widespread rain across coastal locations. Showers across interior locations Wednesday afternoon/evening will taper off as advecting airmass becomes more stable. The southeasterly flow ahead of the front will also create more favorable downsloping conditions, limiting precipitation potential in the lee of mountains for Thursday. Southeasterly gap winds will increase later today as the pressure gradient along the coast tightens and the warmer airmass over the interior provides lift. These gap winds will be stronger for Wednesday as the approaching front induces a coastal ridge, further tightening the pressure gradient. Gusts of 25 to 35 mph are not out of the question across Turnagain Arm, West Anchorage and the Hillside, the Kink River Valley, and the Copper River Valley. -TM SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today through Thursday night)... A weakening ridge over southern mainland Alaska starts to get forced out of Southwest as a western Bering low moves eastward tonight. Areas of patchy fog are still possible through tomorrow morning along the Bristol Bay and Kuskokwim Delta coastline, as well as near the Pribilof Islands. A series of shortwave troughs will continue to pass over Southwest through this evening, allowing a chance for showers to occur at lower elevations with some limited instability present. Southeasterly winds will increase for much of the Bering through tomorrow morning as the low continues to move eastward. This direction of flow will help support upslope precipitation along the eastern Aleutians and Alaska Peninsula through Wednesday night. The front will start to weaken as it moves closer to Southwest, providing an opportunity for showers along Bristol Bay and the Kuskokwim Delta Wednesday night into Thursday evening. Beginning Wednesday night, a new low begins to form in the western Bering. Its front will begin extending eastward Thursday morning and reach the western Alaska coastline by Friday afternoon. Widespread precipitation mainly in the form of rain is expected across the Aleutians and Pribilofs as the front passes through. The western Aleutians will be impacted Thursday and the eastern Aleutians/Pribilof Islands will be impacted Thursday night into Friday. Recent model guidance is slowing down the front`s eastward progression starting Thursday afternoon through Friday, which could impact conditions across Southwest as the system starts to weaken Friday afternoon. BS LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)... A weakening upper level ridge slips towards the Arctic Coast and recedes into Canada through the forecast period. A very broad upper level trough stretches from the Russian Far East across the Bering and Alaska Peninsula and Gulf of Alaska. This trough is well supported by an elongated jet along the Aleutians into the Gulf throughout the weekend, while the body of the trough persists over the Northern Bering. Ensemble means maintain good confidence through Tuesday. A well clustered upper low entering Bristol Bay Saturday moves into the Gulf of Alaska for Monday before shifting to the upper Southeast Panhandle by the end of the period. This low will also initiate moderate cold air along the Alaskan West Coast and bring somewhat below normal surface temperatures across Western Alaska. The main low brings gusty Westerly winds along the Aleutians and AKPEN, with a second wind area moving along the West Coast from the North through Sunday. A large area of rainfall spreads across the Aleutians and Bering across Southwest and Southcentral Alaska, with locally heavier amounts expected across Southcentral zones through Tuesday. Another round of widespread precipitations moves over the Western Aleutians and Bering on Sunday and moves East through Tuesday. - Kutz AVIATION... PANC...Turnagain Arm winds have not developed due to weaker than expected pressure gradient. As such, light and generally northerly winds to continue tonight. Southeasterly Turnagain Arm winds still on track to pick up Wednesday afternoon. May see periods of cloud ceilings lower than 6000` tonight with diurnally driven convection continuing to diminish this evening. && $$