Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
378 FXAK68 PAFC 201341 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 541 AM AKDT Thu Jun 20 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Saturday)... An upper-level shortwave and associated surface trough will move from the northern Gulf this morning over interior Southcentral by late afternoon. Mid and high level clouds will be on the increase this morning from south to north as both features advance toward the region. Showers will also move toward the coast this morning, with showers and isolated to widely scattered thunderstorms developing across the Copper River Basin and Talkeetna Mountains later today as the wave first lifts north then rotates to the west through this evening. The best chance for thunderstorms today will be along the mountains and foothill of the northern periphery of the Copper River Basin. Showers and isolated thunderstorms may also extend into the northern Susitna valley for this evening, but confidence on the extent of convection is low given the likelihood for increased cloud cover over the region by that time, helping to inhibit convective development. Southerly gap winds will also develop by late afternoon or early evening in the wake of the upper-level wave. A second upper-level wave looks to move across the region for Friday. Models continue to struggle with the strength and exact track of this feature; however, it does look like there is again the potential for isolated thunderstorms over much of the same areas as is expected today. This second feature does look to track in a more east-west then southwesterly fashion. If it does, there is a better chance for some showers, and perhaps isolated thunderstorms, to move off the Talkeetna Mountains and across the Susitna Valley for Friday evening. -TM && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS (Days 1 through 3)... A low in the North Pacific will continue to bring southerly to southeasterly winds into Southwest. This will result in widespread rain showers and a mostly cloudy sky to persist over the area today. The chance of an isolated thunderstorm, highly dependent on cloud breaks and the track of a short wave moving through the area is highest near and north of Sleetmute this evening. The chance of a thunderstorm is 20%. Elsewhere today, isolated rain showers, fog and low ceilings will be widespread in the Aleutians, the Alaska Peninsula and coastal areas from Toksook Bay to Dillingham through late this morning. Scattered rain showers are expected in the Eastern Aleutians and the Alaska Peninsula through the evening hours with drier conditions in the Central and Western Aleutians this afternoon and evening. The north Pacific low enters the Gulf resulting in a more southerly wind flow into Southwest Alaska tomorrow. The southerly flow will aid in more cloud breaks and multiple waves crossing the region. The chance of isolated thunderstorms range from 15 to 20% across the Western Alaska Range and the Kuskokwim Delta in the late afternoon and evening hours. Elsewhere, a ridge begins to build into the Western and Central Aleutians continuing the possibility of fog over the area. This ridge will slowly move eastward as a low travels south of the Western Aleutians arriving south of Adak tomorrow evening. Saturday, the ridge in the Central Aleutians moves over the Eastern Aleutians and the Alaska Peninsula through the morning hours as the North Pacific low migrates east of Adak. Southerly flow, fog, low clouds and rain will signal the departure of the ridge and the arrival of the low. Isolated rain showers and thunderstorm chances remain in the KW Delta and Western Alaska Range. -DJ && .LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)... Three main low centers on the upper air charts demonstrate the most energy through the forecast period. A slowly retrograding low over the Chukotsk Peninsula continues into Siberia. The second is a Western Bering low, the next of a series that have moving across the North Pacific, that will track across the Alaska Peninsula by midweek. The last is a low center just South of the Aleutians that will slide across the Southern Gulf of Alaska/ Eastern North Pacific for Wednesday. Most of Mainland Alaska is under a weak ridge which supports surface thermal troughs and areas of convection across the Interior for the entire forecast period. Showers are expected across Southcentral. A series of surface low and fronts bring mostly showery conditions along the Aleutians, Bering and AKPEN, spreading into Southwest Alaska through Wednesday. The next surface low from the North Pacific and its front enters the Aleutians and Bering Tuesday, and move over the Central portions by Wednesday. locally heavier precipitation and gusty winds up to gale force spread into the Central Aleutians. -Kutz && .AVIATION... PANC...Winds will start out southwesterly this morning and transition to a more southerly and even a south-southeasterly component through the day as the Turnagain Arm jet strengthens. Generally, during the afternoon and early evening hours is when the gustiest of the winds are expected which is coincident with peak day-time heating. However, there is uncertainty in the exact onset of gusty south to southeast winds. Regardless, gusts are expected to die down overnight tonight with the loss of instability and day-time heating. Pressure gradients slacken by Friday morning with the return of more light and variable winds. Meanwhile, VFR ceilings will prevail through the TAF period. The Turnagain Arm jet and associated easterly flow aloft will help to keep ceilings higher than 5,000 feet. However, there will be a number of short-waves lifting over the area through the TAF period with mid to high-level clouds expected. Precipitation should stay out of the terminal due to the downslope drying effects of the easterly to southeasterly flow aloft. The bulk of precipitation is expected to fall along Prince William Sound and the Gulf Coast. && $$