Area Forecast Discussion
Issued by NWS Anchorage, AK
Issued by NWS Anchorage, AK
397 FXAK68 PAFC 111250 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 450 AM AKDT Sat May 11 2024 .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Monday night)... A large vertically stacked low is drifting eastward along the Alaska Peninsula and toward Kodiak Island this morning. A leading occluded front extends from just north of Kodiak Island south- southeast across the western Gulf and is lifting north and east. East to southeast winds are strengthening ahead of the front along the north Gulf coast and into Prince William Sound. These winds extend across the Kenai Peninsula, strongest through Portage Valley and other east-west oriented valleys. Short-waves along the east side of the low are tracking northward right toward the Kenai Peninsula, leading to moderate rainfall along the southeastern coast. Rainfall is much lighter as you head to the interior Kenai Peninsula due to some downward motion off the coastal mountains. Light rain also extends to the southwestern Kenai Peninsula (Kachemak Bay/Homer area) and to eastern Prince William Sound (Cordova/Valdez areas). Snow levels range from roughly 1000 to 1500 feet above sea level. Webcams show some snow through Turnagain Pass, but it is not accumulating on the roadway. Dry, but cloudy conditions can be found across the remainder of Southcentral. Localized gap winds persist, most notably in the Matanuska Valley and Copper River Valley. The low will continue to track slowly to the east-northeast, reaching the northern Gulf tonight, with the occluded front dissipating as it pushes onshore. Winds and precipitation along coastal areas will diminish tonight, with precipitation becoming more showery with time. The upper low will open into a trough as it heads inland across the southeastern Copper River Basin and into the Yukon on Sunday. This will leave a weak trough over Southcentral for Sunday. With a fairly moist airmass in place and increasing instability as some breaks develop in the clouds cover, it looks like a favorable day for some scattered afternoon/evening showers. As is typically the case, expect the bulk of these along or near the mountains. Weak ridging will build overhead on Monday while a weak low tracks south of Kodiak and into the Gulf. Kodiak will see a quick shot of light rain. There still could be some afternoon/evening convection in Southcentral, but with a lack of upper level forcing and weak instability expect shower coverage to be more isolated in nature. Temperatures will incrementally warm as we head through the next few days, with increasing sunshine and overall moderation of the chilly airmass currently in place. -SEB && .SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE ALEUTIANS (Days 1 through 3)... A stacked low embedded in a longwave trough stretching across the western Mainland and Bering Sea is now drifting about halfway between Chignik and Kodiak Island this morning. Areas of mainly rain near sea level are continuing to drift around the low into the AKPen and Bristol Bay regions, but most of this activity is staying rather light and spotty. Out along the Aleutians, a weak low moving south of the Chain is extending its front into the area, producing bands of light rain and easterly winds in small craft advisory range this morning. The weak North Pacific low and attendant front will continue to push steadily east through Sunday, eventually working into the southwest corner of the Gulf by Sunday night. Behind this feature, quiescent conditions (by Bering Sea standards) will overspread much of the Bering as a stout upper ridge moves into place. The break won`t last long, however, with a strong Kamchatka low set to push a warm front into the western Bering by Monday night. This will be a system to keep an eye on over the next day or two, as it may end up pushing unseasonably strong winds and high waves into much of the Bering Sea as it moves east early next week. Turning attention to Southwest, not much change to the pattern is expected over the next couple of days as the low entering the Gulf slowly drifts east and weakens in place. Expect a return to more pleasant but still mostly overcast conditions today as temperatures climb into the 50s over interior valleys. Afternoon showers will develop with daytime heating, especially close to the low center towards Bristol Bay this afternoon where cooler air aloft is in place. Offshore flow will weaken between Sunday and Monday as the low to the southeast continues to fall apart and the ridge over the Bering Sea starts to encroach in from the west. Afternoon shower activity will continue both days, especially closer to the Alaska Range. While far from certain, there may be just enough instability developing on Sunday afternoon to support a couple thunderstorms forming near the western Alaska range and Lower Kuskokwim Valley. This thunderstorm potential will be heavily dependent on how much cloud cover is able to clear out during the afternoon and allow for more ample solar heating. -AS && .LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)... The Alaska weather map opens with an elongated and somewhat fragmented positively tilted trough extending from the Arctic over the Eastern Mainland. The trough then curves back to the South of the Alaska Peninsula. The Northern portions drifts into the Canadian Provinces through Wednesday, while the Southern portion links up with a second system moving out of the Russian Far East. The trough becomes negatively tilted for Thursday, with an increasing negative tilt through Friday. A ridge builds over the ALCAN border through Friday. Model agreement is good through midweek, but falls apart afterwards, as the flow pattern across the region weakens. The extended forecast opens somewhat quietly as North Pacific low moves the active weather into Southeast Alaska. In the far West, the Northern Kamchatka low and front brings gusty winds and precipitation starting as snow, but quickly changing to rain across the Aleutians and Bering. The front brings locally heavy precipitation over the Central and Eastern Aleutians, AKPEN and Western Alaska. Some of this will be mixed precipitation over Western Alaska into the Interior, and trailing through Wednesday before diminishing over the AKPEN Thursday. Locally heavy rainfall moves moves over Kodiak Island and Southcentral Alaska for Thursday and across Prince William Sound and Copper River Delta through Friday. Lesser amounts of rainfall from the South reaches the Alaska Range for Friday. - Kutz && .AVIATION... PANC...VFR conditions will prevail through the TAF period as downslope flow maintains dry conditions in the lee of the Kenai and Chugach Mountains. During the morning hours, southeast winds out of Turnagain Arm will remain over the Arm and bend down the inlet coincident with the strong north to south gradient between the low pressure system over the Alaska Peninsula and higher pressure over the Mat- Su Valleys. There is a slight chance that southeast winds may clip the terminal towards this afternoon as instability increases and low- level lapse rates steepen with daytime heating. The caveat to this will be if cloud cover persists over the Mat- Su Valleys which will inhibit instability. Regardless, the gustiest of the southeast winds should remain over Turnagain Arm and the most likely scenario is light and variable winds for the terminal this afternoon/evening. && $$