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PKZ170 Cape Sarichef To Nikolski Bering Side- 347 Am Akst Wed Mar 8 2023
Today..NE wind 20 kt. Seas 5 ft.
Tonight..NE wind 20 kt. Seas 5 ft.
Thu and Thu night..E wind 20 kt. Seas 5 ft.
Fri..NE wind 20 kt. Seas 5 ft.
Sat..S wind 15 kt. Seas 4 ft.
Sun..NW wind 30 kt. Seas 6 ft.

PKZ100
No data

FXAK68 PAFC 100239 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 539 PM AKST Sat Dec 9 2023

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Tonight through Tuesday)...

Key Messages:

-Light snow moving over the Anchorage, Mat Valley & Prince William Sound will taper off later this evening with an additional 1-2" of accumulation possible.

-A strong low pressure system will move up from the North Pacific Sunday and move up towards the Cook Inlet Monday Morning. Strong winds, heavy snow and whiteout conditions are possible across the greater Prince William Sound and Kenai Peninsula Regions. Several inches to a few feet of snowfall will be possible for portions of these regions.

-Additional rounds of moderate to heavy precipitation are likely to continue into the remainder of the week as several additional low pressure systems ride up into Southcentral along a deep moisture axis streaming north into the coastline.

Discussion:

A negatively tilted upper trough is now moving up into the Kenai Peninsula this evening. This is focusing synoptic lift that is beginning to shift away from the Mat Valley and Anchorage area out into the Chugach Mountains, as evidenced by a band of colder cloud tops (around -50C on IR imagery) now extending between the Prince William Sound and Talkeetnas. Light snow still lingering over the Mat Valley and Anchorage Bowl should taper off over the next few hours as the trough moves past, with perhaps an additional 1-2" possible through late this evening. Light snow will shift mostly towards eastern portions of the Chugach Range overnight as a second narrow but extensive west-east oriented trough overtakes the smaller shortwave as it lifts north into Southcentral.

Attention on Sunday then turns back to the west as a deepening area of low pressure over the North Pacific will move up near Kodiak Island, bringing widespread gale force (>34kt) and areas of storm force (>48 kt) winds to the Gulf of Alaska and Cook Inlet.
Widespread precipitation will spread from Kodiak Island up into the Gulf Coast as a warm front lifts north throughout the day, bringing an atmospheric river into the coastal mountains. Recent model trends have the low center on a more westward trajectory up the Cook Inlet.
This regime is a bit more favorable for downsloping across portions of the western Kenai northward through Anchorage and the Mat-Su Valley. Even so, strong and gusty winds developing out of the Matanuska Valley could lead to areas of blowing snow from Sunday afternoon through Sunday night. Gusty north winds could also make it down into the west side of Anchorage during the evening tomorrow and lead to localized areas of blowing snow as well.

Meanwhile, heavy precipitation characterized by several feet of snow is likely for the Kenai and Chugach Mountains. For the road system, the heaviest snow is likely for Thompson Pass and Valdez, as well as portions of the Seward Highway. An influx of warmer air is likely to lead to rain/snow mix or rain for some coastal areas such as Seward and Whittier by Monday. Winter Storm Warnings/Advisories going into effect later on Sunday have now been issued for areas covering the Kenai Peninsula and much of the greater Prince William Sound & Chugach Range. Please see information covered under the matching product for your location for further details for timing/amounts of snow, winds and reduced visibility.

While details remain uncertain, confidence is high the deep upper- level trough will drive another 2-3 areas of low pressure into southcentral Alaska through midweek. A near continuous stream of moisture will result in near continuous snow (/low-level coastal rain) for mountainous areas, with blizzard conditions possible in susceptible areas such as Thompson Pass. A big forecasting challenge with this series of systems will be the degree of 'inland' (including western Kenai and Anchorage area) precipitation as times of cross-barrier flow should subside, allowing precipitation to fill back in across the area.

-Brown/AS

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight through Tuesday)...

A weakening low centered along the Southwest Coast is the main focus of weather through tonight, as several weak shortwave troughs rotate around a common center, producing mesoscale bands of localized moderate snow showers. One particular trough tracking into Bristol Bay this evening will move over Dillingham and into interior Bristol Bay tonight, bringing the potential for a few inches of snow there, while the rest of mainland Southwest Alaska remains largely dry. Further west, cold air streaming south across the Bering Sea is providing enough instability over the relatively warm sea surface to produce persistent snow showers along the Alaska Peninsula and the Aleutian Chain as far west as Adak.

Attention shifts to an elongated low centered south of the eastern Aleutians this evening, taking aim at Southwest Alaska tonight, which has prompted the issuance of a Blizzard Warning for Bristol Bay. Early Sunday morning, snow will begin to spread across the Alaska Peninsula, combining with increasing winds to produce the potential for blizzard conditions. The heaviest snow shifts north toward Dillingham and interior Bristol Bay through the morning hours, where winds will be strongest (gusting as high as 45 mph), and conditions are most likely to be the worst. There is a wide range of snowfall amounts forecast with this storm system, ranging from 6 to 18 inches through Monday morning. The main question that remains is where the heaviest snow will fall, and thus where the longest duration of blizzard conditions will occur. There is a range in model solutions which set up the band of heaviest snow as far west as Dillingham north through Koliganek, and as far east as east of King Salmon north through Iliamna. Anywhere between, and including, either corridor may see localized snow amounts in excess of 12 inches. The current forecast depicts a middle ground solution between each extreme.

Further north in the Lower Kuskokwim Valley, 4 to 8 inches of snow are possible, with winds gusting as high as 40 mph. As a result, a Winter Weather Advisory has been issued from Sleetmute east, including Stony River and Lime Village. There is lower confidence in snow totals and winds affecting these communities coinciding in visibility reductions to one half mile or less, but there is at least moderate potential. Winds and snowfall intensity begin to diminish Monday morning, which will decrease the threat of very low visibilities.

For Monday and Tuesday, confidence decreases with how the low continues to evolve, its track, and location of precipitation.
What most possible scenarios agree on is a broad low centered somewhere over southern mainland Alaska, which will facilitate continued strong northerly flow, likely to gale force over the eastern Bering Sea, with gusty northerly winds affecting the Kuskokwim Delta. Since there is some potential that lighter snow spreads west into the Kuskokwim Delta on Monday, it is possible that blowing snow may lead to low visibilities. Another area of potential concern is the Alaska Peninsula and Aleutian Islands.
The broad low sitting over southern Alaska will cause a continued stream of increasingly colder air to be drawn south between it and high pressure in the western Bering Sea. This will lead to persistent snow shower activity along the north side of the Alaska Peninsula and along the Aleutian Chain as far west as Adak. With decreasing air temperatures, shower activity may become more vigorous and may lead to more significant reductions in visibility as gusty winds continue to blow across the region.

CQ

.LONG TERM FORECAST (Days 4 through 7)
Wednesday through Saturday

The active weather pattern across southern Alaska, the Bering Sea, and the Gulf of Alaska looks to continue through the long-term period. The main weather-maker Wednesday through Friday will be an upper-level low located in the vicinity of Bristol Bay/Alaska Peninsula (AKPEN). This low looks to slowly move eastward into the Gulf of Alaska through Friday and de-generate into an open trough then. Numerous shortwaves will rotate around this low/trough as it moves eastward. Coastal locations on the Bering side of the AKPEN, as well as the Gulf coast and coastal mountains look to receive the most precipitation in general.
Surface low tracks are uncertain at this time. There is reasonable agreement that once this upper low/trough moves east, an upper ridge will build in behind and provide a little reprieve from the unsettled conditions Thursday for Southwest Alaska and Thursday evening into Friday morning Southcentral and the Gulf. A new upper low and associated trough enter the western Bering Thursday. A strong low pressure pushes its front eastward across the Aleutians Thursday and to the coast of Southwest by Friday. This front then makes it across inland Southwest and begins to effect Southcentral by Saturday. There is uncertainty in any snow amounts due to exactly when the parent low pressure occludes and if a secondary low pressure forms along the front. In general, marine winds with the low pressure systems look to be in the small craft to gale-force category around the Gulf, Bering, and North Pacific side of the Aleutian Chain and AKPEN through Saturday.

AVIATION

PANC...The upper level short-wave responsible for the ongoing snowfall will pass through between 03Z and 06Z, leading to improving ceiling/vis. Snow showers and MVFR conditions could linger until around 12Z. After this point, surface winds will shift around to northerly and begin to strengthen ahead of a storm system near Kodiak Island. This leads to high confidence in VFR conditions beginning sometime Sunday morning. There is uncertainty in the track of the storm across the Gulf Sunday through Sunday night. At this point, it looks like the terminal will remain mostly dry due to easterly downslope flow. However, there is a chance that snow and lower ceiling/vis develop sometime Sunday afternoon or evening.

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