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PKZ126 Port Valdez- 401 Am Akst Wed Mar 8 2023
Today..Variable wind less than 10 kt. Seas 2 ft.
Tonight..Variable wind less than 10 kt. Seas 2 ft.
Thu..E wind 20 kt. Seas 4 ft.
Thu night..E wind 30 kt. Seas 6 ft.
Fri..E wind 40 kt. Seas 7 ft.
Sat..E wind 30 kt. Seas 6 ft.
Sun..E wind 10 kt. Seas 2 ft.

PKZ100
No data

FXAK68 PAFC 110246 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 546 PM AKST Sun Dec 10 2023

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

Key Messages:

-A strong low pressure system will move up from Kodiak Island to the Kenai Peninsula tonight. Strong winds, heavy snow and whiteout conditions are expected or ongoing 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.

-There is still low confidence for timing, duration, type and amounts of additional precipitation potential through Wednesday.
The highest chance for continued heavy snow/rain from Tuesday to Wednesday will be focused over the eastern Prince William Sound and southern Copper River Basin.

Discussion:

A winter storm is now underway for much of Southcentral as a strong ~978 mb low now moving near Kodiak Island to the south of Shelikof Strait. A massive plume of moisture and synoptic scale lift now extends out ahead of this low near and along the low's occluding warm front, visible in the mid to upper levels as a large shield of dense, cold cloud tops arcing from Bristol Bay all the way out to the southern Yukon on GOES West satellite imagery.
Gale to storm force winds are spreading into much of the gulf and are beginning to encroach on much of the Gulf Coast, with gusts near 70 kts recently recorded at Augustine Island near the mouth of Kamishak Bay. Meanwhile, widespread moderate snowfall is now beginning to work inland, including along much of the Kenai Peninsula and out to Prince William Sound. Near whiteout conditions have been observed where snow is combining with gusty winds, including near Whittier, Homer and along the Seward Highway between Portage Valley and Seward. While strong cross-barrier flow across the Kenai and Chugach range is picking up ahead of the front, there is still some snowfall trying to spill over the terrain on to the lee side in places, including over the interior Kenai Peninsula out to Sterling and Soldotna, as well as towards the upper Hillside and far southeast Anchorage. Gusty winds have begun to pick up out of the Matanuska Valley, so far mainly resulting in minor blowing/drifting snow.

Looking to the forecast, several feet of snow remains expected 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 Monday morning. The strong east wind through the Turnagain Arm will lead to warmer temps in Portage and Girdwood as well, which may lead to a brief changeover to rain after several inches of snow has already fallen. Winter Storm Warnings/Advisories going into effect now or later this evening have 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.

For Monday night and beyond, much of the forecast remains highly in flux. Models (with one exception) have mostly trended towards a more east solution for the next low expected to lift northwest into the Gulf around the nearly stalled upper trough centered over the Alaska Peninsula, and this low should reach the coastline by Tuesday morning as it follows along a wavering frontal zone stretching over the Gulf. A near continuous stream of moisture firing into the mainly eastern sections of the Gulf coastline 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 next system will be the degree of 'inland' (including much of the Copper Basin) precipitation and the amount of warm air trying to filter into valleys that could cause some mixing with rain between Monday and Tuesday, including near McCarthy and Chitina. Farther west out towards the Kenai Peninsula and Mat-Su Valleys, the potential for additional snowfall past Monday morning has down-trended, with the majority of scenarios (now reflected in this forecast package) are keeping this region mostly dry through Tuesday night. There is a low end chance for parts of the Mat-Su Valleys and Anchorage to see several inches of snowfall if the one model solution clinging to a much farther west track for the low & atmospheric river pans out, but there appear to otherwise be very little support for this idea.

Yet another low pressure will join the parade of systems arcing north and west from the North Pacific on Wednesday morning. While details are again not clear-cut, it looks like there will be better chances this time around for light snow to spread back over to eastern parts of the outlook area, while another batch of moderate snow (and again possible mixing with rain near the coast)
moves into the Prince William Sound and Copper River Basin. Stay tuned for the forecast and for more updates to come as this very active winter pattern continues.

-Brown/AS

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

A strengthening low centered over Shelikof Strait is bringing heavy snow and blizzard conditions to locations around Bristol Bay this evening. With models in much better agreement today, there is increased confidence in the continued evolution of this storm system. Northerly winds gusting to 45 mph will continue to combining with widespread snowfall across much of Bristol Bay to produce low visibilities through Monday morning. During this time frame, an additional 3 to 9 inches of snowfall is likely, with the highest amounts for interior Bristol Bay. While Iliamna is currently not seeing any precipitation, easterly cross- barrier flow is forecast to decrease and allow for 6 to 9 inches of snowfall there tonight, though winds will diminish, meaning blizzard conditions are not expected there and will remain limited to areas further south and west. The threat of blizzard conditions end with diminishing winds and lighter snowfall on Monday morning.

Further north in the Lower Kuskokwim Valley, slightly less snow is now expected, with weaker winds forecast as well. As a result, there is a reduced likelihood for visibility reductions to one half mile or less due to blowing snow, but there is still some potential. Winds and snowfall intensity begin to diminish Monday morning, which will decrease the threat of very low visibilities.
For the Alaska Peninsula and Aleutian Islands, cold air streaming south across the Bering Sea is providing enough instability over the relatively warm sea surface to produce persistent snow showers as far west as Adak.

For Monday and Tuesday, snowfall will trend down across Southwest Alaska. Light snowfall shifts westward over western portions of the Lower Kuskokwim Valley and nudging into the eastern half of the Kuskokwim Delta as a broad low remains centered over Southcentral Alaska. However, with winds forecast to diminish, blowing snow is no longer expected to reduce visibility in these areas. Further west, strong northerly flow to gale force is expected over the eastern Bering Sea, with gusty northerly winds affecting the Kuskokwim Delta coast. Transportable snow at the surface will likely be lofted, even without new snowfall, leading to potential reductions in visibility through Wednesday, at which point winds begin to diminish.

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 cold 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. Shower activity is forecast to become more vigorous, which may lead to more significant reductions in visibility as gusty winds continue to blow across the region. Northerly flow across Southwest Alaska will also lead to decreasing temperatures through mid-week. By Tuesday night, widespread lows in the negative single digits can be expected. Combined with winds in the Kuskokwim Delta, wind chills will continue to hover around -30F.

By Wednesday, a storm force low enters the western Bering, bringing much warmer air to the western and central Aleutians.
This will bring the only rain out west during the short term forecast period.

CQ

.LONG TERM FORECAST (Days 4 through 7)
Thursday through Sunday

The long-term forecast remains on track for the continued unsettled and active pattern for Southern Alaska, the Bering Sea, and the Gulf of Alaska. For Thursday and Friday, an upper level low in the Gulf opens up into trough as it progresses eastward to Southeast Alaska. Any snow showers should be confined to the coastal mountains through Friday. Another deep trough moves eastward to the central Bering Sea and becomes stationary by Sunday. A gale to storm-force low pushes its front eastward from the Central Aleutians to the coast of Southwest Alaska through Friday. There will be a warm push of air with this front. Thus, while precipitation could start as snow ahead of the front, precipitation will quickly change to rain as the warm air works in. Precipitation type is a little more uncertain for Southwest Alaska Friday due to timing differences in when the parent low in the western Bering occludes as well as when a secondary low forms along the front. Regardless, precipitation overspreads Southwest during the second half of Friday and makes it into Southcentral Friday evening and Saturday. Coastal locations of Southcentral look to again see the most precipitation with more uncertainty for inland locations due to downslope drying flow. Cold air continues to spill into the Bering Sea Saturday and Sunday as the occluded low remains in the Bering with snow showers a good bet for Aleutian Chain. Sunday for Southcentral features a lot of uncertainty with regard to the track of a potential Gulf low.

AVIATION

PANC...Gusty northerly winds and blowing and drifting snow will be the main impact late this afternoon through the evening hours.
As loose snow becomes scoured out, it becomes difficult to say whether there will be enough snow to loft in the air and reduce the visibility above ground level. Northerly winds will then diminish overnight. There is a small chance of low level wind shear sometime between 06Z and 12Z as easterly flow strengthens along Turnagain Arm and the front range Chugach. Low level flow will rapidly diminish between 12Z and 15Z as an occluded front passes by and an upper level short-wave nears. Expect a brief period of snow, with MVFR conditions most likely. Showers will then persist in the vicinity through the day Monday. Most likely ceiling/vis will bounce up and down as snow showers move over the terminal.

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Pete Dahl Slough, Copper River Delta, Alaska, Tide feet

Eyak River entrance
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Mon -- 12:27 AM AKST     8.81 feet High Tide
Mon -- 06:33 AM AKST     3.74 feet Low Tide
Mon -- 08:57 AM AKST     Moonrise
Mon -- 09:39 AM AKST     Sunrise
Mon -- 11:50 AM AKST     12.28 feet High Tide
Mon -- 01:56 PM AKST     Moonset
Mon -- 03:32 PM AKST     Sunset
Mon -- 07:25 PM AKST     -1.41 feet Low Tide
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Eyak River entrance, Alaska, Tide feet

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