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FXAK68 PAFC 101428 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 528 AM 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 the North Pacific today towards Kodiak Island and the Kenai Peninsula. 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: An active week of weather is about to get underway for southcentral Alaska. GOES water vapor imagery shows the driver of our weather lately, a deep upper-level trough across southwest Alaska, rotating about with a shortwave trough digging south through the tail of the AK Peninsula. Meanwhile, a disturbance is becoming better organized just to its south as it interacts with the shortwave. This area will continue to organize/deepen through the day as it shifts towards Kodiak Island and eventually towards the Cook Inlet. Observations across Kodiak Island show that precipitation has already begun with regional radars showing some returns across the southern Kenai Peninsula, suggesting the atmosphere is moistening and precipitation will soon begin down there as well.

Widespread precipitation will continue to spread into the Gulf Coast as a warm front lifts north throughout the day, bringing an atmospheric river into the coastal mountains, as well as warmer temperatures. Recent model trends have the low center on a more westward trajectory towards 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 late this afternoon through Sunday night. Gusty north winds could also make it down into the west side of Anchorage this evening 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 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 later today 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.

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: Today through Tuesday)...

A weakening upper low located over Bristol Bay becomes absorbed by an approaching upper trough tonight into Sunday. The end result will be the amplification of a new and stronger upper low centered near King Salmon by Sunday evening. Plentiful moisture ahead of the low and pulled in from the Gulf of Alaska will easily spread across the Greater Bristol Bay area and into the Lower Kuskokwim Valley Sunday through Monday. Moderate to heavy snow and elevated winds over Bristol Bay, with gusts up to 45 mph, will promote blizzard conditions from Dillingham to King Salmon, northeastward up to Koliganek and Iliamna. Models continue to show robust snow accumulations ranging from 6 to 18 inches. A Blizzard Warning remains in effect for Bristol Bay Sunday morning through Monday morning while a Winter Weather Advisory remains in effect for the Lower Kuskokwim Valley during the same time frame.

As low pressure wraps further inland, cooler temperatures are forecast to drop southward into the Kuskokwim Delta. Overnight lows early Monday will approach zero degrees for Bethel with wind chills dropping down into the minus twenties. Despite a lack of snowfall, the stronger winds will promote periods of blowing snow across the Kuskokwim Delta with reduced visibilities at times.
Likewise, gusty northerly winds are forecast to combine with snow showers over the Alaska Peninsula. Cold Bay in particular, and perhaps King Cove, will more than likely experience blowing snow and reduced visibilities, beginning Sunday morning and lasting into next week. Tuesday will see little change in the upper low's position. Enhanced northerly flow will prevail throughout the Bering Sea with scattered snow showers likely. A new upper low approaches the Western Aleutians by Tuesday morning.



.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...VFR conditions will prevail through this morning and potentially into this afternoon before gradual degradation later today into tomorrow. Surface winds will begin to increase out of the north in response to a low pressure moving up towards Kodiak Island. As the associated warm front approaches late today/tonight, strong ESE flow is anticipated atop the surface northerly wind... and as such, have LLWS included in the TAF package. Some uncertainty remains to the degree of blowing snow potential today as last several inches of snow across Anchorage has been low-density("fluffy"). Should blowing snow develop later today, visibilites will quickly degrade and lead to the potential for MVFR conditions.

Some snow is also possible today, but the strong ESE flow in the low/mid-levels will also lead to downsloping drier and warmer conditions. Can't rule out some brief rain Monday morning as the front pushes through and temperatures are warm.. but cross barrier flow will subside, cooling temps back down such that any precip later on Monday will be snow.

-Brown

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Kvichak
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Sun -- 12:31 AM AKST     12.86 feet High Tide
Sun -- 07:47 AM AKST     Moonrise
Sun -- 09:38 AM AKST     0.19 feet Low Tide
Sun -- 10:09 AM AKST     Sunrise
Sun -- 02:13 PM AKST     14.83 feet High Tide
Sun -- 02:50 PM AKST     Moonset
Sun -- 04:31 PM AKST     Sunset
Sun -- 10:26 PM AKST     2.91 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Kvichak, Kvichak River, Alaska, Tide feet

Levelock
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Sun -- 01:23 AM AKST     7.59 feet High Tide
Sun -- 07:47 AM AKST     Moonrise
Sun -- 10:10 AM AKST     Sunrise
Sun -- 11:23 AM AKST     0.11 feet Low Tide
Sun -- 02:49 PM AKST     Moonset
Sun -- 03:05 PM AKST     8.75 feet High Tide
Sun -- 04:29 PM AKST     Sunset
Tide / Current data from XTide NOT FOR NAVIGATION

Levelock, Kvichak River, Alaska, Tide feet

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