Marine Forecasts

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7 Day Forecast for Marine Location Near Point Possession, AK

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Area Discussion for -

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FXAK68 PAFC 301445 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 545 AM AKST Mon Nov 30 2020

ANALYSIS AND UPPER LEVELS.

A weakening storm force low positioned south of Dutch Harbor, in the left exit region of an impressive 170 kt jet, continues to be the dominant weather feature across the forecast area this morning. Temperatures overnight have cooled enough for many areas along the Aleutian Chain to transition from rain to snow with gusty winds as the front progresses eastward. Quieter conditions are set up over Southcentral Alaska, with a few lingering snow showers across the region associated with an exiting upper level shortwave. In Anchorage, the main concern this morning is fog that has set up overnight.

MODEL DISCUSSION.

Models continue to do well with the overall synoptic features through the short term. However, they are still struggling with some of the smaller features, including whether the Turnagain Arm winds will make it into Anchorage on Tuesday or not. There is also some uncertainty in whether to increase precipitation across Southcentral on the backside of the low when colder air comes in on Wednesday. Good model agreement continues over the western domain, resulting in high-res models being used to capture winds across the AKPEN.

AVIATION.

PANC . Fog will remain in the vicinity through the next few hours, with conditions improving to VFR late morning. A chance for show returns late afternoon into the evening, with lower visibility and ceilings expected. Wind shear will develop this afternoon and increase through the evening.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today through Wednesday Night) .

A very active weather pattern will impact Southcentral over the next several days. Widely scattered snow shower activity ongoing along the Gulf Coast near Cordova and in the western Susitna Valley will continue through the day, but will be increasingly enhanced by the incoming storm system through the afternoon.

A strong front is approaching the southern end of Kodiak Island this morning. After sunrise, the front will move north past Kodiak. Precipitation will begin as snow, but will mix with and then change over to rain this afternoon. Behind the front, a strong southerly flow of Pacific moisture will keep rain showers going off-and-on through Tuesday across Kodiak Island.

The front will continue tracking north this afternoon, reaching the north Gulf coast this evening. The front will cause heavy rain along the coast and precipitation will start as snow inland. Meanwhile, the front will also cause winds to increase with gusts to 60 mph along Turnagain Arm and higher elevations this evening. Gusts to hurricane force are expected with the barrier jet south of Cordova this afternoon and evening as well.

The front will move north into the mountains then drive inland across all of Southcentral tonight. Behind the front, an unseasonably warm air mass is being drawn northward into Southcentral with a tap to the tropics. As this warm air moves north, the snow will change over to rain from south to north and over most lower elevation locations as temperatures warm well into the 30s, and into the 40s in a few areas through Tuesday. In the Seward area, as much as 5 inches of precipitation, most of which falling as rain, will cause flooding concerns through Wednesday. Elsewhere, rain falling on frozen ground, specifically Tuesday morning when temperatures in many areas first rise above freezing, will lead to very slick travel conditions across Southcentral. The warm air and abundant moisture will also increase avalanche potential in many of the area mountains as well, as heavy, wet snow falls on the existing snowpack.

Meanwhile, the steady moisture-rich south to southeasterly flow will also lead to significant snowfall across portions of the Susitna Valley through Wednesday. Cool, below freezing air will persist longest in these areas. For the northern Susitna Valley, this will be because the warm air will be far away from its source, and the cold air will persist longest before being eroded. For the western Susitna Valley, plentiful upslope cooling will "artificially" keep temperatures cooler, prolonging the snowfall over the area. Thus, a Winter Storm Warning is in effect for up to 3 feet of new snow through Wednesday afternoon.

This pattern will be persistent for at least 24 hours because the parent low driving the warmth into Southcentral will be nearly stationary near the Alaska Peninsula through the day on Tuesday. On Wednesday, the cold air wrapping around the west side of the low will finally begin to move the upper level trough supporting the low eastward. The cold air will follow a typical pattern, being stuck on the west side of the Alaska/Aleutian Ranges through Tuesday, but will get through the gaps and around the southern end of those ranges on Wednesday. At some point during the day, with the exact timing still uncertain, the cold air will advance northward behind the low into Cook Inlet and eventually to the rest of Southcentral. As the cold air arrives, a brief period of snow is expected for Anchorage and the Valley, most likely Wednesday afternoon. This of course will also be associated with falling temperatures dropping well below freezing Wednesday night. The snow shower activity will take its time ending Wednesday night, especially along the coast, as the flow will remain southerly. Thus, it will remain an upslope flow, supporting the continued snow shower activity.

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

A cold and fairly active weather pattern is expected for Southwest Alaska over the next 3 days as a storm system moves northeastward along the AKPEN from this afternoon through Tuesday afternoon. This storm system will bring snow and strong winds to the Kuskokwim Valley and Bristol Bay. The heaviest snow will reach Bristol Bay this afternoon and evening. The heaviest snow for the Kuskokwim Valley will occur late this afternoon through Tuesday afternoon. Total snow accumulations of 6-11" are expected across Bristol Bay and 5-8" across the Kuskokwim Valley. Strong winds will blow this snow around and reduce visibility. The biggest visibility reductions are expected to be across the central Bristol Bay area, where visibility could be reduced to a half a mile at times. This blowing snow is expected to reach the Kuskokwim Delta, though the snow will not be as heavy there so visibility reductions will not be as much as in Bristol Bay. Winds will generally remain too light for significant blowing snow across the Kuskokwim Valley. Winter Weather Advisories have been issued for both the Kuskokwim Valley and Bristol Bay for snow and for Bristol Bay blowing snow in addition to snow. Temperatures will become much colder in the wake of this storm system as brisk northeasterly off shore flow will bring in continental polar air from the Alaskan interior.

SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3).

The weather pattern will gradually become more benign over the next 3 days across the Bering/Aleutians as the current storm system south of the Aleutians moves northeastward into the Gulf of Alaska. Gale force winds will continue across the central and eastern Bering/Aleutians today and tonight then decrease to below gale force on Tuesday with the exception of the gaps along the AKPEN. The main concern for Tuesday and Wednesday is ocean effect snow across the western AKPEN and the eastern Aleutians as strong cold air advection is expected over the warmer waters of the Bering. This pattern will make for unstable lapse rates across the eastern Bering and initiate convective snowbands that will move over the western AKPEN and eastern Aleutians.

MARINE (Days 3 through 5).

The period commences with the last vestiges of a decaying low over the Northern Gulf of AK while a new low moves from the North Pacific towards the Aleutians. First in the Gulf, winds will finally subside below gale-force as we head through the day Wed into Thu. The rest of the week will feature primarily cold air advection westerly flow with a strong low east of our area over SE Alaska.

Bering . The pattern will continue to feature rapid and dynamic cyclogenesis. On Wednesday, broad northerly flow over the Eastern Bering will yield to a new system developing south of Dutch Harbor Wed night into Thu. There is high confidence in at least gale- force winds with this low, however, storm-force winds cannot be ruled out. This low will lift north into the Central Bering by late Thu. A new low will then take its place on Fri. There is solid model agreement and moderate confidence in the pattern until the Fri system. At that point, it looks like at least gales will once again be possible, but the exact strength and location by Fri night is quite uncertain.

LONG TERM FORECAST (Days 3 through 7).

Going into the second half of this week, guidance indicates a pattern shift is ahead. Aloft, strong southerly flow pushes off to the east and exits Southcentral AK. In Southwest AK and the Bering/Aleutians, there are indications that shortwave ridging will move in behind the exit of the longwave trough. Moving into the weekend, model guidance shows this ridging moves over Southcentral and phases with a longwave high pressure ridge extending up the West Coast from high pressure in the Western US. Low pressure then returns the the Western Bering.

On the surface, high pressure exists over Mainland AK while a series of lows moves north through the Eastern Gulf of Alaska and into the Southcentral Coast, keeping trough along the coast. Low pressure also exists in the Bering. It should be noted that there is considerable spread in the models both aloft in the general pattern and at the surface with specific features. Especially with specific low pressure systems, there is too much disagreement to be able to discern what will happen in the long term. When it comes to the pattern, there is disagreement in what will happen, but guidance is at least indicating the pattern setup mentioned in the previous paragraph. Therefore, we can have some confidence in a pattern shift ahead, but there is too much uncertainty to identify specific features.


AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . Winter Storm Warning 145. Winter Weather Advisory 152 161. Flood Advisory 125. MARINE . Heavy Freezing Spray 160 180 181. Storm Warning 119 120 131 132 351 352. Gale Warning 125 128 130 136-141 150 155 160 165 170-176 179-181 413 414. FIRE WEATHER . NONE.



SYNOPSIS AND MODEL DISCUSSION . ALH SOUTHCENTRAL ALASKA . JPW SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . ED MARINE/LONG TERM . BB

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Weather Reporting Stations

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Stations	Dist	Age	Wind	Air Temp	Water Temp	Waves	Pressure	DewPt
ANTA2 - 9455920 - Anchorage, AK	25 mi	59 min	NNE 4.1 G 6	22°F	31°F		991.7 hPa
NKTA2 - 9455760 - Nikiski, AK	66 mi	59 min	E 8.9 G 8.9	23°F	37°F		990.6 hPa
SWLA2 - 9455090- Seward, AK	72 mi	59 min			44°F		991.6 hPa

Wind History for Anchorage, AK

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Airport Reports

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Airport	Dist	Age	Wind kt	Visibility	Sky/Weather	Temp	DewPt	Humidity	Pressure
Anchorage, Ted Stevens Anchorage International Airport, AK	18 mi	36 min	SE 4	10.00 mi	A Few Clouds	19°F	16°F	88%	991.5 hPa
Anchorage, Lake Hood Seaplane Base, AK	20 mi	36 min	NNE 3	10.00 mi	Fair	17°F	14°F	88%	991.9 hPa

Link to 5 minute data for PANC

Wind History from ANC (wind in knots)

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Tide / Current Tables for Fire Island, Alaska

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Tide / Current Tables for Anchorage (Knik Arm), Alaska

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Weather Map

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GEOS Local Image of Alaska    EDIT
NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
Link to Loop

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Ground Weather Radar Station Kenai, AK

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