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 040220 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 520 PM AKST Wed Mar 3 2021

ANALYSIS AND UPPER LEVELS.

A broad ridge building over the western Bering is forcing a more amplified pattern to set up as an elongated trough shifts eastward toward the Alaska-Yukon border. Farther west, there is an upper level low over Kamchatka gradually tracking eastward. The associated front is in place across the western Bering, transporting warmer, southerly flow northward over much of the Western Bering. Meanwhile over Southcentral, fog and low level stratus in place this morning has dissipated, and northerly outflow winds continue to aid the clearing process. A weakening low in place over the central Gulf continues to bring a few lingering showers to areas along the northern Gulf coast.

MODEL DISCUSSION.

Overall, model solutions remain in good synoptic agreement. The finer details, however, reveal several discrepancies. As the Kamchatka low moves east, its front will push inland over Southwest Thursday. Model solutions have been struggling with the location of the triple point that forms in the vicinity of Kodiak Island Friday. At this time, the NAM seems to be the outlier, keeping the developing low much weaker and broader, without a defined circulation. In contrast, the GFS/EC/Canadian solutions all advertise a well defined low spinning up and moving into the western Gulf by Friday morning. The GFS solution even suggests storm force winds on the backside of this low Friday morning, however it is the lone model to suggest this. The track this low takes will largely affect the weather over the next few days, first for Kodiak Island, and then for Southcentral. How far north or south this low tracks as it travels eastward across the Gulf will determine snowfall amounts and wind fields. At this time, confidence is high that temperatures will be cold enough to produce an all-snow event for areas across the northern Gulf, but confidence remains low with regard to the the track and position of this low.

AVIATION.

PANC . VFR conditions are expected through the afternoon with light northerly winds. Freezing fog over Cook Inlet may develop again during the overnight hours, and drift into the terminal during the early morning on Thursday, though expect fog to dissipate by late Thursday morning.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 3: Today through Saturday afternoon) .

A cold air mass remains anchored in place over Southcentral with quiet and clear conditions predominantly expected through this evening along with continued cool temperatures. Gap and outflow winds along the North Gulf Coast supported by offshore flow and cold air in place over the interior will reach their peak this evening. The strongest winds will blow through the Copper River Delta and Thompson Pass, where northerly gusts as high as 50 to 60 mph are possible through tonight. These winds should shut off rapidly during the day on Thursday as low level flow reverses and becomes onshore by Thursday evening. Areas of fog are possible once again over parts of the Mat-Su valleys after nightfall as the boundary layer decouples and temperatures near the surface cool into the single digits.

Attention from there shifts to the next system approaching from the Southwest. A triple point low is expected to form along a weakening front moving in from the Southwest, and this compact low will track somewhere just south of Kodiak Island on Thursday Night into Friday. A quick-hitting but possibly intense round of wet snow is likely for Kodiak Island north of the low center, with 3 to 6 inches of snowfall currently expected for Kodiak City late Thursday into Friday morning. However, some uncertainty persists with the track of the low, and any shift north or south could result in higher or lower totals than currently expected. As the low pushes farther east Friday, snow will spread into the eastern Kenai Peninsula along an inverted trough extending from the Gulf low. Several inches of snowfall are possible from Friday into Saturday with this band along parts of the Kenai Peninsula including Seward, Homer and Whittier, but uncertainty here remains for where the axis of heaviest snowfall will set up. Minor snowfall accumulations are also possible on Saturday morning as the band moves west over the Matanuska Valley prior to the passage of an upper level shortwave, along with another shot of much colder arctic air moving in from the northwest.

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

An active weather pattern is in store for Southwest Alaska over the next 3 days. An occluded front (warm occlusion) will approach Southwest Alaska this evening and tonight. Winds will increase overnight to gale force along the coastal Kuskokwim Delta and Nunivak Island by Thursday morning. The strongest winds will occur in and around Etolin Strait due to this area being prone to the localized funneling of south to southeasterly winds. Snow will begin falling early Wednesday morning across Nunivak Island and reach the Kuskokwim Delta by mid-morning Wednesday. The snow will then begin in Bristol Bay during the late morning hours on Wednesday and the Kuskokwim Valley by mid-afternoon. Accumulations range from 3-5" across the Kuskokwim Delta, 4-8" across Nunivak Island, 3-6" across Bristol Bay and 3-5" across the Kuskokwim Valley with locally higher amounts in spots. A Blizzard Warning has been issued from 6am AKST Wednesday morning through 6pm AKST Wednesday evening for the coastal Kuskokwim Delta and Nunivak Island as gale force winds in addition to this snow will restrict visibility to a quarter of a mile or less at times. Farther inland in the Kuskokwim Delta and Kuskokwim Valley, winds will not be as strong, though visibility can be restricted to a half of a mile at times inside of the heaviest snowbands. A Winter Weather Advisory has been issued for Bristol Bay for snow and blowing snow from 11am AKST through 11pm AKST as visibilities will be reduced to a half of a mile at times with areas in the heaviest snowbands expected to see 6" of snow within a 12 hour period.

With respect to precipitation type, there is high confidence that the precipitation will remain as snow across the Kuskokwim Delta, Kuskokwim Valley, Bristol Bay and the northern AKPEN. BUFKIT soundings consistently show temperatures remaining below freezing from the surface through the upper levels. Likewise, guidance is consistent in the warm front occluding before it reaches Southwest Alaska. This means the above freezing layer aloft will erode and thus make for below freezing temperatures from the cloud to the surface. The NAM was the warmest outlier with bringing this warmer layer farther north compared to the rest of guidance and this solution also showed the above freezing aloft become completely eroded before the onset of precipitation. Farther to the south (i.e. southern AKPEN), forecast soundings show this above freezing layer aloft not eroding completely which will allow for the snow to mix with rain at times. There is also no cold air damming present and this above layer aloft will be short-lived which inhibits the potential for freezing rain or sleet.

The snow will then gradually taper off across Nunivak Island late Thursday afternoon, Thursday evening for the Kuskokwim Delta, Thursday night for coastal Bristol Bay and Friday morning for the Kuskokwim Valley.

We are currently monitoring the potential for elevated water levels along coastal Bristol Bay Friday afternoon into Saturday. Confidence remains low at this time, however with the current pattern of widespread gale force westerly winds combined with long period 20-30ft swell behind this occluded front it cannot be ruled out.

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

An active weather pattern is in store for the Bering/Aleutians over the next 3 days. A quick moving transient ridge of high pressure will pass over the eastern Aleutians and AKPEN tonight and thus weaken the strong northwesterly gap winds throughout the coastal marine zones south of the AKPEN and eastern Aleutian Chain. A front that is currently approaching the central Aleutians is producing widespread storm force winds in the western Bering Sea with an even larger area of gale force winds. This front will continue to move eastward and completely move over land by Thursday afternoon. Areas along the Aleutian chain that are prone to the localized funneling of winds from the south will experience enhanced winds. Gusts associated with this front will reach low- end hurricane force in localized areas. Behind this front, widespread west-northwesterly gale force winds with localized areas of storm force winds will produce large westerly swell that will build to 30-35ft in spots across the central Bering Sea. The combination of widespread gale force winds with a very long fetch over the water allow for this large swell to form. This swell will remain long in period. This 30-35ft westerly swell will begin to gradually abate Thursday afternoon and will remain 20-25ft on Friday.

MARINE (Days 3 through 5: Saturday through Monday).

Bering Sea: A Northern Bering low tracks into Northwest Alaska, and its front moves across the Aleutians and Bering into Western Alaska Sat night. Widespread gale force winds and waves with some areas of storm force gusts moves into the Eastern Bering and diminishing Mon. Seas to 24 feet and heavy freezing spray subsides by Mon. Forecasts become unclear towards Mon. A new low and front moves into the Western Aleutians and Bering for Mon. Seas building to 20 feet around the Western Aleutians Mon.

Gulf of Alaska: A low exits the Gulf Sun. Strong northwesterly outflow winds from the Alaska Peninsula weaken. Model confidence is good. Widespread gale force winds and waves with an area of storm force winds near the Barren Islands and heavy freezing spray along the Alaska Peninsula diminish to small craft winds for Sun. Wave heights 22 feet over the Gulf subsiding late Sun. A new low and front enter the Western Gulf Sun night. Widespread southeasterly small craft winds spread across the Gulf. Waves building to 12 feet for Mon

LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday).

Looking at the averaged big picture, models are in pretty good synoptic agreement Sunday and Monday. An upper level low will remain across the eastern portion of Siberia and is expected to have a trough dig across the Bering and Aleutian Chain late this weekend. Ahead of that trough, ridging sets up across southcentral.

Overall this means temperatures will continue to steadily climb throughout the daytime hours Sunday and Monday across much of the region. Inland areas across southcentral could see temperatures rise above freezing for the first time since the middle of January. This pattern could potentially turn into a snowier regime for Southcentral and in particular across the Anchorage Bowl. However, many factors have to come together for Anchorage to get the snow, though, the storm track looks favorable with model guidance mostly bringing lows near and into Prince William Sound with details of each uncertain.

AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . Blizzard Warning 155. Winter Weather Advisory 161. MARINE . Storm Warning 177-179 181 185 411-414. Gale Warning 131 150 155 165 170-176 180. Heavy Freezing Spray Warning 121 130 138 160 165 180 185 414. FIRE WEATHER . NONE.



SYNOPSIS AND MODEL DISCUSSION . KO SOUTHCENTRAL ALASKA . AS SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . ED MARINE/LONG TERM . MK/SS

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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	ESE 4.1 G 5.1		30°F		1005.7 hPa (+1.5)
NKTA2 - 9455760 - Nikiski, AK	66 mi	59 min	N 5.1 G 8	19°F	29°F		1005.1 hPa (+1.3)
SWLA2 - 9455090- Seward, AK	72 mi	59 min			40°F		1001.5 hPa (+1.4)

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	66 min	SE 3	10.00 mi	Fair	8°F	4°F	83%	1005.4 hPa
Anchorage, Lake Hood Seaplane Base, AK	20 mi	66 min	SSE 3	10.00 mi	Fair	6°F	4°F	91%	1005.5 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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