Thursday, September23, 2021
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Marine Weather and Tides
Anchorage, AK

Version 3.4
NOTICE
3/30/2021 -- ANZ330 has been split into ANZ331 and ANZ332. Click EDIT in Marine Forecast and select your new zone.
1/26/2021 -- The West Coast Satellite images havd been updated. They now use GEOS-17.
1/1/2021 -- The 7 day forecast are now working well. Thank you NOAA for your support.

Sunrise 7:45AMSunset 7:57PM Thursday September 23, 2021 5:02 PM AKDT (01:02 UTC) Moonrise 7:39PMMoonset 10:09AM Illumination 93% Phase: Waning Gibbous; Moon at 17 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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PKZ129 Passage Canal- 410 Pm Akdt Thu Sep 23 2021
Tonight..W wind 10 kt increasing to 15 kt after midnight. Seas 2 ft. Rain.
Fri..W wind 20 kt. Gusts up to 30 kt near whittier. Seas 3 ft. Rain.
Fri night..W wind 15 kt diminishing to 10 kt after midnight. Seas 3 ft. Rain.
Sat..E wind 10 kt. Seas 2 ft.
Sat night..Variable wind 10 kt. Seas 2 ft.
Sun through Mon..W wind 15 kt. Seas 2 ft.
Tue..E wind 10 kt. Seas 2 ft.


7 Day Forecast for Marine Location Near Anchorage , AK
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location: 61.18, -149.27     debug


Area Discussion for -
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FXAK68 PAFC 231244 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 444 AM AKDT Thu Sep 23 2021

ANALYSIS AND UPPER LEVELS.

The main weather driver and system of interest continues to be an elongated low south of the Aleutians and the newly developing system at the base of its trough. The new low develops just south of Kodiak Island and makes its way north towards Prince William Sound, reaching the Sound by Thursday night. There are still quite a few inconsistencies across the models with this low in terms of speed and center location, but there seems to be good agreement again by early Friday morning. This system deepens as it pushes towards the North Gulf Coast and then stalls over PWS as it begins weakening. An upper level arctic trough moves across Southern Alaska, transporting cold northerly air across the region, and the upper level low sets up over the Anchorage/Mat- Valley area. As colder air gets wrapped around the low, the chance for snow increases for the overnight hours. Ultimately, a large part of determining the precipitation type for this type of setup during this time of year will be the intensity of the precip. Further west, ridging sets up over the Bering just ahead of a low that will end up traveling south of the Aleutians. It is unlikely that this low will have much of an impact aside from pulling pieces of energy southwards across the Bering. Thus, creating strong, northerly flow that will become increasingly gusty through the typical gaps and passes of the Eastern Aleutians and Southern AKPen.

MODEL DISCUSSION.

Models remain in good overall synoptic agreement through the short term. There is still quite a bit of struggle with the upcoming Gulf low. Track and strength of the system continue to be a non- issue amongst solutions, while center location and speed remain problematic. The NAM initially aligns well with the Canadian/EC solutions, and stays in agreement until later Thursday afternoon, with the GFS further south and west than the other three. By Thursday evening, the NAM begins to slow down, matching better with the GFS, while the Canadian/EC continue to fast track across Prince William Sound. Model agreement improves again by Friday morning, with all solutions showing the low stalling out over Prince William Sound.

AVIATION. PANC . VFR conditions and light winds will persist through late afternoon. Rain is expected by late this afternoon, with cloud ceilings dropping below 5000 ft and will likely last through the evening hours. Late tonight, cloud ceilings drop to MVFR and rain may transition to a wintery rain/snow mix.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Saturday night) .

Another significant fall storm is in store for Southcentral Alaska over the next 24 hours, bringing strong winds and high seas to Gulf coastal marine areas and another round of wintery precipitation to portions of Southcentral. A strong upper level jet streak is driving multiple surface lows northeastward into the Gulf. A short-wave trough over Bristol Bay will dig southeastward across the Alaska Peninsula and into the Gulf, leading to intensification of the low through this evening. While model guidance has struggled with determining which of the current lows will deepen, the impacts will be similar no matter which one becomes the primary low. The amplifying flow will pull the low westward toward the northwest Gulf today, then somewhere in Prince William Sound tonight as the low becomes vertically stacked.

The big change to the forecast was to go with a deeper low and farther west storm track. As a result, have strengthened winds across the Gulf waters, especially across the Kodiak Island waters northward into Cook Inlet. As arctic air advects across the Alaska Peninsula and into the Gulf tonight very strong gap winds will develop across the western Gulf. As for precipitation, the more westward low track will bring heavier precipitation to the western Kenai Peninsula and Anchorage. Short-waves tracking northeastward this morning will rotate northwestward across Southcentral this afternoon and evening as the Bristol Bay short-wave digs underneath the surface low. In the low levels, the occluded front out ahead of the deepening low will similarly rotate northwestward across the northern Gulf and Prince William Sound. While the front won't survive the journey intact as it heads inland, a surface trough will rotate across the Kenai Peninsula and Anchorage, with strong low level convergence along this trough. Because of the uncertainty in the low track as it nears Prince William Sound, there is also some question about the exact placement of the surface trough and band of heavier precipitation. However, unless the track were to somehow shift eastward, which doesn't appear likely, Anchorage should see a period of moderate to heavy precipitation this evening and into the overnight hours, especially along the mountains.

This brings us to the most challenging part of the forecast, which is precipitation type. The air mass in place out ahead of this storm is cold enough to support primarily snow inland. However, warmer air east of the low track, will warp around the north side of the low center, helping to moderate the air mass across most of the region today. The warmest air will advect across Prince William Sound and into the southeastern Copper River Basin, meaning this will be primarily a rain event for these areas. It gets a little trickier as you head north and west from Prince William Sound because the airmass will undergo less moderation. Still early in the season, solar radiation is still strong enough to produce heating near sea level, which will make it hard to produce snow during the afternoon hours. However, as heavier precipitation moves in tonight, the atmosphere will cool as the low levels first become saturated (evaporative cooling), then by the process of melting (melting snow aloft cools the atmosphere and gradually allows snow to fall lower and lower in the atmosphere). Colder air will also start to filter in from the west overnight through Friday morning. As a result, would expect a transition from rain to snow tonight through Friday morning for Anchorage and the western Kenai Peninsula, beginning along the hillside this evening and dropping to sea level by Friday morning. Snow accumulation is most likely along the Anchorage hillside and other areas above sea level. In fact, if the heavier precipitation does settle on the hillside, this could be another early season significant accumulation (of 6 inches or more). The Mat-Su looks like it will be positioned north and west of the best forcing, so even if snow does fall it shouldn't be much.

The surface low and upper trough looks to linger in the region through Friday night or Saturday, so additional light precipitation is likely. It looks like things will finally dry out by Saturday night as the trough exits into the Gulf. With a cold air mass in place, it could be another chilly night Saturday night.

SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2).

An upper level low over Southwest continues to move eastward as an upper level ridge over the Bering advances inland, leading to a clearing trend for Southwest over the next day. Residual showers will continue this morning across the Bristol Bay region before dissipating by the afternoon. Colder northerly flow will continue through the overnight hours tonight and skies will gradually clear by early Friday. A few snow showers may still linger along the foothills of the Alaska Range overnight tonight before tapering off early tomorrow. Fair conditions can be expected across Southwest into Saturday as a ridge builds over the region. An weak upper level shortwave arrives over the Kuskokwim Delta Coast Saturday evening, introducing the chance for scattered showers. Given the colder temperatures in place, there is a chance for a rain/snow mix, though little to no accumulation is expected at this time.

SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2).

The combination of a building ridge over the Bering and a low in the Gulf will keep gusty northwesterly winds in place across the central and eastern Aleutians this morning. As the Gulf low moves eastward, winds will eventually weaken and diminish overnight into early Friday. Meanwhile, an upper level wave over the western Aleutians is quickly ushering a surface low across the North Pacific, just south of the Chain. The western Aleutians can expect to see showers developing today with precipitation filling in across the Chain from west to east. By Friday morning, increasing chances for precipitation are expected across the central Bering and Pribilofs as a stronger upper level trough over Siberia drops southward. This feature will also introduce colder northerly flow to the western Bering Saturday morning and allow for a return of gusty northerly winds across the central and eastern Aleutians Saturday afternoon. The next low arrives late Saturday as a leading frontal boundary approaches the western Aleutians.

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

Gulf of Alaska . As a low over the Gulf begins to diminish, east winds will decrease with waves subsiding through Saturday. Northerly winds along the Southcentral coast will increase on Sunday and continue through Monday with the potential of gale force gusts as a low tracks east in the southern Gulf. Waves from the Barren Islands into the central Gulf will build in response.

Bering Sea . A low tracks east to the western Aleutians Sunday and will move to the southern Bering Monday. South gale force winds ahead of the low and north gale force winds behind the low will result in elevated seas measuring up to 13 ft in the southern Bering late Saturday into Sunday.

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

Models are in generally good agreement through Monday with model spread increasing by Tuesday. A continuation of the current amplified pattern is anticipated to prevail with a broad longwave trough centered over much of the mainland with multiple embedded shortwaves and a building ridge in the Bering. Colder temperatures will persist across the Southern Mainland as arctic air is drawn down from the interior due to a northerly flow aloft. A shortwave trough and surface low are expected to drop south over the eastern Bering and Aleutians from Saturday to Sunday. This has the potential of bringing small craft to locally gale force winds and rain for a brief period as it dives south. Confidence begins to diminish as models struggle to position the axis of the ridge and trough. Even with the details for individual synoptic systems less clear, there is a fairly good signal that the Pacific jet and prevailing storm track will stay relatively far south from this weekend through early next week. Global models and their respective ensemble suites have the North Pacific low moving along the Aleutian Chain Sunday and Monday and entering the southern Gulf Tuesday as it tracks around the base of the longwave trough axis. This should keep conditions much less active over the southern mainland, albeit still chilly by late September standards, with abnormally cool low level temperatures likely to remain over much of the state through nearly the entire extended period. Another low could track across parts of the Bering between Tuesday and Wednesday, although any details by this point are far from being resolved.

AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . NONE. MARINE . Storm 119 120 130 131 132 351 Gale 125 136 137 138 139 140 150 FIRE WEATHER . NONE.



SYNOPSIS AND MODEL DISCUSSION . KM SOUTHCENTRAL ALASKA . SB SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . KO MARINE/LONG TERM . TM/NS


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
ANTA2 - 9455920 - Anchorage, AK 33 mi51 min N 18 G 25 47°F 48°F987.9 hPa
46081 - Western Prince William Sound 58 mi73 min W 14 G 18 42°F 51°F1 ft985.2 hPa (-5.6)39°F
SWLA2 - 9455090- Seward, AK 74 mi51 min 52°F984.4 hPa

Wind History for Anchorage, AK
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Birchwood, Birchwood Airport, AK21 mi67 minNE 610.00 miOvercast42°F33°F71%988.9 hPa

Link to 5 minute data for PABV

Wind History from ABV (wind in knots)
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Last 24hrNW3NE4NE3CalmSE3SE3CalmCalmCalmCalmSE3CalmCalmCalmCalmCalmCalmCalmCalmS4S3CalmN5NE6
1 day agoNE5NE6N53CalmS3CalmSE3CalmS3S4S5S33CalmCalmCalmCalmCalm3NE4N3NE3NE3
2 days ago5S64SW6SW7
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SW7S11S10S11SW7S9S56E6NW7N734CalmCalmNE7NE6

Tide / Current Tables for Sunrise, Turnagain Arm, Alaska
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Sunrise
Click for Map
Thu -- 05:11 AM AKDT     0.27 feet Low Tide
Thu -- 07:45 AM AKDT     Sunrise
Thu -- 10:00 AM AKDT     34.80 feet High Tide
Thu -- 11:09 AM AKDT     Moonset
Thu -- 05:16 PM AKDT     1.91 feet Low Tide
Thu -- 07:52 PM AKDT     Sunset
Thu -- 08:40 PM AKDT     Moonrise
Thu -- 10:01 PM AKDT     34.84 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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26.120.314.79.54.80.55.517.425.531.934.832.827.721.415.810.35.72.25.517.325.73234.833

Tide / Current Tables for Sunrise, Turnagain Arm #11, Alaska
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Sunrise
Click for Map
Thu -- 05:11 AM AKDT     0.27 feet Low Tide
Thu -- 07:45 AM AKDT     Sunrise
Thu -- 10:00 AM AKDT     34.80 feet High Tide
Thu -- 11:09 AM AKDT     Moonset
Thu -- 05:16 PM AKDT     1.91 feet Low Tide
Thu -- 07:52 PM AKDT     Sunset
Thu -- 08:40 PM AKDT     Moonrise
Thu -- 10:01 PM AKDT     34.84 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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26.120.314.79.54.80.55.517.425.531.934.832.827.721.415.810.35.72.25.517.325.73234.833

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