Marine Weather and Tides
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 7:28AM||Sunset 8:20PM||Thursday September 16, 2021 10:50 AM AKDT (18:50 UTC)||Moonrise 5:57PM||Moonset 12:00AM||Illumination 77%|
7 Day Forecast for Marine Location Near St. George, AKHourly EDIT Help
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FXAK68 PAFC 161307 AFDAFC
Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 507 AM AKDT Thu Sep 16 2021
ANALYSIS AND UPPER LEVELS.
An elongated upper trough remains sprawled out between the western Gulf and out over much of the Bering/Aleutians this morning. Two embedded features stand out on GOES-17 satellite products, with the first consisting of a stacked low west of the Pribilofs drifting south towards the Eastern Aleutians. This system is in the process of merging with a robust 180 kt upper jet streak and secondary upper level trough located just south of the central Aleutians, with the combined system on track to continue accelerating into the the North Pacific this morning. Rapid pressure rises coupled with a strong pressure gradient on the back side of this system are supporting westerly gale force winds, mainly along and south of the Western Aleutian Chain.
The second feature of note aloft is crossing into the Gulf from the AKPen as a separate shortwave trough, and this shortwave is supporting a strengthening and maturing low at the surface just east of Kodiak Island. Gale force winds out of the east to northeast are developing along and north of the low's occluding front that currently extends out from the low across the central Gulf, including areas near the Barren Islands, southern Cook Inlet and through Shelikof Strait. A deck of mid to upper level cloud cover along with areas of rain is expanding slowly north into mainly southern portions of Southcentral. The heavier and more steady rainfall has thus far been limited to areas with support from upslope flow ahead of the front along the western Alaska Range and eastern Kenai Peninsula.
Models are in excellent agreement for impactful synoptic features through the start of next week, and the overall forecast confidence for this package is high. One lingering forecast challenge will involve the extent that precipitation will work into interior parts of Southcentral as a couple subtle easterly waves move along the Gulf low's front into the Prince William Sound area from this afternoon through Friday morning. Low temperatures may also prove difficult to resolve for both Saturday and Sunday morning, with the first potential outbreak of cold air of the season and attendant threat for sub-freezing temperatures at low elevations over parts of Southcentral and the interior Southwest this weekend. Nighttime temperatures will be highly sensitive to the degree of clearing and how quickly northerly winds subside between Friday night and Sunday morning, with any calmer winds and clearing favoring colder morning lows.
AVIATION. PANC . VFR conditions and light north winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Saturday night) .
. Widespread frost or freeze likely this weekend .
A gale force low centered just east of Kodiak Island this morning will drift out into the central Gulf this today then rapidly weaken over the southern Gulf tonight as the long-wave trough amplifies and jet support shifts well off to the south. Weak short-waves east of the upper low center will push the occluded front northward through this evening, causing winds along the north Gulf coast to continue to strengthen. Weak waves moving along the front will tighten up pressure gradients further, so have upped to a storm force warning between Hinchinbrook Island and Cape Suckling this evening. Winds will then gradually diminish across the Gulf waters overnight tonight through Friday.
The last remnants of the upper level low which has been over Southwest Alaska the past few days will lift northward toward interior Alaska today. A band of rain over the Susitna Valley will fall apart as the upper wave exits midday. Otherwise, the primary rainmaker is the storm over the Gulf. The bulk of heavy rain with this storm will be confined to the Gulf coast and Prince William Sound, largely due to the fact that the occluded front remains over the Gulf and never pushes onshore. Strong low level east to northeast winds will favor western Prince William Sound for the heaviest rain. As the upper low shifts over the central Gulf tonight, short-waves on the north side will rotate across the southern tier of Southcentral. This could spread some light rain over the coastal mountains, with a chance of rain extending from the western Kenai to Anchorage, the Matanuska Valley, and to the southern to western Copper River Basin. It then looks like some weak deformation aloft sets up on Friday, as the westerly moving waves meet easterly moving waves dropping down the front of an upstream ridge. This will extend the chance of rain through Friday, centered along a line from the Talkeetna Mountains southward to the front range Chugach in Anchorage and down to the Kenai Mountains.
A much more significant Arctic trough will dive southeastward across western Alaska Friday, then swing eastward across the mainland and Gulf Friday night through Saturday. This will help kick out all of the rain and usher in drier and colder air. In fact, this looks like the coldest airmass of the season to move over Southcentral. Initially, the biggest impact will be strong gusty gap winds due to tight surface pressure gradients between the exiting low over the eastern Gulf and a strong ridge of high pressure building into mainland Alaska from the Bering Sea. The passage of the upper trough along with the cold air advection will further enhance winds. The strongest winds will be over the western Gulf waters and gaps along the south side of the Alaska Peninsula. Secondarily, winds will also kick up through channeled areas along the north Gulf coast and Prince William Sound.
Winds will quickly die down Saturday night as high pressure moves overhead. With mostly clear skies and light or calm winds inland, there is potential for widespread freezing temperatures. For areas that don't get quite that cold, a frost is likely. The one wild card is whether there will be any clouds early or late in the night, as the upper trough is still exiting eastward during the evening, while a new storm is tracking quickly eastward along the Aleutians and toward Southwest Alaska. Even some high clouds ahead of this would affect how low temperatures drop. In any case, those still tending to gardens will want to prepare for the potential freeze/frost.
SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2).
Conditions are steadily improving across Southwest as we approach the weekend. The last of the shortwaves has moved off to the east, diminishing precipitation chances and reducing cloud cover. Flow across the Mainland becomes northerly today, advecting colder, arctic air into the region. When coupled with the lack of cloud cover, anticipate temperatures to drop to at or below freezing across much of the area overnight Friday into Saturday. Areas further inland, such as the Kuskokwim Valley and interior Bristol bay, will likely see temperatures in the upper 20's early Saturday morning. Coastal areas are expected to be quite a bit warmer in comparison, with lows in the mid-30's.
SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2).
A Bering low pushes off to the southeast by late this evening. Gale force winds will persist along the coastal waters surrounding the Central Aleutians until the system moves out. Additionally, areas of widespread small craft winds linger across the eastern Bering and waters along the AKPen through Friday night. Rain showers continue along the Eastern Aleutians, Southern AKPen and Pribilofs through this evening before beginning to fizzle out. Cold, northerly, arctic air advects ahead of a surface ridge building in the central Bering and flows over the AKPen, creating strong winds through the gaps and passes, with locally stronger gusts. Another low pressure system develops west of the Western Aleutians by Friday. Its front moves over the Western Aleutians early Friday afternoon, generating areas of heavy precipitation and areas of strong, gale force winds. The system occludes before reaching the Bering, however, there is still a possibility for brief areas of low end storm force gusts.
MARINE (Days 3 through 5/Saturday through Monday).
Gulf of Alaska . Lingering northwesterly high end gales through the Barren Islands and Sitkinak areas behind an eastern Gulf low diminish over the western Gulf by Sunday. Seas to 15 ft over the western Gulf, subsiding Sunday. A front moves across the Gulf through Monday. Southeasterly high end gales precede the front as it extends across the Gulf and along the Alaska Peninsula coast through Monday. Seas building to 15 ft east of Kodiak Island for Monday. The low weakens as it enters the Gulf for Monday.
Bering/Aleutians . A well developed western Aleutian low weakens as it moves along the Aleutians into the western Gulf by Monday. Predominantly high end gales with local areas of storm force winds with the wind-wrapped low, slowly diminishing through Monday. Seas to 20 ft on the Pacific side of the Aleutians and Alaska Peninsula through Monday.
LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday).
A cold snap is forecast for the weekend as a wave of low pressure rotating around the periphery of a polar low further to the north is able to dig southward and all the way into the Gulf on Saturday. Sub-freezing temperatures aloft will accompany the low's passage through the Alaska interior followed by weak ridging of high pressure over the Gulf and Southcentral. This should promote favorable conditions for strong radiational cooling during the overnight hours, and the end result will be freezing or near- freezing surface temperatures from Southcentral into Southwest early Sunday morning.
Meanwhile, an amplified low will be progressing eastward across the Aleutians with unsettled conditions ahead of and behind the low. Elevated winds gusting to gale force and showery conditions will impact the southern Bering, the Aleutian Chain, and the Alaska Peninsula throughout the day. By Monday, the amplified low will begin to weaken while overtaking the entirety of the Gulf. East to northeasterly barrier jet winds are forecast along the Gulf Coast with the Shelikof Strait likely to experience the highest winds. With low pressure expected to remain south and confined to the Aleutians and Gulf of Alaska, much of Southcentral and Southwest will experience drier conditions. However, there are some hints that a weak front will sag southward across Southcentral Monday into Tuesday, but any rain chances will likely be confined to areas that experience upslope flow over the higher terrain.
Further ahead, less certainty entails the Tuesday through Wednesday period. Latest numerical guidance is in loose agreement with the arrival of a strong North Pacific low overtaking the Western and Central Aleutians late Monday into Tuesday and expanding eastward to the Southwest coast by Wednesday morning. This will bring another round of enhanced winds, showers, and widespread low-level stratus next week.
AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . NONE. MARINE . Storm Warning: 119. Gale Warning: 120,130-132,138,139,173-178,351. FIRE WEATHER . NONE.
SYNOPSIS AND MODEL DISCUSSION . AS SOUTHCENTRAL ALASKA . SB SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . KM MARINE/LONG TERM . MK/BL
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