Marine Forecasts

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7 Day Forecast for Marine Location Near Seldovia city, AK

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Area Discussion for -

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FXAK68 PAFC 051240 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 440 AM AKDT Wed Aug 5 2020

ANALYSIS AND UPPER LEVELS.

A vertically stacked low positioned over the southeastern Gulf continues to fill and weaken as it drifts toward the Alaska Peninsula. Radar returns from the Middleton Island radar show an increase in shower activity over the northern Gulf in association with an upper-level trough extending from the low. Over Southwest Alaska, a transient upper-level ridge stretching from the Kuskokwim Valley south to Bristol Bay is resulting in drier and more stable airmass with only an area of low stratus and fog settling along the Bristol Bay coast overnight. An upper- level wave continues to drop across Southcentral overnight, caught up in the northeasterly flow between the ridge and the low over the Gulf. This is the feature responsible for the scattered showers and isolated thunderstorms across parts of the Susitna Valley and Copper River Basin this afternoon and evening.

Farther west, a 990 mb low is situated approximately 200 nm north of Adak. This system continues to deepen as it swings a warm front from the Pribilofs to the eastern Aleutians and a trailing cold front across the western Aleutians, bringing widespread clouds, gusty winds (including areas of gales), and rain to the region. The upper-level dynamics are favorable for further strengthening as the surface feature sits in the left exit region of a 130 kt jet streak. This system is still on track to enter the eastern Bering by late Wednesday with its front pushing onshore along the west coast.

MODEL DISCUSSION.

Models are in very good agreement regarding the departure of the Gulf low to the southeast and strength and movement of the Bering low as it tracks to the Southwest Alaska coast. There are some minor discrepancies in the track of the upper-level trough as it moves into the northern Gulf on Friday. However, any noted differences have little impact on the expected sensible weather. Given this, the morning forecast package will continue to trend towards the NAM/GFS solutions with the use of hi-res models for local effects.

AVIATION. PANC . VFR conditions will persist through Thursday morning. Southeasterly winds will develop around 00z and are expected to persist through early Thursday morning. Gusts of 25 to 30 kts are possible from mid-afternoon through late evening Wednesday. Shower activity in the vicinity of the terminal is also possible this afternoon and evening, but is expected to remain mainly over the Chugach Mountains east of the airport.

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

An upper level trough extending up into eastern Southcentral from a large low over the eastern Gulf will bring numerous showers to the southeastern Copper River Basin and eastern Prince William Sound regions today. Elsewhere, the thermal trough will strengthen a bit from Tuesday as a weak upper ridge moves into western portions of Southcentral. Surface heating in combination with unstable air will lead to another round of diurnal showers and thunderstorms. As was the case yesterday, convection will initiate along the mountains. However, today they will track in the opposite direction as southerly winds develop this afternoon.

The continued instability will also bring locally strong and gusty gap winds to Turnagain Arm/Anchorage and the Knik River Valley into Palmer late this afternoon through evening as a surface ridge builds along the north Gulf coast. A front associated with a strong vertically stacked low currently residing in the Bering will then make its way into the Gulf tonight, leading to increasing low level southeasterly flow as well as strengthening of the coastal surface ridge and pressure gradients. As a result, strong and gusty winds are again expected to push through Turnagain Arm and spill into Anchorage (mainly the upper hillside) and the Matanuska Valley on Thursday.

The details of the wind forecast in the Anchorage area are a bit tricky. As the front approaches Southcentral, pressure gradients between Anchorage and Homer favor the Turnagain wind bending southward and staying out of Anchorage. This also usually results in a diminishing of winds along the Anchorage hillside. However, surface-based instability and a well-mixed boundary layer along with the aforementioned increase in low level flow (at mountain top level) will favor some winds mixing down to the surface during the afternoon hours. In particular, this seems like a scenario where Eagle River and the S Curves along the Glenn Highway may see some gusty winds.

This frontal system will bring moderate to heavy rainfall to Kodiak Island tonight then to the Eastern Kenai Peninsula and Prince William Sound areas on Thursday. Southeasterly flow will also enhance rainfall on the west side of Cook Inlet and the western Susitna Valley (near the Alaska Range). The remainder of Southcentral will experience downslope flow and will thus remain mostly dry, with just a chance of passing light showers.

The storm will weaken over the region on Friday. With weakening winds (and downslope flow) will transition to a showery pattern as the upper trough sets up shop over the Gulf and Southcentral.

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

Rainfall potential will rapidly increase over the next 24 hours. For this afternoon and evening, a few thunderstorms may develop along the Alaska Range from Iliamna north, but given the lack of thunderstorm development the last two days, which featured sufficient instability but a lack of appreciable lapse rates, hopes for today are fading fast. Incoming high cloud cover from the approaching front won't help matters either.

The real story will be a deepening low moving towards the eastern Bering Sea, sending a front ashore over the next 24 hours. As the low deepens, surface convergence along the front and ascent aloft will combine with increasing moisture though the column to foster widespread rainfall, some of which will be of decent intensity at times. Also, with the strengthening front, a tightening pressure gradient will allow for some gusty winds to develop, especially near coastal areas. The steady rainfall should reach the coast by late this afternoon/early evening . reaching the far interior locations by Thursday morning.

Then for Thursday afternoon into Friday, the low slowly fills and weakens as it slides across the Alaska Peninsula (AKPEN) into the Gulf. However, cyclonic flow on the backside of the low will be accompanied by disturbances rotating around the parent low . helping to maintain at least scattered (if not numerous) showers through the period.

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

The proverbial "calm before the storm" best sums up the short term weather for the eastern 2/3rds of the Bering and Aleutians, as a deepening low over the west central Bering will trek eastward while deepening, reaching the Bristol Bay region by Thursday afternoon, before sliding off to the southeast into the Gulf for Friday. The associated front is already approaching Dutch Harbor, and it'll reach the coast of southwest Alaska and the AKPEN by late this afternoon. Preceding its arrival, rainfall will be widespread, and at times somewhat intense rainfall given a semi- tropical connection.

The real story will be the the winds and waves for the eastern Aleutian and peninsula coastal waters. As the low deepens, dry advection behind the front will allow for rapid pressure rises. Cold advection aloft, aided by modest tropospheric anomalies (as seen on the 1.5 mb PV anomaly forecasts) reaching 400 mb will help augment downward momentum transfer to some extent.

The net result will be sustained gales developing east of Adak across the coastal waters and southern Bering Sea. Here, seas will build into the 10 to 15 feet range north of the chain, and 15 to 20 feet south of it (due to a longer fetch length). For the western bering and Aleutians, short-wave ridging will build behind the storm, allowing for drying conditions to commence.

MARINE (Days 3 through 5: Friday through Sunday).

Bering Sea/Aleutians

A Southwest Alaska low moves into the Gulf of Alaska by Sat. Confidence is good for rear flank small craft winds and waves over the Eastern Bering and Bristol Bay diminishing Sat. A low exiting Anadyr moves across the Bering through Sun. Although model tracks are mixed, confidence is good for Westerly small craft winds to move across the Bering and diminish Sun. A North Pacific low approaches the Western Aleutians and Bering for Sun. Confidence is good for Southerly small craft winds with local gales over the Western Aleutians through Sun.

Gulf of Alaska

A low and its front to the East of Kodiak Island tracks into the Northeastern Gulf for Sun. With consistent model tracking, confidence is good for Easterly small craft winds and waves through Sun with local gales near capes ahead of the front for coastal zones diminishing Sat, and widespread Westerly small craft winds through Sun with local gales diminishing Sat to move across the Gulf.

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday) .

A fairly active and progressive longwave pattern looks to setup this weekend as a series of systems move eastward from the Bering Sea/Aleutians into the middle of next week. The first of these will be a developing low diving from Siberia into the Gulf, bringing cloudcover to much of the South Mainland and rain primarily to the Gulf Coast. The next low will quickly follow the Siberian Low, and will be the first in a series of lows moving into the Bering from Kamchatka. This pattern will allow for generally cloudy, cool conditions for much of the area, with storminess for the Bering Sea and Gulf of Alaska.

AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . NONE. MARINE . Gale Warning 155, 165, 170-177. FIRE WEATHER . NONE.



SYNOPSIS AND MODEL DISCUSSION . TM SOUTHCENTRAL ALASKA . SEB/KM SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . PD MARINE/LONG TERM . MK/DK

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Weather Reporting Stations

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Stations	Dist	Age	Wind	Air Temp	Water Temp	Waves	Pressure	DewPt
OVIA2 - 9455500 - Seldovia, AK	1 mi	59 min			52°F		1005.2 hPa
FILA2 - Flat Island Light, AK	17 mi	59 min	S 2.9 G 6	55°F			1005.7 hPa	49°F
HMSA2	19 mi	37 min	ENE 8 G 11	53°F			1003 hPa	47°F
AMAA2 - East Amatuli Light, AK	39 mi	119 min	WSW 14 G 17	56°F			1006 hPa	54°F

Wind History for Nikiski, AK

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Airport Reports

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Airport	Dist	Age	Wind kt	Visibility	Sky/Weather	Temp	DewPt	Humidity	Pressure
Seldovia, Seldovia Airport, AK	1 mi	36 min	N 0	mi	Fair	47°F	45°F	93%	1005.6 hPa
Homer, Homer Airport, AK	18 mi	36 min	NE 4	10.00 mi	Fair	53°F	48°F	86%	1005.7 hPa

Link to 5 minute data for PAHO

Wind History from AHO (wind in knots)

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Tide / Current Tables for Port Chatham, Cook Inlet, Alaska

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Tide / Current Tables for Homer, Kachemak Bay, Cook Inlet, 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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