Marine Forecasts

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7 Day Forecast for Marine Location Near Sand Point, AK

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Area Discussion for -

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FXAK68 PAFC 200049 AFDAFC

Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 449 PM AKDT Sun Sep 19 2021

ANALYSIS AND UPPER LEVELS.

A large area of low pressure currently centered south of the Shumagin Islands is causing gusty winds across much of the Bering, AKPEN, and Eastern Aleutians. Rain is also occurring on the northern fringe of the precipitation shield in Sand Point. This low is expected to move into the Gulf, leading to numerous impacts across Southcentral. More on that below.

An expansive area of high pressure caused one of, if not the coldest morning of the fall season so far as clear skies extend all across southern mainland Alaska from the Canada border all the way to Bristol Bay. This has allowed for optimal radiational cooling. Sub-freezing lows were prevalent across nearly all of southern mainland Alaska this morning. A secondary area of high pressure envelops all of the western and central Bering and Aleutians.

In the upper levels, the low south of the Shumagin Islands is vertically stacked. The positively tilted trough with a 140 kt jet streak rounding its southeastern side is helping to gradually tilt the trough more negatively with time. A polar low is centered near Utqiagvik, driving an unseasonably cold air mass southward towards Southwest Alaska. The leading edge of this polar air mass is moving across the Yukon Delta.

MODEL DISCUSSION.

A very active weather pattern begins across Southcentral this upcoming week. On the large scale, the models are in excellent agreement through Tuesday afternoon. Unfortunately, with strong storms that involve winter precipitation, even small differences in the models can make for large differences in the forecast. There is high confidence that the focus of the lion's share of the precipitation with this storm will focus through Thompson Pass and the Copper River Basin. Given it is VERY early in the year to be talking low-elevation winter weather for most areas, by far the biggest point of uncertainty is timing when and how low in elevation the snow level gets Monday night into Tuesday with the incoming unseasonably cold air mass. As usual for September, warm surface temperatures initially will melt the first flakes as they reach the ground, but heavy precipitation intensity and a progressively cooling air mass will allow snow to last well into the day on Tuesday, despite more than 12 hours of September sun. If there is a changeover back to rain, or if not, snowmelt Tuesday afternoon both will also play a role and add significant uncertainty to snowfall amounts across the aforementioned areas. Forecast confidence is high that there will be significant precipitation across the area, and the cold air mass will drive temperatures area-wide well below seasonal normals. Confidence is much lower on precipitation type, and even lower still for accumulations, given surface temperatures and solar heating will play a major role in what those final amounts will be.

While much of the Cook Inlet region will be spared from the snow, though there is a decent chance of some minor accumulations at higher elevations on the Hillside and around Eagle River, the driving cold air mass will also result in gusty winds for much of the region. For Seward and Whittier, gusts will be strong Tuesday morning, potentially exceeding 50 mph. There is some uncertainty on how strong the highest gusts will be.

Looking ahead, there is very good model agreement that another low moves into the Gulf Thursday morning, and surprisingly great agreement on a third low moving in Saturday night. Both of these carry similar uncertainties with cold air and track, and both appear likely to produce additional snowfall accumulations somewhere over Southcentral, so stay tuned!

AVIATION. PANC . VFR conditions and light winds will persist. The predominant wind will be southeasterly this evening, but are not expected to become gusty. A strong cold front approaches during the day Monday, which could cause some VFR very light rain. Gusty northwesterly winds will develop late Monday afternoon or evening.

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Tonight through Wed afternoon) .

Mostly clear skies are expected across much of Southcentral tonight as the area remains under weak upper level ridging aloft. Temperatures are expected to be a bit warmer tonight due to slightly warmer 850 mb temperatures compared to last night. Most areas are expected to fall into the mid to upper 30s with some areas dropping down to around freezing especially in the Copper River Basin. Also, there is expected to be some packing of the isobars against the Chugach this evening as a coastal ridge develops out ahead of a storm system in the North Pacific south of Sand Point currently. As a result, a Turnagain Arm wind is expected to develop through this evening with the core (gusty winds) remaining out over the Arm and not coming into West Anchorage. At best, expecting a general 5-10 mph southeasterly winds this evening across West Anchorage.

Next, an early season winter storm (technically we are still in summer)remains on track to affect the Copper River Basin Monday through Tuesday night. A complex setup is expected to occur with this system. Looking aloft, a much stronger Arctic trough moving southward from the Seward Peninsula will supply the cold air to this system. The storm moving up from the south will supply the moisture needed. As a result, the two of these are expected to phase together right over the Copper River Basin. Therefore, expect rain to start out for basically everywhere Monday as the cold air won't yet be in place. As colder air gets drawn into the system Monday evening, expect rain changing to snow across the higher elevations first such as Eureka and Thompson Pass somewhere in the Monday evening timeframe 7-9 PM. As the cold air gets deeper, expect low elevations to change to all snow around to after midnight for places such as Gulkana, along the Glenn and Richardson Highways. The changeover may be delayed a bit longer for Chitina to McCarthy along the Edgerton Highway due to them being lower in elevation, thus longer for the cold air to seep in. A general 5-8 inches of snow is expected across the area Monday evening through Tuesday with 1 to 3 inches for Chitina to McCarthy and 8 to 12 inches for Thompson Pass. See Winter Weather Advisory that was issued for the Copper Basin more info. Across Southcentral, expecting mostly rain showers with any snow expected to occur across the Chugach Mountains and perhaps the Anchorage Hillside Monday evening into Tuesday. Any snow accumulation is expected to be none to minimal.

Wind will be another big factor with this system as cold air advection Monday night through Tuesday dives southward. As a result, expecting strong outflow winds through areas such as the Barren Islands, Seward, and Whittier as the cold air moves in. Gusts may reach as high as 50 mph for Whittier and Seward Monday night through Tuesday, especially Tuesday morning. The Anchorage Bowl itself will also be gusty with winds gusting up to 35 mph, especially on the west side of town. Thompson Pass is also expected to have sustained winds of 20-25 mph with gusts up to 35 mph.

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: This afternoon through Wednesday) .

A cold front will move through the area tonight and tomorrow bringing colder air and areas of light rain briefly changing over to snow by tomorrow morning. The area with the best chance of seeing light snow will be over the Middle Kuskokwim Valley early tomorrow morning. However, any snow will be brief and no accumulations expected. Behind the cold front most of the area will be cloud free with the exception of coastal areas of the Kuskokwim Delta. Expect temperatures below normal Monday afternoon in the mid to upper 40s and a chilly Tuesday morning with lows in the 20s across Bristol Bay and the Middle Kuskokwim Valley with upper 20s to 30s in the Y-K Delta area as some clouds will moderate low temperatures. High pressure will dominate the area Tuesday before an area of low pressure approaches the Y-K Delta with a chance of rain on Wednesday. Otherwise Bristol Bay and the Middle Kuskokwim Valley will see mostly sunny skies Tuesday and early Wednesday before clouds begin to increase by Wednesday afternoon.

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: This afternoon through Wednesday) .

Low pressure south of the AKPEN will move east into the Gulf through tomorrow morning with a ridge of high pressure settling over the Bering and Aleutians through Tuesday. Periods of Gale force winds from the north are expected south of the AKPEN through Tuesday morning as the low departs and cold air advection increases the winds through the Gaps. Another North Pacific low will move towards the central Aleutians on Tuesday with Gales expected on the Pacific side and spreading to the southern Bering by Tuesday afternoon and evening. This low will track south of the Aleutians with Gales moving into the eastern Aleutians and south of the AKPEN on Wednesday. Rain is also expected with this system but nothing significant.

MARINE (Days 3 through 5/ Wednesday through Friday).

High pressure across the northern half of the Bering spreads generally light winds over the region. A well-developed low south of the Aleutians spreads gusty winds less than gale force across the southern Bering. Widespread high-end gales wrap the low as it moves into the Gulf of Alaska by Friday. Seas to 18 ft along the Aleutians and Alaska Peninsula, subsiding Thursday. This low continues to the North Gulf Coast through Friday. High-end gales ahead of the low with areas of storm force winds near the capes along the North Gulf Coast down to Kodiak Island, dissipating Friday. Seas to 16 ft spread across the Gulf through Friday.

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

Deterministic and ensemble forecast models are in excellent agreement through the long term due to well defined and strong upper level features. A strong upper level jet ranging from 120 to 140 kts will extend a high amplitude trough from the Kamchatka Peninsula south to 40N and north to Southeast Alaska. An additional polar jetstreak is expected from the Gulf of Anadyr to the AKPen between 70 and 90 kts. With the jetstreak extending from the north Pacific to Southeast Alaska, a strong upper low is expected to develop in the left exit region and move into Southcentral Alaska Thursday through Saturday. Deterministic models have the surface low center somewhere in the vicinity of Prince William Sound Friday night, which will make for a difficult precipitation type forecast throughout Southcentral. Cold air aloft is expected to wrap in on the backside of the low, but seasonally high sea surface temperatures will likely yield rain at sea level with snow likely over the mountains.

Out west the weather will be a bit quieter with brisk northerly winds likely from Southwest to the AKPen and fairly quiet conditions for the central Bering. Over the western Bering storms are likely to track south from the Kamchatka Peninsula, over the western Aleutians, and into the north Pacific.

AFC WATCHES/WARNINGS/ADVISORIES. PUBLIC . Winter Weather Advisory 141. MARINE . Gale 119 130 131 132 138 150 155. FIRE WEATHER . NONE.

SYNOPSIS AND MODEL DISCUSSION . JPW SOUTHCENTRAL ALASKA . MV SOUTHWEST ALASKA/BERING SEA/ALEUTIANS . RC MARINE/LONG TERM . AF/CJ

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Weather Reporting Stations

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Stations	Dist	Age	Wind	Air Temp	Water Temp	Waves	Pressure	DewPt
SNDA2 - 9459450 - Sand Point, AK	18 mi	43 min					999.5 hPa
KGCA2 - 9459881 - King Cove, AK	97 mi	43 min	N 25 G 32	50°F	51°F		1000.7 hPa

Wind History for Sand Point, AK

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NW17 G24

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NW20

2 days ago

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Airport Reports

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Airport	Dist	Age	Wind kt	Visibility	Sky/Weather	Temp	DewPt	Humidity	Pressure
Sand Point, AK	19 mi	65 min	N 7	10.00 mi	Fair	51°F	39°F	64%	999.4 hPa

Link to 5 minute data for PASD

Wind History from ASD (wind in knots)

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