Marine Weather and Tide Forecast for Petersburg, AK

SYNOPSIS

Key Messages:

- Snow showers continue to taper off from north to south through Friday evening. Localized heavier showers and gusty winds are expected.

- Impactful snowfall event beginning on Saturday for portions of the northern and central panhandle. A Winter Storm Warning is in effect for Saturday for total snow accumulations of 6 to 10 inches. A winter storm watch has been issued for a follow up snow event for the central panhandle Sunday with an additional 6 to 12 inches possible.

- Potentially impactful snow to continue to shift northward through the panhandle Monday into Tuesday with a transition to rain likely for portions of the southern panhandle as another storm moves into the gulf.

SHORT TERM
Weak low pressure off the coast of Baranof Island and cold temperatures that pushed in from the north have kept ocean effect snow showers and cloud cover over the central areas today. The light scattered to numerous snow showers will continue to pass over the region Friday night with new accumulations of up to 2 inches. These widely scattered accumulations are separate from the next systems set to affect the area. Through Saturday morning, a low will track eastward across the central gulf while deepening. This will bring steady accumulating snow to the area with rates increasing through the afternoon.

As the low center tracks eastward through Saturday afternoon and evening, south to southwest wind will cause temperatures to warm over the southern outer coast with a mix or change to rain. Some areas near the low center could see gusts to around 35 mph and will need to monitor for potentially higher. Snow will then end on the NW side of the low, from Sitka to Juneau northward Saturday night. Winter storm warnings and advisories have been issued for Gustavus to POW and Hyder. Areas to the north (Yakutat, Haines, Skagway) are currently expected to see less than 2 inches on Saturday. For the Ketchikan and Metlakatla areas, 1-3 inches of accumulation is possible before they see mixing with rain Saturday afternoon.

Moisture will decrease overnight Saturday across the south, but then redevelop on Sunday as another system moves in. The rain/snow line will likely hover in vicinity of Sumner Strait Sunday into Monday with potential additional heavy snow for the Petersburg and Wrangell areas and lighter snow northward. A separate low pressure system looks to affect the region on Tuesday with potential for snow to push northward again.

LONG TERM
Winter continues to flex its muscles this weekend and into early next week with more snow and cold temperatures. An upper level trough over the interior will help to anchor high pressure at the surface and drive colder continental air into the northern inner channels. While the surface ridge does not look to be excessively strong (around 1040 mb), the important thing to note is the upper level support and overall staying power. This upper level pattern will also steer more storms and short wave features into the panhandle overall, being a classic setup for overrunning to bring ample snow to a majority of the panhandle. After the first influx of snow impacts the panhandle Saturday, there will be a brief lull and/or decrease in rates, particularly for the northern panhandle, before it ramps up again Sunday into Monday. The key question, particularly for Sunday into Monday, is how far south the arctic boundary stays entrenched.

There is relatively good model agreement on this boundary setting up in the vicinity of Sumner Strait by the start of the long range forecast period and hovering around that area to start the week.
Wavering of this rain snow line could lead to highly variable snow amounts as well as snow characteristic in terms of being light and fluffy or wet and otherwise harder to deal with. While communities north of Sumner Strait will likely see light and fluffy snow throughout this period, Petersburg and Wrangell as well as northern parts of Prince of Wales Island will be watched very closely in this regard. A winter storm watch has been issued for Petersburg and Wrangell as they remain in the cross hairs for the tail end of the first batch of snow mentioned in the short range discussion, and another surge of moisture Sunday afternoon into Monday.

South of Sumner Strait, a quick transition to a rain snow mix and rain is expected with very little to no snow expected at this time for Annette Island, Ketchikan, and southern Prince of Wales Island.
This will be looked at in greater detail and adjusted as necessary based upon how the forecast plays out with the arctic boundary on Saturday.

For the panhandle north of Sumner Strait, temperatures and dew points are expected to remain low enough to maintain snow throughout the period, and likely be lighter and more fluffy. While the heaviest snow rates are expected to impact the central panhandle, light to moderate snow will slide northward through the beginning of the week. For more information on any expected marine impacts in the forecast period, see the marine discussion below. Stay tuned for further forecast updates for this active pattern.

AVIATION
Snow showers across the panhandle are becoming fewer in number and intensity, and are mainly concentrated along the outer coast from Baranof Island southward this afternoon. Vis and ceilings with these showers continue to rapidly change flying conditions as they move through an area with VFR conditions one minute becoming IFR or even LIFR 15 min later before rebounding back to VFR or MVFR once the shower passes. Ceilings down to 2000 ft are also being encountered from Gustavus and Hoonah down to Angoon this afternoon due to weaker westerly flow over the gulf overrunning cold air outflow in the inner channels this afternoon producing a large area of cloud cover over the central and northern inner channels. Expect most areas in the south to become mostly VFR into tonight while the northern inner channels will likely keep ceilings around 2000 to 4000 ft through the night.
Into tonight another area of snow showers is expected to move in from Cape Fairweather southward that may bring more periods of MVFR or IFR conditions as more snow moves in.

Into tomorrow, a new weather system is moving in from the west that will start to spread snow over most of the area from Cape Fairweather southward Saturday morning. Expect ceilings to drop to 2500 to 1000 ft and vis to drop to 1 to 2 miles for many areas as snow starts Saturday morning and increasing in intensity through the day. Winds will not really be a factor until Saturday afternoon when some low level wind shear starts to show up over the southern panhandle and outer coast. This will be some directional and speed shear due to winds at 2000 ft coming out of the SW at 30 to 40 kt while sea level winds may still be SE at 15 kt or less.

MARINE
Outside (Gulf and Coastal Waters): Winds continue to weaken this afternoon across the Gulf and outside waters with observations across the area reporting moderate to fresh breezes. Sea state has also been on the downward trend with Gulf water buoys. This diminished winds and sea state is expected to increase though heading into tonight and tomorrow as the next low works north into the Gulf of Alaska. This low is expected to bring fresh to strong breezes to the Outer Coast along with a building sea state. Seas are expected to build up to 10-14 ft south of Cape Edgecumbe as this next low moves into the area. Farther north, seas are expected to be less significant. The swell direction is expected to remain out of the S-SW direction during this time. Another low is expected to move into the area Sunday into Monday bringing more active weather to the outside waters.

Inside (Inner Channels): Outflow conditions across the Inner Channels continues to weaken this afternoon as observations across the area show weakening winds. These winds are expected to diminish through the rest of the afternoon before starting to trend up again in response to an approaching low moving into the Gulf of Alaska.
Winds in the Inner Channels are expected to get up to fresh to strong breezes with this next system for Saturday into Sunday. But some pockets of near gales to gales could still be possible, especially through areas of narrow terrain. With an Arctic boundary expected to set up, parts of the Inner Channels will be out of the north while locations to the south of this boundary will be out of the south as this next system approaches. Another low is expected to move into the area for Sunday into Monday which will bring more active weather to the Inner Channels.

AJK WATCHES/WARNINGS/ADVISORIES
PUBLIC...Winter Storm Warning from 6 AM to 9 PM AKST Saturday for AKZ320>322.
Winter Weather Advisory from 6 AM to 6 PM AKST Saturday for AKZ323.
Winter Weather Advisory from 6 AM to 9 PM AKST Saturday for AKZ324-327-328.
Winter Storm Warning from 6 AM to 11 PM AKST Saturday for AKZ325- 326-329.
Winter Storm Watch from Sunday morning through Monday morning for AKZ326-329.
Winter Storm Warning from noon Saturday to noon AKST Sunday for AKZ331.
MARINE...Small Craft Advisory for PKZ031-033-034-641-642-661>663.