textproduct: Juneau

UPDATE

Update after 18z TAF issuance. Deep low in the eastern gulf has strong SW flow to the southern panhandle. Wind is a main hazard feature of this system. Ceilings are fairly widespread 1500 to 3000 feet in the Marginal category, while precip is adding some vis restrictions, most are above 3 miles. Also the potential for afternoon stronger convection primarily western Prince of Wales Island ( Cooler air aloft, warmer water below leading to conditional instability, then adding in orographic lift over terrain to assist vertical development. ) This may be strong enough for Thunder development, will be keeping an eye on situation.

Marine update: Outside (Gulf and Coastal Waters): Thursday morning observations are highlighting storm force conditions along our coast, with the highest winds focused from Cape Ommaney south toward Dixon. Given satellite wind passes, able to narrow down the 35 ft seas, likely aimed toward Baranof coast and northern Prince of Wales coast. Along the northern coast, buoy observations from 46082 and 46083 reported significant wave heights about 10 to 15 ft lower than forecasted, which was a direct result of a southerly shift in the storm force low; forecast was updated at 0800 Thursday to reflect this shift. However, one item of note was prominent WSW swell at 17 seconds, masked by the fresh seas generated from the strong low. Moving into early Friday morning wind and seas begin to diminish along our coast. Next system will be a low that will take a southeast transit along our coast Saturday night, bringing gale force northwest winds to the central gulf and seas increasing. Mariners wishing to transit from Cross Sound to Cape St. Elias will see winds less than 30 knots and seas less than 12 ft if they favor the coast.

Inside (Inner Channels): Observations around the inside this morning more or less agreed with yesterdays thoughts: N winds of moderate to fresh breezes in Lynn Canal, with conditions rapidly deteriorating as you move south from the Icy Strait Corridor. A few observations in Clarence Strait were reporting southwest gusts to 53 knots as of 0800 Thursday. Moving through Thursday afternoon high winds will continue to shift east into the Panhandle, driving strong gales with gusts to storm force for most of the central and southern passages. Stephens Passage looks particularly intense Thursday afternoon, with a few hours of storm force conditions starting near 1 to 2 pm Thursday afternoon. Moving through Thursday night, wind and seas begin to subside, bringing light winds through Saturday. An extended period of outflow conditions begins Sunday, with gale force conditions ebbing and flowing through the week.

PREV DISCUSSION...ISSUED AT 559 AM Feb 12

SYNOPSIS...

Key Messages:

- Numerous maritime storm warnings through Thursday over the eastern Gulf of Alaska and along the near shore waters of the outer coast from Sitka southward.

- Winter Storm Warnings and Winter Weather Advisories remain in effect for the northern inner channels for snow potential. Highest accumulations are expected on Haines Highway, including areas like Klukwan.

- Multiple High Wind Warnings and Wind Advisories remain in effect for the panhandle, with highest winds along and south of a line from Sitka to Kake.

- Increasing potential for thunderstorms Thursday afternoon for southern panhandle, highest likelihood near Prince of Wales Island and the surrounding areas.

- Weather pattern change begins on Friday, with showers diminishing in coverage through the day.

SHORT TERM... The storm force system over the eastern Gulf is rapidly approaching Baranof island as of the time of writing. An occluding front has been advancing through SE AK overnight, bringing widespread windy conditions for the central and southern panhandle, snow for the far northern panhandle, and rain for everyone else. While the system's initial front will depart the area through the morning hours, the landfalling low itself will bring with it a second wrap later in the day on Thursday, bringing about another round of rain and wind. Embedded along the eastern flank of the second wrap, a developing mesoscale low will bring with it an additional spike in winds for areas south of Angoon. By Thursday night, winds and precip will be on a downward trend, although chances of thunderstorms will present themselves for the southern outer coast and the vicinity of Prince of Wales Island. By Friday, lingering showers will be diminishing in coverage as the onshore flow fades away, and by late Friday into Saturday and cooler weather will be ushered in as northerly outflow conditions start to develop.

LONG TERM... Onshore flow will continue for the start of the long term period with a weakening low remaining in the northern Gulf for the end of the week. This onshore flow will continue to bring moisture into the area allowing for showers to continue. Most of these showers should remain on the lighter side but could potentially have some periods of moderate to heavy rain mixed in. Going into the weekend, high pressure builds over the Yukon and Interior Alaska before shifting to the south and east. This shift will strengthen the pressure gradient between Canada and the Panhandle. With this increasing gradient, winds out of gaps in terrain are expected to increase with outflow winds. Temperatures are also expected to start to decrease going into this weekend with a lot of locations expected to drop below freezing for the northern and central panhandle by Saturday morning.

With the dropping temperatures and continued onshore flow, some snow showers are likely to occur but would result in light snow accumulations at this time. Heading into Sunday, an area of low pressure is expected to form near Prince William Sound before moving into our area. This low will bring an increase in upper level dynamics as well as a more organized area of snow. This would be the first return of snow to most of the panhandle since we moved out of the cold and snowy pattern in January. Right now, accumulations for this system on Sunday look to be around a couple inches for most places. But those locations that are at elevation could of course see higher snow totals. Going into the middle to end of next week, we look to continue to the cold trend with near normal to below normal precipitation.

AVIATION.../through 12z Friday/ Predominate MVFR to VFR flight conditions for the panhandle this morning with CIGS AoB 4000ft and visbys 3 to P6SM as the second of two systems from previous days pushes across SEAK. Main aviation hazard through Thursday will be strong surface winds and SE- ly LLWS for southern and central Panhandle TAF sites increasing after, with maxima through Thursday morning around 40 to 60 kts between 1000 to 2000ft for PASI, PAKW, PAKT, decreasing further moving northward and inland around 30 kts near Juneau. Overall flight conditions will remain similar to yesterday, predominate MVFR to VFR with periods of IFR visbys within heavier showers moving on-shore, CIGS remain AoB 5000ft. Post-front, added PROB30 for potential thunderstorm development for PAKW for Thursday afternoon.

MARINE... A dangerous storm force low racing into SE AK will continue to bring storm force conditions to the central and southern coast and widespread gale force conditions in the inside.

Outside (Gulf and Coastal waters): As of early Thursday morning, storm force winds and significantly elevated seas are present for areas south of Sitka Sound. Accompanying them are frequent gusts of violent storm force to hurricane force. These winds are generating seas of up to 35 ft, with the higher seas in the more southerly outer coastal areas.

Right now, current forecast consensus is that areas south of Lisianski Inlet will be hardest hit. By late Thursday night, seas will be on a downward trend, and Friday will dawn with seas of between 9-14 ft, with seas of 8-11 ft by late Friday night.

Inside (Inner Channels): Winds continue to strengthen as a storm force low approaches northern Baranof Island. Winds will continue to ramp up Thursday morning with gale force conditions across many inner passages, and storm force conditions for some of the southern inner channels. One exception will be Lynn Canal, where we will hold on to northerly winds of moderate to fresh breezes for areas north of Vanderbilt Reef. We approach with caution as areas south of Pt. Retreat and Douglas are likely to maintain easterly near- gale to to gale force conditions. Wind and seas subside Friday morning bringing better conditions until outflow begins strengthening on Sunday.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Weather Advisory until 3 PM AKST this afternoon for AKZ318. Winter Storm Warning until 3 PM AKST this afternoon for AKZ319. Wind Advisory until 6 PM AKST this evening for AKZ320>322-324- 325. High Wind Warning until 6 PM AKST this evening for AKZ323- 326>330-332. MARINE...Storm Warning for PKZ033-035-036-641-642-661>663. Gale Warning for PKZ013-021-022-031-032-034-643-644-664. Small Craft Advisory for PKZ011-053-651-652-671-672.