textproduct: Juneau

UPDATE

18z Aviation TAF update As of 9 AM AKST Wednesday, conditions are mostly VFR to MVFR across the Panhandle, with CIGS AoB 4000 ft. The northern coast is currently seeing the worst conditions, with PAYA reporting LIFR VSBY and CIGS from +SN and VV005. This threat will continue to shift east and south through the next 12 hours with Pelican just starting to see SN; simply put, conditions will deteriorate through Wednesday afternoon as colder air moves. However, the complexity today will be the nature of snow showers, with MVFR to VFR conditions rapidly dropping down to IFR from +SN from periods of heavier showers. Moving through Thursday conditions improve slowly from north to south as outflow begins to dominate the Panhandle, bringing in cold and dry arctic air.

Touching on LLWS, expecting some chop from a westerly band of stronger winds near 2500 ft, likely near 35 to 45 knots, diminishing a bit as you drop below 2000 ft. Mainly impacting coastal TAF sites from PASI south toward PAKW.

PREV DISCUSSION......ISSUED AT 827 AM AKST WED

UPDATE...Heavy snow showers have started up at Yakutat this morning and after just a few hours we got a spotter report of 4 to 5 inches of new snow accumulation with moderate snow falling. Decided to issue a winter storm warning for Yakutat as satellite shows more heavy snow showers incoming for the NE Gulf Coast through at least the afternoon hours. Additional snow accumulation of around 4 to 6 inches, but if heavy showers continue to train over them Yakutat could receive more than that.

SYNOPSIS...

Key Messages:

- A low in the northern gulf will keep persistent snow showers spreading across the panhandle through Wednesday evening. Winter weather advisories remain in effect for Skagway, Juneau, Elfin Cove, Sitka, and Prince of Wales Island. - Outflow conditions return on Thursday morning, with increasing northerly winds, decreasing temperatures, and freezing spray expected within the northern panhandle inner channels through the end of the week.

SHORT TERM...Minor changes have been made to the forecast overnight, with the main ones being to slightly increase the outflow winds up north going into Thursday. A low in the northern gulf is directing moisture into the panhandle Wednesday, causing widespread showers to move through the panhandle. Temperatures will be trending downward through the day, but at the moment, much of the northern panhandle is cold enough that precipitation is all snow while the rest of the panhandle is still seeing rain. As the day goes on, below freezing temperatures will steadily creep south until the entire panhandle is seeing snow by later Wednesday night. At this point, low temperatures will be in the teens to single digits up north and in the 20s in the south. Higher elevation areas on mountains and ridge lines oriented NW to SE are still the favored area for heavier snow falls, with winter weather advisories still out for Elfin Cove, Pelican, Juneau, Skagway, Sitka, and Prince of Wales Island for snow rates in the 4 to 6 inch per 12 hour range. Due to the nature of showers, precipitation could be heavy at times and light/nonexistent at other times. Various localized areas could see a 20 to 30 percent chance of seeing snow totals that end up a few inches higher or lower than what is currently advertised. Since temperatures will be actively dropping below freezing through the day, snow will also generally be more wet and dense, which may restrict visibility and make travel more dangerous.

Gale force winds with storm force gusts are expected through the gulf with this system, with sustained winds up to 30 kts and pockets of gale force gusts expected through Cross Sound, Lynn Canal, and near Five Finger Lighthouse. Through the later afternoon as the onshore flow begins to calm down, strong outflow will begin to develop through the northern panhandle, strengthening overnight. This will largely switch wind directions from southerly to northerly, but the strongest outflow winds aren't expected to make it all the way down the channels. The northern channels and interior passes along the NE gulf coast will see high end gale force winds develop with strong gale force gusts overnight and last through early Thursday morning. This outflow will limit potential for showers to make it into the northern panhandle, so showers will steadily shift southward through the night.

LONG TERM.../Thursday through Sunday/... Convective snow showers continue into Thursday with cold air advection streaming across southeast AK, with a vertically stacked low and unseasonably cold temps aloft. However, northerly outflow will filter in drier continental air into the northern panhandle by Thursday afternoon behind the low passing southeast over the panhandle, effectively shutting off the snow from the Icy Strait corridor north. Showers will diminish significantly across the rest of the panhandle as well. An additional 1-3 inches of snow possible from Icy Strait south, with heavier amounts expected across near Port Alexander and Prince of Wales Island. Snow will develop back into the region on Friday with onshore flow, but lack of any significant forcing will keep fairly scattered and light.

With the northerly outflow strengthening and much below normal 850 temps aloft, expecting cold temps across southeast AK for the end of the week. Expect highs in the teens and lower 20s north to upper 20s and 30s central and south. Nighttime temps will dip down into the single digits to lower teens north to upper teens and 20s south. Below zero temps are possible along the northern highways, esp Thursday night, and there is the potential they reach Cold Weather Advisory criteria.

For the weekend, general model trend is for a frontal boundary straddling over the central/southern panhandle with ridging to the south and upper low to the north and a steady upper-level jet overhead. Multiple waves and upticks in moisture will pass along the boundary and through the panhandle, bringing more snow. Preliminary forecast is showing light to moderate snow along the Icy Strait corridor and Juneau with 4-6 inches possible, with heavier amounts up to 8+ inches possible south along the coast and over central/southern panhandle. Warmer air and rising snow levels could bring a rain/snow mix or all rain that would eat into snow total across the south. The drier air north of the boundary will limit the potential for significant accumulations for Yakutat and especially Skagway and Haines. Temperatures moderate a bit over the weekend as the arctic air retreats and the northerly outflow weakens.

AVIATION.../through 12z Wednesday/... Variable flight conditions ongoing this morning ranging from IFR to VFR as a low in the N Gulf sends rounds of showers across the panhandle. Tough aviation forecast as a wide variety of ceilings and visibilities will continue through the day as precipitation becomes more showery in nature, some areas improving to up to VFR conditions while other areas could drop down to IFR/LIFR visbys and CIGS during hit or miss heavier snow showers. Southern portions of SE AK will see showers start as rain before transitioning to snow through the afternoon into evening. Within VFR conditions, CIGS should generally remain AoB 5000 to 7000ft through the period. Winds across the N panhandle will increase through Wednesday afternoon due to increasing N/S pressure gradient with strongest sustained winds around 15 to 25kts with gusts up to 40 kts at Skagway. No significant LLWS concerns through the period, LLWS is likely along the central and southern coast TAF sites with westerly winds near 30 kts at 2000 ft beginning 15 to 18z at Sitka, Ketchikan, and Klawock, continuing through Wednesday evening. Lastly, with incoming showers, expecting low-end potential for isolated convective showers along the coast of Baranof southward to Prince of Wales this afternoon and tonight as low moves eastward.

MARINE... Outside (Gulf and Coastal Waters): A low in the northern gulf is directing winds and moisture into the panhandle through the central gulf through Wednesday. Expecting westerly gale force sustained winds with storm force gusts to persist through the outer gulf waters, staying elevated with the help of gaping winds through the Kenai in the western gulf. The outer gulf coast of the panhandle from Baranof Island down to Prince of Wales Island will see these strong winds licking up against the shore through the entirety of Wednesday, diminishing and shifting slightly more south with the upcoming outflow through Thursday morning. Highest wave heights up to 28 ft will follow the strongest winds in the central gulf, with 12 to 16 ft waves reaching the outer coast of the panhandle. Expecting 20 to 25 ft westerly swell with the strongest waves, at a period of between 12 to 14 seconds.

Inside (Inner Channels): The system currently directing winds into the panhandle will continue to bring widespread fresh to strong southwesterly breezes through the inner channels through the majority of Wednesday. Localized areas such as Lynn Canal, Cross Sound, near Point Couverden, and Near Five Finger Lighthouse are expected to see the higher end of these winds, with gusts reaching gale force. Through Wednesday evening, these southerly winds will start to be pushed back by building outflow in the northern panhandle, sending strong to gale force northerly sustained winds down through Lynn Canal and rounding Point Couverden. The rest of the channels will eventually switch northerly and pick up to fresh to strong breezes through Icy Strait, Stephens Passage, and Northern Chatham Strait. The strongest winds are not expected to make it all the way through the channels before outflow winds subside into Friday. Areas of the strongest winds will see wave heights up to 6 to 8 ft, while the rest of the channels impacted by the outflow winds should see up to 4 to 5 ft.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Storm Warning until 9 PM AKST this evening for AKZ317. Winter Weather Advisory until 9 PM AKST this evening for AKZ318. Winter Weather Advisory until 6 AM AKST Thursday for AKZ322. Winter Weather Advisory from 6 PM this evening to 4 PM AKST Thursday for AKZ323-328. Winter Weather Advisory until 6 AM AKST Thursday for AKZ325. MARINE...Gale Warning for PKZ012-013-053-641>643-651-661>664-671-672. Small Craft Advisory for PKZ011-021-022-031-033>036-644-652.