textproduct: Juneau

UPDATE

06z Aviation update. Moderate to heavy snow showers continue to be the primary threat and challenge from the Icy Strait Corridor (PAGS/PAOH/PAJN) south to Dixon Entrance. Any aviator attempting to navigate southeast Alaska should plan on periods of LIFR to IFR snow showers, with VFR in between. There is a decent signal that Juneau may hold onto more frequent snow showers early Tuesday morning. Northerly outflow winds will also continue to strengthen across the northern Panhandle, primarily impacting Lynn Canal and Glacier Bay. For folks flying the northern coast to/from PAYA, expect VFR to hold.

Snow showers will continue to plague the region Tuesday night into Wednesday creating a complex aviation forecast. Plan on periods of IFR from moderate to heavy snow showers.

PREV DISCUSSION......ISSUED AT 349 PM AKDT

SYNOPSIS...

Key Messages:

- Widespread convective showers continue into mid week, with chances of snow decreasing from north to south.

- Outflow conditions will continue to strengthen through the week and peaking on Wednesday. Outflow will bring colder, dryer weather for the northern half of the panhandle.

- Snow showers look to continue for the southern half of the panhandle through midweek.

SHORT TERM...Complicated pattern going forward, with a very slow moving, vertically stacked low in the eastern gulf bringing snow showers into areas from Icy Strait down the the southern panhandle. As such, very cold temperatures aloft and conditionally unstable profiles up to around 600 mb are present. As of now, showers are moving from the southwest towards the northeast, primarily focused on an area from Prince of Wales Island up to Kake and Petersburg. Furthermore, a band of convection has settled over the Juneau area, with the only thing lacking is moisture. Going forward into Tuesday, expecting to see this low pressure move southward, shifting the storm direction of these showers to be more moving northward rather than northeast. This is expected to keep stronger showers away from Sitka, Petersburg, and Wrangell, and increase the likelihood of shower development along the eastern side of Baranof Island, including Tenakee Springs and possibly Hoonah. As the low moves further south during the Tuesday timeframe, Icy Strait including Juneau will see increasing dry air aloft, limiting the amount of available moisture for showers.

LONG TERM...The main story for the mid to the end of week will continue to be northerly outflow with a chance of snow showers over the central to southern portions of SE AK. These showers will continue to be variable allowing the heaviest showers to bring moderate snow with reduced visibilities, and times of slightly increased winds. The next wave of moderate to heavy showers is most likely to move over the central and southern panhandle Wednesday and Thursday as a band of higher vorticity moves northward. Currently, highest accumulation looks to be over Prince of Wales Island with the most likely solution of 2 to 4 inches in 24 hours with a low chance of 20 to 40% chance of snow amounts near 6 to 8 inches. We will continue to monitor these chances. The upper level low over the gulf, along with the high pressure over the Bering Sea, will continue to allow for northwesterly flow to bring cold air over the panhandle. This will continue to slowly decrease temperatures as well as keep the precipitation type as snow. The far southern panhandle will still see times of rain or a rain/snow mix, but snow will be the most likely precipitation type.

Otherwise, winds will continue to become northerly across the inner channels with outflow winds building. All inner channel winds are anticipated to become northerly by Thursday. Strongest outflow winds will remain over Lynn Canal into Point Couverden, N Stephens Passage, and Icy Strait with strong breezes to near gales (22 to 33 kts) through the weekend. Times of gale force winds (34 to 40 kts) are also possible, most likely occurring Wednesday and Thursday over Lynn Canal. For land winds, Skagway is likely to see strong winds with a 50 to 60% chance of wind gusts near 40 mph on Wednesday.

This colder pattern looks to continue through the weekend into the start of next week as the high remains over the Bering Sea. This means that the next system that pushes into the panhandle will likely bring more snow to the area due to the colder temperatures in place. We will continue to monitor for when the next low pressure system may arrive allowing for this change in pattern.

AVIATION.../ through Tuesday afternoon / Broad scale low over the gulf persist through Tuesday staying quasi-stationary so onshore flow will keep showers activity ongoing. Better snow amounts for the coastal locations and then along the coast mountains which ride higher shower catchers. VFR conditions this evening, though should see stuff lower overnight so ceiling could lower below 3000ft. The southern half of the panhandle should see the worst of conditions.

MARINE... Outside (Gulf and Coastal Waters): Somewhat stagnant pattern for the outside waters, with a vertically stacked low drifting southward through the next 36 hours. For the NE gulf coast, expect to see a gradual increase in NE gap flow winds to a strong breeze out of interior passes, including out of disenchantment bay. A gradual decrease in westerly swell from north to south will lead to a decrease in wave heights from 12-15 ft to 7-9 ft.

Inside (Inner Channels): Again, somewhat stagnant pattern for the inside waters, with a similar story of a slow transition into northerly winds in Chatham Strait, Stephens Passage, and Frederick Sound. Main uncertainty with the short term is how fast the transition from SE winds to NE, particularly near Five Finger, and when it transitions to NE, will the winds also collapse down to a gentle breeze. Otherwise, high confidence on the fresh to strong breezes for Lynn Canal, down to the convergence point of Point Couverden, with strengthening slowly through Wednesday.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Weather Advisory until 4 PM AKDT Tuesday for AKZ321. Winter Weather Advisory until 4 AM AKDT Tuesday for AKZ325-328. Winter Weather Advisory until 10 PM AKDT this evening for AKZ326- 327-329. MARINE...Small Craft Advisory for PKZ012-013-022-053-641>644-651-661>664- 671.