textproduct: Juneau

UPDATE

/Update to aviation section to include 18z TAF Issuance/... Snow has proven heavier than anticipated across the northern half of SE AK, driven by a strong surge of moisture in the lower levels. Winter weather advisories are out for much of the Icy Strait Corridor and parts of the far northern panhandle. Snow will change over to rain during the afternoon hours for the Icy Strait Corridor, though it may linger longer in the far northern panhandle.

SYNOPSIS

- Weaker front moving through Thursday morning will bring snow to the norther half of the panhandle and rain for the south.

- Warming temperatures for the end of the work week. A system looks to bring moderate to heavy rain for Friday.

- Cooler temperatures with rain changing to snow showers over the weekend.

LONG TERM

A warm and moist airmass looks to move across Southeast Alaska through Friday as a strong low pressure system tracks north of the panhandle. Associated with this strong low is a particularly strong jet aloft, exceeding 130 knots, spreading over the northern panhandle. The resulting pattern will see height falls and pressure drops in the yukon, and pressure rises near the southern panhandle. Therefore, a predominantly southerly wind regime is in order for late this week into the weekend. Widespread moderate to heavy rain is expected across the region on Friday along with elevated snow levels. Rising snow levels combined with strong southerly flow looks to mix out any remaining cold air, transitioning areas in the northern panhandle to all rain.

Going into Friday night and Saturday, a surge of colder and moist air will slowly begin to drop snow levels and convert precipitation type back over to snow. The northern panhandle looks to see all snow by Saturday morning, with areas to the south following over the course of the day. Late in the weekend will see the aforementioned jet drop south, driven by the northerly, cold winds aloft. This will allow more cold air to move from north to south. Additionally, with continued onshore flow, snow remains in the forecast late in the weekend and into next week.

Forecast confidence in the overall synoptic pattern evolution is moderate to high, particularly regarding the transition to colder temperatures and a snowier regime by late Saturday and Sunday. Confidence in precipitation type transition from rain to snow is high. Main sources of uncertainty is in exact precipitation amounts, especially for Friday and Saturday. As rain transitions to snow, will need to pay attention to QPF trends particularly for the Central Inner Channels and Prince of Wales Island Saturday into Sunday.

AVIATION.../through 18z Friday/

A shortwave trough moving into the panhandle through the early morning is expected to continue precipitation and MVFR to IFR conditions for a majority of sites Thursday. The rain/snow line is currently sitting just below the Icy Strait Corridor, but is expected to continue to shift north as onshore flow continues to push showers into the panhandle through the day. Currently seeing periods of light to moderate rain showers for all sites to the south, wet and heavy snow reducing VIS to 1 to 2 SM along the Icy Strait Corridor, and more dry, light snow showers to the north. Widespread showers are expected to continue for the panhandle through the evening, with generally MVFR to IFR conditions continuing with between 2 to 4 SM of VIS and OVC CIGs AoB 3000 ft with potential for low scud around 700 ft. A stronger, more organized front is expected to push into the panhandle overnight into Friday morning, reaching the outer coast around 15z and moving inland by 18z. This will bring VIS and CIGs down to a more consistent MVFR, with periods of IFR possible as the main front moves overhead.

MARINE

Outside (Gulf and Coastal Waters): Not a lot of wind in the gulf this morning with the highest being an area of 25 kt SW winds S of 57N. There is a trough axis planted E to W across the gulf at around 57N latitude where winds north of it are out of the E while winds south are out of the SW. That feature is expected to move north through the day eventually leaving most of the gulf with S to SW winds leading into Thursday night. The next major system starts to move into the gulf on Friday with winds across the northern and Central gulf increasing to gale force by mid day Friday. Seas range from 6 to 9 ft with the highest seas over the south. Primary swell is from the W with a height of 5 to 7 ft and period of 10 sec. Not expecting much change in seas through the next 24 hours either. That changes into Friday as seas begin to increase into the 10 to 20 ft range due to the increasing winds from the next incoming front.

Inside (Inner Channels): The inner channels are mostly quiet with 20 kt or less of wind mainly from a S and W direction. Clarence Strait has somewhat higher winds to 25 kt from frontal winds that will mainly be this morning before diminishing. Otherwise mostly South and West winds of 20 kt or less expected in the inner channels through Thursday night before they start increasing into Friday afternoon as then next front approaches. Seas largely 4 ft or less through the period except for some higher seas near ocean entrances exposed to the west due to some swell getting into those areas.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Weather Advisory until 3 PM AKST this afternoon for AKZ319. Winter Weather Advisory until noon AKST today for AKZ320-325. MARINE...Small Craft Advisory for PKZ036-641-642-644-651-652-661>664-671- 672.