textproduct: Juneau

UPDATE...Update to include 06Z TAF issuance

The strong low pressure continues to lift north along the gulf coast and is expected to push onshore north of Sitka overnight with the attendant front lifting north through the panhandle. Drier, easterly flow has delayed the start of the heavier snow for the northern panhandle. The GOES snowfall rate product has the heaviest snow south of the Icy Strait Corridor slowly creeping north. Have lowered storm total snow accumulations down to 4 to 8 inches for the Winter Storm Warnings. Warmer air south of the front has switched snow over to rain this evening or will by early morning. Strongest winds have pushed east of POW. Gusty winds still possible for Ketchikan and Annette Island for the next few hours.

SYNOPSIS

Key Messages:

- A strong area of low pressure will move up from the northern Pacific, strengthening off the outer coastal areas of southeast Alaska through Monday.

- Winter Storm Warnings and Winter Weather Advisories are in effect through Monday, with highest accumulations expected along the Icy Strait Corridor and Hyder.

- Periods of snow will continue through most of next week as a cold airmass wrapping around a broad low stays over the eastern Gulf of Alaska keeping a pattern supportive of bands of heavier snow showers eastward across the Alaska Panhandle Tuesday through late next week.

LONG TERM

/ Wednesday through Friday/ Simple message: Onshore flow drives snow showers for the Panhandle Wed into the weekend, with varying snow amounts and potential for training snow showers. Likely a rain/snow mix for coastal locations.

By Wednesday a longwave trough positioned over the Gulf of Alaska will mature and stagnate, being reinforced by pulses of shortwaves sliding south from western AK. Cold air will continue to rotate around the backside of the parent system over the Gulf, with temperatures at 850mb holding near -10C for most of the region through the remainder of the week. At the surface, the dynamics aloft will continue to feed a surface low in the northern gulf, driving onshore flow across the region. Keeping things simple here, we will see continued snow showers across the Panhandle as cold air flows over the relatively warm Gulf waters, creating a complex and dynamic snow forecast. Expect showers, with impacts and precip type driven by shower intensity, location, and the potential for training snow showers. Midweek to the weekend will mirror the previous snow shower regime, with ample opportunity for forecasts to bust. One item of note is the longer path that cold air at the surface will rotate around the parent system in the gulf, which could drive more vigorous instability but result in warmer surface temperatures along the coast. This could bring a rain/snow mix to the central and southern coastal locations under lighter showers, with heavier bursts of precip allowing all snow to push down to the surface. The exception will be the northern Panhandle and Yakutat where cold temperatures will keep the precip type as snow.

For reference, -10C at 850mb this time of year is near the 10th percentile for both Yakutat and Annette sounding sites, with surface temperatures forecasted to be at normal along the coast to slightly below normal for more interior locations.

AVIATION

Largely MVFR conditions prevail as a strong front makes its way north through the panhandle overnight. Periods of VFR are still possible for the next few hours in the northern panhandle as the edge of the front begins to reach them. As the front moves overhead, IFR to LIFR conditions will be likely during heavier bands of snow, bringing CIGs down to AoB 1500 ft with limited VIS. Areas of the northern panhandle still being influenced by strong northerly winds may see blowing snow, as well as locations that are being impacted by the strong winds associated with the front as it passes over. Gusts up to 30 to 35 kts will be possible in times of the strongest winds, though these are expected to calm down to AoB 10 kts behind the front.

Any locations south of a line from Petersburg to Sitka are either seeing fully rain, or are beginning to transition over to a rain/snow mix and then inevitably rain. Conditions are expected to continue to deteriorate through the next few hours for these areas of the southern panhandle before steadily improving towards the end of the period. These improved conditions may not be VFR, as low CIGs and continued snow showers will keep VIS lowered.

For the northern panhandle, snow is expected to prevail for the whole period. Along the Icy Strait Corridor, conditions are now beginning to deteriorate as snow moves in. A band of snow has made it up to Haines and Skagway which is especially bringing down conditions in Haines, though conditions are expected to improve through the early morning before the main impactful snow reaches them. LLWS at around 35 to 40 kts for most of the southern panhandle persists along the front, though this is expected to drop off quickly as the main impactful winds move out with the front. Juneau also is seeing some LLWS, though this is mainly due to strong winds coming out of Taku Inlet and is also expected to diminish behind the front.

MARINE

Inside (Inner Channels): Northerly winds continue across the northern inner channels while southerly winds begin to surge through the southern inside waters due to a strong low pressure system pushing northward. This low pressure system has brought gale force winds into Clarence Strait, Southern Chatham, and Sumner Strait. Currently the strongest winds are located near Cape Decision and Salmon Landing. There are also currently strong northerly winds out of Lynn Canal near Point Couverden. As this low moves north, it will strengthen the north/south oriented gradient allowing for a period of near gale to gale force winds throughout Lynn Canal. Another area to watch will be Cross Sound as winds are currently 30 kts from the east. As the low pushes northward, there will be a brief period where these winds quickly become southwest before once again becoming easterly. By Tuesday winds throughout the inner channels are expected to be southerly with the exception of far northern Lynn Canal.

Outside (Gulf and Coastal Waters): A strong low is currently moving northward into the southern gulf. This low has brought sustained gale force winds near 40 kts with storm force gusts near 50 kts into dixon entrance and to areas west of Prince of Wales Island. These stronger winds will continue over the southern gulf as the low continues to move northward to west of Baranof Island. These strong winds will continue into late tonight before diminishing. A couple of things also occur as this low moves northward. First, strong northeasterly winds push out of Cross Sound into the central gulf. Then as the low moves northward, winds quickly become southwesterly as another low develops in the far northern gulf. Along with strong winds, an area of 15 to 20 ft significant wave heights pushes into the southern gulf this evening. These waves subside to 8 to 10 ft starting late tonight through Monday.

Then to start the week, the low in the northern gulf will continue to allow widespread fresh to strong breezes of 17 to 27 kts across the gulf. At this time, showers will be the main story of the area allowing for times of reduced visibility and gusty winds. This showery pattern then lasts through the week.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Storm Warning until 1 PM AKDT Monday for AKZ318>322-325. Winter Weather Advisory until 7 AM AKDT Monday for AKZ323. Winter Storm Warning until 7 AM AKDT Monday for AKZ324. Wind Advisory until 1 AM AKDT Monday for AKZ325-330. Winter Storm Warning until 4 AM AKDT Monday for AKZ326. High Wind Warning until 1 AM AKDT Monday for AKZ332.

MARINE...Gale Warning for PKZ036-644-662>664. Small Craft Advisory for PKZ012-013-021-022-031-032-034-035-053- 641>643-651-652-661-671-672.