textproduct: Juneau

UPDATE

After the 06z TAF issuance. No big changes to the forecast that was out. The weakening band of higher clouds are pulling SSE, and a marine deck is moving to the coastal and inner channels of the northern panhandle. Movement has been slow so essentially kept forecast the same.

PREV DISCUSSION......ISSUED AT 411 pm AKDT Jun 5

SYNOPSIS...

Key Messages:

- Rain in the central and southern panhandle tapers off through Friday night as a weak frontal band breaks apart.

- Chances of showers linger into the weekend with seasonably cool temperatures, leaning towards drier and slightly warmer conditions for early next week.

- Another front approaches the southern panhandle Sunday, with the main impact being strong S to SE'erly winds, gusts, & increased seas along the eastern gulf, the Dixon Entrance, & up into Clarence Strait.

SHORT TERM...A decaying front continues to slowly slide southward over the panhandle, with the northern extent of rain just south of the Icy Strait corridor. In the wake of this front, low level clouds are expected to linger along the inner channels which should hamper any significant cooling of temperatures overnight. Noticeable in satellite imagery is the continued development of a marine layer in the gulf stretching from just east of Cook Inlet across the northern Gulf and south towards Buoy 46085. This layer is a result of weak surface troughing extending eastward from Kodiak Island that is being capped by ridging aloft.

This overall setup is expected to continue into Saturday, as the low south of Haida Gwaii continues to push into the Pacific northwest and British Columbia and the associated front continues to lose energy. A small area of positive vorticity advection will support some isolated shower activity primarily for the northern panhandle Saturday, though chances should remain low (below 40%). The southern panhandle should clear out in terms of precipitation, as surface ridging rotates through, though this will also lead to onshore flow eventually Saturday.

For the other half of the weekend, a low is expected to spin up along a cold front that is progressing eastward from south of the Aleutians. Upper level support for this low is poor though as the upper level jet is expected to remain fairly zonal and also stay predominantly south of the Gulf. In the mid levels, a closed low circulation is expected to gradually be sheared apart, which should result in diminishing momentum for the front as it pushes across the Gulf and approaches the panhandle Sunday. As of this forecast, the southern and central panhandle outer coast look to have the highest chances of seeing some light precipitation from this system. The inner channels, particularly north of Frederick Sound, look to stay relatively dry during this period, though mid to high level clouds spreading over the area cannot be ruled out. For more on what to expect to start next week, see the long term discussion below.

LONG TERM.../Monday through Friday/...The upcoming week will be shaped by several evolving systems. The main story begins with the tail end of a weak low pressure system entering the Gulf on Sunday. This system will bring elevated southeasterly winds to the southern panhandle, specifically from Hecate Strait up through southern Chatham Strait, accompanied by light precipitation across the southern region on Monday. Current model runs indicate this low is tracking further south and drying out, so expect winds and precipitation to taper off fairly quickly by Monday midday.

Looking toward the mid-week period, the pattern shifts to mostly zonal flow from Tuesday evening through Wednesday and cooler, more seasonable temperatures follow. A weak front is expected track across the panhandle. While this front brings increased wind potential to the Lynn Canal area on Tuesday evening due to a tightening pressure gradient, the overall dynamic forcing remains weak. A 500mb trough building Tuesday night may support light rain showers into Wednesday morning, though any activity will be largely terrain-driven, characterized by onshore flow and primarily isolated to the southern region. Post-front, high pressure will build south of the panhandle, near Haida Gwaii, and although this ridge is expected to be relatively weak, it may allow for some clearing. High temperatures look to remain in the mid 50s to mid 60s, north to south respectively, and a slight warming trend is expected by the end of the week.

By Friday, a stronger low tracks into the western Gulf from the central Pacific. An associated shortwave trough could bring a surge of moisture to the region, but ensemble models disagree on timing and track. The GEFS favors a faster, southerly path toward the southern panhandle by Thursday afternoon, whereas the ECMWF Ens suggests a slower progression toward the north coast near Icy Bay with a more disorganized flow against high pressure. Stay tuned for updates throughout the week.

AVIATION.../Until 00Z Sunday/...As far as CIGs & VISs are concerned, many areas will primarily stay in the MVFR/IFR flight category range through the 24-hour TAF period. For the southern Panhandle, this will be due to a weakening rain band associated with a weakening low pressure center located just to the south of Haida Gwaii diving southeastward away from Southeast Alaska & toward Vancouver, British Columbia. For the northern Panhandle, this will be due to a flat dirty ridge that has built-in, causing a low marine layer stratus deck to develop for the northern 2/3 of the Outer Coast, including PASI & PAYA, & the western 2/3 of the Icy Strait corridor, including PAGS. Areas like PAGY in the extreme northeastern Panhandle & PAKT in the extreme southern Panhandle should remain in the VFR flight category for the majority of the period. It is possible that these 2 locations may temporarily dip into the upper MVFR flight category late tonight. SFC winds will remain rather breezy/gusty for the northern Lynn Canal region, especially for the PAGY area, due to a tight pressure gradient that will remain in place over that area. No LLWS concerns are anticipated through the rest of the period.

MARINE...A low south of the Panhandle, just to the south of Haida Gwaii, will continue to slowly move southeastward toward Vancouver, British Columbia through this evening. A band of rain rotating around said low will linger over the central & southern panhandle, drifting southward, before dissipating & falling apart through tonight. A flat dirty ridge of high pressure builds-in over the eastern Gulf into the weekend, giving onshore flow & low marine layer stratus clouds for the northern 2/3 of the Outer Coast & into the Icy Strait corridor. Then, another low & associated front approach the Panhandle & dive southeastward, moving past the Panhandle for the latter half of the weekend, bringing winds & seas up for the southeastern Gulf, Dixon Entrance, & Clarence Strait.

Outside Waters(Eastern Gulf of Alaska): Seas will remain between 5 & 7 ft & winds will remain 20 kt or less until Sunday when sustained winds increase up to between 25 & 30 kt with the highest values, particularly over the southeastern Gulf, Dixon Entrance, & southern Clarence Strait areas, & significant wave heights build back to between 7 & 9 feet when another low & associated front approach Southeast Alaska & dives southeastward, passing by & moving away from the our region early next week. Southerly swell up to 3 ft is expected through Sunday morning, with the largest swell to the south. The swell will diminish to 1 to 2 feet late Sunday through early next week. Winds will progressively diminish to less than 15 kt & winds will subside to less than 3 ft for the entirety of the eastern Gulf through Tuesday as that low continues to weaken, move southeastward away from the area, & the pressure gradient further relaxes.

Inside Waters(Southeast Alaskan Inner Channels): Winds over most of the Inner Channels will generally stay around 15-20 kt or less through early next week with Lynn Canal/Taiya Inlet experiencing a bit breezier conditions due to a periodically tighter pressure gradient. Winds will generally follow a diurnal sea breeze / land breeze cycle through Saturday, diminishing overnight before ramping back up during the daytime hours. On Sunday, winds will increase up to around 25 to 30 kt for southern Clarence Strait / the Dixon Entrance & seas will build up to around 7 ft, once again, as another low & its associated front approach Southeast Alaska & dive southeastward, bypassing the area through early next week. Winds will progressively diminish to less than 15 kt & winds will subside to less than 3 ft for the entirety of the Inner Channels through Tuesday as that low continues to weaken, move southeastward away from the area, & the pressure gradient further relaxes.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Small Craft Advisory for PKZ012-036-641-642-644-651-652-661>664- 671-672.