textproduct: Juneau

SYNOPSIS

Key Messages:

- A second release from Suicide Basin has started with an expected crest level of 10 feet early Friday.

- Onshore flow will keep mainly cloudy skies and rain showers for the northern panhandle on Friday, while high pressure ridge will bring partial clearing and drier conditions for the southern panhandle.

- A stronger system and weak atmospheric river will bring gusty winds, elevated seas, and moderate to heavy rainfall for the weekend.

LONG TERM.../Sunday through Tuesday/

A low pressure system will enter the Gulf of Alaska this weekend, bringing gale-force winds to the outer coast along with periods of moderate to heavy rainfall associated with a weak atmospheric river. A stronger wave arrives by early Sunday morning. As the low slowly dissipates near south-central AK, it will meander and track multiple fronts across the panhandle. This setup, reinforced by a consistent slew of upper level troughs and divergent flow aloft, keeps precipitation in the forecast for the extended period, although overall impacts are expected to diminish gradually heading into next week. One thing of note is as the low dissipates, the pressure gradient over the northern panhandle becomes more north to south oriented, causing a potential increase in winds within Lynn Canal through Monday and Tuesday.

Impacts associated with this weekend system will initially start along the NE Gulf coast and as far south as Baranof Island, also upwind of higher elevations. From Sunday through Monday, heavier precipitation will push south across most areas, particularly targeting the Misty Fjords region. The highest confidence for 24- hour rainfall accumulations during Sunday's stronger wave ranges between 1.5 to 2.5 inches, with localized amounts reaching 4 to 5 inches over higher terrain. However, at this time there is a low (25%) chance that lower elevation areas surrounding Icy Strait, such as Juneau and Gustavus, could exceed 2.5 inches. A significant southerly jet will move along the coast Saturday, shifting southwesterly by Sunday morning and likely bringing 35 to 40 knot sustained winds from Cape Spencer north to Cape Suckling. Overnight Saturday into Sunday presents the greatest concern for elevated and gusty winds over the southern panhandle and inner channels, then trending on the decline Monday morning.

AVIATION.../Through 06z Saturday/

VFR to occasional MVFR conditions prevail late this afternoon. Scattered showers also continue to affect the region, particularly across the northern and central panhandle. This trend will likely persist through the overnight hours. MVFR may become increasingly predominant after 09Z-12Z tonight under persistent onshore flow and a return to lower ceilings, especially north. However, as a weak ridge slowly pushes into the southern panhandle, there could be some improvement in conditions after 15z-18z Friday.

MARINE

Outside: Current SITREP across the mighty Gulf Thursday early afternoon: southwest winds of moderate breezes, with dominant seas out of the southwest 5 to 7 ft near 7 to 9 seconds. Underneath these seas are swell groups from the central and south Pacific. Thursday afternoon the parent low continues to decay along the northern coast, expecting a surface high to dominate the southeastern gulf, limiting the surface pressure gradient allowing winds and seas to diminish further. For Friday morning, expecting wind at or below moderate breezes, with seas at or below 5 ft. A short break.

Attention turns to a strong-gale force low developing along the Aleutian Storm Track which will push into the western Gulf by Saturday morning. Watch those winds Friday night, south-southwest becoming southeasterly will signal the approaching front, with winds increasing to strong breezes over much of our coastal zones through early Saturday morning. Folks transiting the PWS Cross Sound route will see gale force condition by Saturday morning, with conditions continuing to diminish further through the day. Current forecast Saturday afternoon/evening has trended sustained winds up, to strong-gales, with gusts to storm force.

Winds continue to build through the day Saturday for the coast of the Alexander Archipelago, with gale force forecasted for the Fairweather Grounds by Saturday afternoon, with gales spreading south through Saturday night.

5 ft seas along the coast Friday build to large and confused seas of 15 to 20 ft from Fairweather Grounds to Cape St. Elias coast by Saturday late afternoon, with 12 to 15 ft short period seas along the remainder of our coast. These significant wave heights will ultimately depend on where the strongest winds associated with the front setup along our coast, stay tuned. Either way, 15 ft fresh seas are guaranteed, with the challenge trying to nail down where 18 ft to 20 ft seas could propagate; much higher confidence for the northern coast.

Inside: Certainly, a tricky forecast over the next 48 hours for the inside. Simply put, portions of the northern inner channels will continue to hold onto about 15 to 20 knots of wind through Saturday as a low shifts off into Canada. Main problem areas will be northern Stephens, Lynn Canal, and northern Chatham. For areas along and south of Frederick Sound, expecting winds at or below 15 knots.

Additional forecast focus continues to be a developing gale force low and assortment of fronts south of the Aleutians, which will shift into the Gulf over the weekend. Expect southeasterly winds to begin to ramp up over much of the inner channels early Saturday afternoon, becoming widespread fresh breezes, with localized areas of strong breezes. As a front moves across the region Saturday evening, expecting winds to reach strong breezes, with localized areas of near-gale force from Icy Strait south. Southeasterly winds shift to more southerly, flowing up Lynn Canal Sunday and building to near-gale force in Clarence Strait.

HYDROLOGY

Incoming short duration plume of moisture for Saturday into Sunday Icy Strait and southward. IVT values looking to exceed 500 kg/ms for roughly a 6-12 hour period. This is mainly due to a strong warm front moving up from the south, increasing snow levels to 6000-8000 ft. This is allowing increased moisture presence, with PW values around an inch, which is roughly 80th to 90th percentile compared to climatology. While this is not entirely unusual for this time of year, wind transport up to 50 knots is contributing to the previously mentioned 500 kg/ms exceedence. This combined with continued rainfall and saturated soils means that any rainfall will likely translate directly into runoff, and smaller streams likely responding quite quickly. Biggest areas of concern are in the Icy Strait corridor, although recent guidance have the heaviest rain shifting southward somewhat out of this area. Currently expecting to see some river rises, particularly small streams, but confidence was not high enough to see any river flooding at this time. Therefore, a flood watch has not been issued, but upcoming conditions will continue to be monitored.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...None.