textproduct: Juneau

SYNOPSIS

Key Messages:

- Numerous light to moderate showers moving through tonight as a weak low pressure system moves inland across the Fairweather Range.

- A brief break in the persistent rain is possible Sunday night into Monday, however another front and round of heavier rain and wind push across the Gulf of Alaska into the Alaska Panhandle by Tuesday.

- Maritime interests need to pay attention to a strong front projected to move across the Gulf of Alaska by Tuesday, bringing Gale Force to potentially Storm Force winds to the central and eastern Gulf Tuesday into Wednesday.

LONG TERM.../Tuesday through Thursday/

An active fall-time weather pattern will continue across SEAK next week. Monday will start off with a ridge of high pressure over most of the panhandle, which could lead to fog development, with weaker onshore flow and light showers ahead of the next system. A progressive low and cold front will trek across the Gulf and reach Yakutat Monday afternoon before sweeping southeast across the panhandle Monday night into early Tuesday before weakening and stalling across southern panhandle, with onshore flow behind bringing steady rain into the panhandle. Total precipitation with this initial system will remain relatively limited, though a brief period of moderate to heavy rain and increasing southerly winds will develop ahead of the frontal boundary. Behind this initial system, a stronger low is forecast to deepen rapidly (~960 mb) as it lifts northeast into the northern Gulf of Alaska on Tuesday, stalling through midweek before gradually weakening and dissipating on Thursday. This strong low will quickly send another front and deeper moisture feed toward and through SEAK Tuesday into Wednesday, bringing moderate to heavy rain and strong gusty winds, along with severe marine hazards. South to southeasterly winds will intensify significantly on Tuesday, producing gale- force conditions in inner channels such as northern Lynn Canal and Clarence Strait, with gales (34-47 kt) and possibly storm-force winds (4855 kts) and combined seas exceeding 20 feet along outer coastal waters, mainly from Cape Spencer northward. By Thursday, conditions will improve behind the frontal passage and as the low in the northern Gulf weakens, though lingering onshore flow will sustain rain showers, while winds and seas slowly subside.

Persistent onshore flow with mainly cloudy skies and rain will keep temperatures cool and consistent through the period, with daytime highs in the mid to upper 40s (low 50s possible on Tuesday) and overnight lows in the upper 30s to low 40s.

AVIATION

We will continue to MVFR prevailing in patchy light rains across the Alaska Panhandle through tonight, with localized IFR in scattered to numerous periodic showers moving across on the east and southeast side of a low pressure area moving south of Yakutat. This pattern will continue into Sunday as a weak remnant trough persists across the Panhandle. We do see some breezy boundary layer winds (for the lowest 5 thousand feet or so) with gusts to around 30 kts through this evening, then winds diminish late tonight and toward morning. 05/Garmon

MARINE

Outside Waters: A weakening low in the northern gulf will continue to move inland along the northeast gulf coast Saturday night. This will accelerate dropping of winds and seas in the gulf Sunday as a weak ridge of high pressure briefly builds into the gulf for the tail end of the weekend. Seas look to drop from 8 to 13 ft across the gulf Saturday night, to 7 ft or less by late Sunday afternoon. The next weather of note will be a system potentially up to storm force set to move into the western gulf early next week, with winds and seas building through Monday.

Inside Waters: With the low in the northern gulf and associated front continuing to lift northward to the interior, winds along the inner channels north of Frederick Sound have picked up and will remain elevated through the evening hours Saturday before gradually diminishing late and through the day Sunday. Only Lynn Canal is expected to maintain breezy conditions a bit longer through first half of Sunday as a brief ridge rotates through the central gulf. With diminishing winds to end the weekend, some fog potential Sunday night particularly for the southern inner channels. Otherwise increasing winds early week with a strong system moving into the gulf and throwing a front towards the panhandle.

HYDROLOGY

A strong system is expected to move into the northern central gulf, reinforcing the existing low pressure system, and drawing a deeper fetch of moisture from northern Pacific. By Tuesday morning, this plume of moisture is expected to shift from southwest to southerly, and is likely to exceed 500 kg/ms IVT for around a 12-18 hour period for any given location in the Icy Strait corridor and NE gulf coast. Expecting Yakutat to be the big winner in terms of rain amounts, with near perfect perpendicular flow, strong WAA in the low levels increasing lift potential, and decent divergence aloft. With this, yakutat could see upwards of 6 inches during a 36 hour period, which is a little higher than a 2 year ARI event. For the Juneau and Gustavus areas specifically, rainfall amounts look very similar to the previous atmospheric river from last week which put Salmon River and Montana Creek into minor flood stage. Therefore, issued a hydrologic outlook for these areas for expected minor flooding at least.

There is a large wind component to this system as well, with guidance continuing to indicate unseasonably strong wind associated with this system. That being said, rain totals and rain rates look too weak to meet historical atmospheric and soil conditions at which isolated landslides have been observed.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Small Craft Advisory for PKZ012-013-022-031-053-641>644-651-652- 661>664-671-672.