textproduct: Juneau

SYNOPSIS

Key Messages:

- Flood Watch in effect for Yakutat, Gustavus, Pelican, and Elfin Cove, and Juneau. Isolated landslides possible along the NE Gulf Coast, and Glacier Bay, near Steep Terrain.

- Strong winds push across the Gulf of Alaska into the Alaska Panhandle by Monday night and continues through Tuesday with widespread Wind Advisories in effect. Even stronger winds expected at Skagway with a High Wind Watch remains in effect.

- Maritime interests need to pay attention to the strong front projected to move across the Gulf of Alaska through Monday, bringing Gale Force o potentially Storm Force winds to the Gulf into Wednesday.

LONG TERM.../Wednesday through Saturday/

The front that brought heavy rain and strong winds on Tuesday will have all but cleared the southern panhandle by daybreak Wednesday. In its wake, persistent onshore flow will continue through Wednesday and into Thursday as the low lingers and slowly weakens in the northern Gulf of Alaska. Subtle shortwaves and upper troughs swinging around this low will keep higher precipitation chances with moderate to heavy showers and gusty winds across SEAK through Thursday. Behind the front, snow levels fall to 1,0002,000 ft on Wednesday over the northern panhandle. Snow showers will be possible along the Klondike Highway and upper reaches of the Haines Highway through Thursday, though any accumulation will remain light. As the low weakens and gradient relaxes behind the frontal passage, gusty southerly winds will slowly diminish through Thursday. The northern inner channels and into Haines and Skagway could still be quite gusty on Wednesday as the north to south gradient remains a bit tighter, and the High Wind Watch remains in effect of Skagway. As the Gulf low weakens further and shifts southeast toward the end of the week, showers will lighten and end from north to south Thursday night into Friday across SEAK. Upper-level ridging makes builds east across Mainland Alaska by late week, with SEAK on the eastern edge of the ridge. Ensemble and deterministic guidance generally showing high pressure building in the wake of the departing low, with clearing skies and drier offshore flow developing Friday and continuing into the early weekend. Daytime highs will remain in the 40s throughout the period, with overnight lows in the mid 30s to low 40s.

AVIATION... /Through 06Z Tuesday/

VFR conditions prevail across most of the panhandle. A widespread cloud shield has mostly cleared the southern region, improving cloud decks from OVC/BKN to SCT/FEW. However, this clearing has brought almost immediate fog formation, aided by saturated lower levels and calming winds. This is expected to significantly reduce VSBY to 1-2 SM through the early morning, impacting sites from Frederick Sound southward, though also including southern parts of Admiralty Island.

Meanwhile, the northern panhandle will remain in a lighter, showery regime tonight, ahead of the system tomorrow. Several sites, most notably PAJN, PAGS, and PAHN, seeing flight categories shift to MVFR this evening. CIGs expected to sit between 2000-3000ft, then shifting down to 1500-2500ft by the afternoon.

Finally, LLWS is likely near PAYA starting Monday afternoon into evening as the next system moves further east into the Gulf. This is driven by a stout lower level jet of 45-50 kt winds that will push the system toward the Northern Gulf coast and bring heavy rain and strong winds across the entire panhandle by Tuesday morning, further deteriorating conditions.

MARINE

Outside (Gulf and Coastal Waters): Conditions will quickly deteriorate from west to east across the Gulf Monday morning as a strong system sends a strong gale force front towards the panhandle into Tuesday. With the initial system on Monday, southerly winds in the central gulf will increase to gale force with much of the coast seeing strong breezes to near gale force winds. A barrier jet also looks to form along the northern gulf coast from Kayak Island eastward to Icy Bay with this first system, bringing east to southeasterly strong gale force winds into Tuesday. Current thinking is sustained will be capped around 45 kts, but with localized gusts up to 60 kts. Another system looks to race up the western gulf coast overnight into Tuesday, strengthening the initial system and sending another strong front into the panhandle Tuesday into Wednesday. Main forecast change was increasing winds across much of the western Gulf to sustained 45 kts gusts to 60 kts with higher confidence of a corridor of higher winds on the back side of the system. Widespread southerly 35 to 45 kt winds are expected to take over through the remainder of the gulf and along much of the coast Tuesday, which should steadily decrease through Wednesday. Strong southwesterly swell is also expected to increase, with the first system bringing 10 to 13 ft at a period of 10 to 12 seconds Monday and the second system quickly increasing to 20 to 25 ft at a period of 13 to 15 seconds. This will bring accentuated wave heights of 16 to 19 ft by Monday night and 25 to 30 ft through Tuesday. This will mainly be an issue for the northern and central parts of the gulf, with areas near Dixon Entrance staying closer to 12 to 18 ft at most.

Inside (Inner Channels): Winds across the southern inner channels remain calm and variable as transient high pressure quickly moves across the area ahead of an approaching front. The northern inner channels are already seeing sustained 15 to 25 kts, with Lynn Canal reaching closer to 30 to 35 kts by Monday afternoon. The strong southerly winds will spread through the rest of the central inner channels through Monday and into the southern inner channels by Tuesday morning. Anticipating periods of gale force winds to spread throughout the inner channels through Tuesday, bringing 6 to 8 ft wave heights through much of the panhandle. Winds in the southern and central panhandle should begin to decrease Tuesday night, while parts of the northern panhandle look to stay elevated through Wednesday.

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 600 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. There are lower probabilities of around 30% to see a 5 year event for 36 hours for the NE gulf coast, and even higher ARIs are possible further into Yakutat Bay. These higher ARIs look to extend down the coast and into the Glacier Bay area, with may areas along south facing slopes exceeding 5 year return intervals and approaching on 10 year over a 36 hour period. Therefore, added Elfin Cove, specifically for the mountains to the north, the NE gulf coast, and Glacier Bay to the Flood Watch. This is mainly for areal flooding of low lying areas and ponding of water. That being said, the wind component of this system has wind gusts greater than 40 mph at elevations greater than 500 ft, and greater than 60 mph at elevations around 2000 ft. Current thinking is the high rain rates combined with higher return intervals in the upper rainfall ranges (higher percentiles, lower probability) leads to an increased risk of isolated landslides in steep terrain based on historical atmospheric conditions.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Wind Advisory from 4 PM this afternoon to 10 PM AKDT Tuesday for AKZ317. Flood Watch from this evening through late Tuesday night for AKZ317-320-322-325. High Wind Watch from this evening through Wednesday afternoon for AKZ318. Wind Advisory from 4 PM this afternoon to 4 AM AKDT Wednesday for AKZ319. Wind Advisory from 9 PM this evening to 4 AM AKDT Wednesday for AKZ320>322-325. Wind Advisory from 1 AM Tuesday to 4 AM AKDT Wednesday for AKZ323-324-327. Dense Fog Advisory until 7 AM AKDT this morning for AKZ328. Wind Advisory from 10 AM Tuesday to 4 AM AKDT Wednesday for AKZ330-332. MARINE...Gale Warning for PKZ011>013-021-022-031>036-053-641>644-651-652- 661>664-671-672.