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 Friday/

Tuesday will begin with moderate to heavy rainfall and gusty southerly winds across northern panhandle with an occluded front pushing ashore with a deeper feed of moisture. Throughout the day, a rapidly deepening surface low will lift northeast into the northern Gulf, with a quick moving cold front traversing the Gulf and through the panhandle, clearing the southern panhandle on Wednesday morning. Along and ahead of the front, an atmospheric river will tap into a deeper feed of subtropical moisture, with heavy rainfall and strong winds feeding into the panhandle, with highest rain amounts and strongest winds across the northeast Gulf coast and northern panhandle. South to southeasterly winds will intensify, producing gale-force conditions in inner channels such as northern Lynn Canal and Clarence Strait, with widespread gales (34-47 kt) to storm-force winds (4863 kts) and combined seas exceeding 20 feet along outer coastal waters, mainly from Cape Edgecombe northward.

As the primary low stalls and weakens in the northern Gulf through the end of the week, onshore flow and subtle troughs swinging around the low will keep higher precipitation chances with moderate to heavy showers and gusty winds across SEAK through Thursday. Quite a bit of model discrepancy by the end of the week, but general trend is for the low to weaken further as it shifts southeast, with a ridge of high pressure building in its wake, bringing clearing skies and drier offshore flow.

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

Snow levels may initially be low enough for snow or rain/snow mix near White Pass early Tuesday morning, but will quickly rise throughout the day as southerly winds pick up ahead of the front. Snow levels will fall down to 1-2kft behind the front Tuesday night/Wednesday and snow showers will be possible along the Klondike Highway and the upper reaches of the Haines Highway through Thursday, although any accumulations look to be light for now.

AVIATION.../through Sunday evening/

A low pressure center, located just off the coast near Yakutat has brought moderate to heavy rain showers across the region alongside breezy winds in the lower levels with gusts reaching around 30 kts, before diminishing late tonight and toward morning. As the low weakens, winds aloft begin to dwindle and the threat of LLWS subsides into the evening hours, though stronger winds gusts could generate turbulence below mountain top levels.

MVFR conditions will continue to prevail with lighter rain showers triggering over higher terrain through tonight, accompanied by localized IFR conditions during the passing of scattered periodic showers. In between these showers, conditions improve to high-end MVFR or low-end VFR with CIGs generally settling between 2500 and 3500 ft. While extensive clearing is not expected overnight, brief breaks in cloud cover as winds calm may allow for shallow/patchy fog formation near Wrangell and Petersburg, causing drops in VSBY. This showery pattern will continue into Sunday as a weak trough persists across the panhandle, which will eventually give way to high pressure, providing additional clearing by Sunday night and an overall improving trend.

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.