textproduct: Juneau

UPDATE...Update to aviation section to include 18z TAF issuance

SYNOPSIS

Key Messages:

- A low pressure system departs SW out of the area, with precipitation coming to an end. Outflow pattern develops through Sunday, allowing for drier and colder weather into next week.

- This outflow pattern will strengthen Monday and continue through the week bringing strong winds, colder temperatures, and moderate to potentially heavy freezing spray over northern and portions of the central inner channels.

- Mountain wave activity increases Sunday night with the potential for wind gusts up to 60 mph for Downtown Juneau and Douglas. A High Wind Watch is in effect late Sunday night through Monday afternoon.

LONG TERM

/Monday through Friday/ Over the week the primary threat continues to be outflow conditions, freezing spray, and very cold temperatures as cold arctic air infiltrates the panhandle, bringing a sudden return to true winter. Touching on wind first, we remain highly confident that we will see northerly winds of at least 25 to 30 knots spread across the northern inner channels by Monday, with a mountain wave event for downtown Juneau bringing frequent gusts of 40 to 60 mph. The main question is the potential of gale, to strong gale, force outflow winds ebbing and flowing through the week, which has serious implications on mariners safely navigating the inside. For now, the published forecast has strong gale force conditions in Lynn Monday into Tuesday. Guidance continues to slightly relax the north-south pressure gradient mid-week, which would result in winds diminishing to near-gale force conditions, perhaps even as low as strong breezes. However, do not let this catch you off guard. The winds will increase again to at least gales sometime by the end of the week, perhaps into the weekend, as a strong north- south pressure gradient builds back. Freezing spray really becomes a threat Monday, with freezing spray pumping through the inside all week. Heaviest freezing spray in Lynn Canal, Taiya Inlet, four corners area, Stikine Inlet, and Unuk River Inlet.

It will become very cold, below 0F in the north, single digits in the Icy Strait corridor, and teens to low 20Fs in the central and south. Wednesday night there is some signal that a shortwave trough will rotate around a stout ridge in the Pacific, perhaps bringing some snow to the region Thursday. Guidance usually struggles with a strong ridge over the region, we approach cautiously.

In the extended range, models are trending towards the development of stronger high pressure over the interior driving much colder air southward into the panhandle once more. This has the potential to produce stronger outflow conditions than earlier in the week, with sustained storm force winds along the northern inner channels, namely Lynn Canal, and dangerous freezing spray.

AVIATION.../through 18z Monday/

Generally VFR with pockets of MVFR for the northern TAF sites around Icy Strait Corridor and north as CIGs rise and VIS clears out with the system continuing to move southeast through the panhandle. Sites below the Corridor and southward to Ketchikan are looking at MVFR to IFR conditions continuing through early Sunday morning with CIGS AOB 2500 ft and visbys 2 to 5 SM. As the system continues to pass through Sunday morning and into the afternoon, conditions will continue to improve to VFR from NW to SW. An estimate on timing as the system departs the panhandle out of the southeast is improving conditions reaching Juneau very shortly, then from Sitka eastward to Petersburg by midday to early afternoon, with Ketchikan holding out longest til around later afternoon into the early evening. As the frontal band passes over, these central and southern areas will see VIS drop quickly due to the potential for snowfall. This snow will most likely be mixing with rain or at least very wet. Winds through the period 5 to 15 kts with gusts up to 25 kts for sites that typically are susceptible to a N to NE wind, especially Skagway.

By mid Sunday evening, overall clear skies and good VIS will prevail through Monday as outflow conditions develop with strong winds expected through the N/S inner channels of SEAK. The main aviation concern moving into early week will be isolated to occasional LLWS around 2kft due to persistent mountain wave development, as highlighted by the Alaska Aviation Weather Unit.

MARINE

Inside (Inner Channels): The anticipated low pressure system is currently around central SE AK and will continue to move southeast throughout the day. We are already seeing increased northerly winds around 25 kts across Lynn Canal this morning. As this low moves southward, winds will continue increase due to a tightening pressure gradient. By tonight, northerly gale force to strong gale force winds (34 to 47 kts) will spread across Glacier Bay, Lynn Canal, Stephens Passage, and Chatham Strait. These stronger winds will last well into the week as outflow continues. Along with these strong winds, decreasing temperatures will allow for freezing spray to develop. Freezing spray will also increase in intensity today with moderate freezing spray over the aforementioned areas by tomorrow. Areas of heavy freezing spray are also likely over portions of Lynn Canal and Glacier Bay.

Outside (Gulf and Coastal Waters): Near gale to gale force conditions will continue across the gulf as a low pressure system pushes SE across the panhandle. This system will bring gale force northwest winds to the central gulf with seas building to around 15 to 20 ft lasting through Sunday. This low is very likely to be a quick moving system, departing SE out of the panhandle by Monday morning. As this low moves southward, strong offshore and outflow conditions develop. Because of this outflow, mariners transiting along the N Gulf early next week should remain aware of areas of strong winds out of outflow prone areas like Cross Sound, Yakutat Bay, Disenchantment Bay, Alsek River Valley, and the Dangerous River Valley.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...High Wind Watch from late tonight through Monday afternoon for AKZ325. MARINE...Gale Warning for PKZ011>013-031-641-661. Small Craft Advisory for PKZ021-022-032>034-036-053-642>644-651- 652-662>664-671-672.