textproduct: Juneau

SYNOPSIS

Key Messages:

- Moderate to heavy snow continues over the panhandle into Friday morning.

- Northerly outflow intensifies as snow exits the region later Friday into the weekend with strong gales developing for the northern inner channels late Friday night.

- Temperatures continue to trend down through the weekend with the strong outflow winds.

LONG TERM

/Saturday through Thursday/ Mid to long range shows a rather amplified and constantly changing upper level pattern from the weekend into next week. The weekend features a sharp ridge over the Aleutians, Bering Sea, and western Alaska while a deep trough cuts over Western Canada, the panhandle, and the eastern Gulf of Alaska. This amplified pattern gets replaced by Tuesday into Wednesday with a strong trough diving south through the state from the Arctic that is forecast to dominate the upper pattern over the area by late next week.

For the forecast there are two regimes that we are concerned about. The first is the strong cold outflow that will be occurring from Saturday into Monday. The second is a new storm system that will be approaching from the NW Tuesday into Thursday on the leading edge of the upper trough that is dropping south that will likely bring more accumulating snow to many areas of the panhandle. First the outflow. The forecast has largely not changed all that much with widespread gale force conditions still expected for many northern inner channel areas (and possible min storm for Lynn Canal and maybe Taku Inlet) through at least Sunday before diminishing into Monday. Some details have changed however, particularly Skagway (for high outflow winds) and Juneau (very strong Taku wind/mountain wave development possible over downtown) where high wind watches have been issued starting Friday night and lasting into Sunday night. The Taku Wind event at Juneau has the potential to be the strongest we have seen this season with cross barrier flow reaching 50 to 60 kt combined with an inversion above mountain tops. The critical level is not completely ideal as there is not much directional shear (more speed shear with a speed min approaching near 5 to 15 kt), but it is setting up around 500 mb for most of the event. So wind gusts around downtown Juneau and Douglas could reach 70 or 80 mph. Seas for some of the northern inner channels that have long north to south reaches (like Lynn Canal and Stephens Passage) have also been raised a couple feet to account for more fully developed seas from the long duration strong winds blowing down the long linear fetch. The freezing spray forecast remains mostly unchanged with a wide area seeing at least light freezing spray expected this weekend (heavy freezing spray for areas like Lynn Canal, Stephens Passage, Glacier Bay, and Taku Inlet). The cold temperatures and wind will also combine to create cold wind chills in some areas as well, particularly along the Klondike Highway where wind chills could plunge to near 35 below in the higher elevations of the highway. Other areas have the problem of where the wind blows there is enough mixing to warm air temperatures while areas that see the colder temperatures don't have any wind so wind chills in other parts of the panhandle may get cold, but may not get to cold weather advisory criteria.

Into mid next week, We completely flip the script with outflow dieing off, temperatures starting to warm, and a new storm system coming in from the NW. Precipitation looks to be starting up as early as Tuesday for most areas but could wait until Tuesday night. Also while many areas will be warming, this is in comparison to the temperatures that we are expecting to see over the weekend, so widespread 30s for highs while lows dip into the 20s. So when the precip does arrive it will likely be in the form of snow for many areas (except the southern panhandle) with accumulations likely adding up to a couple inches mainly over the outer coast and central panhandle.

AVIATION

Mostly MVFR in light snow across the northern 2/3rds of the Alaska Panhandle this afternoon, but we will see a trend down to IFR along the outer coastal regions by this evening as a low pressure system approaches from the northwest and we see additional dynamic forcing for periods of heavier snow and lower ceilings Yakutat down through Sitka before midnight. The snow will become somewhat heavier at times (periodically to IFR) for the inner channel airports late tonight into tomorrow morning, with snow gradually clearing from NW to SE 18Z-24Z on Friday. As for winds, not much change to our thinking there with easterly winds beginning to pick up in the PAYA area after 09Z. The winds in areas north of a line from Elfin Cove to Juneau will begin to pick up throughout the morning hours tomorrow, with northerly gusts increasing to 35-40kts in the Haines and Skagway areas as outflow winds start to increase with strong high pressure building over the Yukon Territory. 05/Garmon

MARINE

Outside (Gulf and Coastal Waters):Thursday morning winds of gentle to moderate breezes were prevalent along the coast, with two primary wave systems present; the dominant was WSW swell of 3 to 6 ft at 12 seconds masking SE fresh seas of 1 to 3 ft from the south. Moving through Thursday a low will begin to mature in the gulf, with storm force northwest winds building out of Cook Inlet. These NW winds will build large NW seas, likely reaching near 20 ft in the central gulf, and some NW energy hitting the Chichagof,Baranof, and PoW coast, Friday. Strong gale to storm force outflow winds will also quickly build the northern coast Friday, spreading south into the weekend. The simple message is that mariners transiting our coast should be aware of strong outflow from major ocean entrances and inlets, bringing freezing spray and large northerly fresh seas of 18 to 20 ft. Favoring the coast will limit wave potential from limited fetch availability with the exception of Yakutat Bay, Chatham, and Sumner entrances, but then exposure to freezing spray is increased greatly.

Inside (Inner Channels):The simple message is that by this weekend most inner channels along and north of Sumner Strait will see gale to strong gale force conditions, with freezing spray. Major river inlets like Taku, Stikine, and Unuk, will see particularly intense conditions. Peak winds Sunday.

Winds of gentle to moderate breezes are a welcome treat early Thursday as a very diminished surface pressure gradient resides over southeast. This story will rapidly change Thursday night as the low-pressure system responsible for snow and light winds shifts south, increasing southerly winds to fresh breezes in the central inner channels. This is the first signal that conditions are about to change, with a rapid shift to northerly winds Friday morning, speeds quickly ramping up to gale force in Lynn Canal and Taku, strong breezes to near gales in Chatham and Stephens, by Friday afternoon. Conditions continue to deteriorate Friday night, with extensive gale force to strong gale force conditions over most passage along and north of Sumner Strait. Model Guidance is under doing winds in Sumner Strait, relying on historic data from poorly positioned surface observations that are sheltered from northerly winds, extreme caution is advised for mariners planning to transit the inside this week. You will encounter gale force winds, freezing spray, with the most extreme conditions in Glacier Bay, Lynn Canal, and Stephens Passage. Major river corridors like Taku, Stikine, and Unuk will also see gale to storm force winds and heavy freezing spray.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Storm Warning until 3 AM AKST Friday for AKZ317. High Wind Watch from late Friday night through Sunday evening for AKZ318. Winter Weather Advisory until 9 AM AKST Friday for AKZ320-321- 324-325. Winter Storm Warning until 6 AM AKST Friday for AKZ322. Winter Storm Warning until 9 AM AKST Friday for AKZ323-328. High Wind Watch from Friday evening through Monday morning for AKZ325. Winter Weather Advisory until 6 AM AKST Friday for AKZ326-327- 329. Winter Weather Advisory from 6 PM this evening to 9 AM AKST Friday for AKZ330-332. MARINE...Storm Warning for PKZ053-651. Gale Warning for PKZ011>013-022-643-644-652-663-664-671-672. Small Craft Advisory for PKZ021-031-032-641-642-661-662.