textproduct: Juneau

AVIATION UPDATE

For the late morning forecast update for the airports, we are generally trending VFR from north to south and clearing out the lower clouds through 02Z tonight. Generally, we kept the trend of the light to moderate northerly flow working its way south across the area through tonight, with winds 2-8 thousand feet AGL holding up in the 15 to 20 kt range late tonight and into morning across the southern areas. The northern areas should see winds decouple a bit over the land areas and the boundary layer supporting the notion of a weak inversion and radiational fog production 12Z-17Z at Yakutat, Gustavus, Juneau and Petersburg. Otherwise down south from Klawock, Ketchikan and Wrangell we kept just enough mixing in the boundary layer (especially lowest 2 thousand feet) to inhibit fog production early tomorrow morning.

SYNOPSIS

Key Messages:

- Light rain begins to end Friday with drier conditions expected by Saturday.

- Patchy fog this morning with areas at a mile or less visibility.

- Northerly outflow winds begin to impact many inner channels into Saturday night.

SHORT TERM... Early Friday morning rain will continue to push south, leaving behind some fog in protected places. While the parent system drifts south, a north-south pressure gradient will form across the Panhandle, resulting in northerly outflow conditions impacting much of the inner channels. One item that may weaken winds is the potential for a sea-breeze to form Friday afternoon. For further discussion on marine winds, see the marine section below. As outflow settles in Friday we expect drier conditions to take hold over the region, leaving behind a pleasant sunny day or two, with gusty northerly winds at elevation in the mountains.

LONG TERM...Dry weather and clearer skies expected Saturday as ridging sets up to the west over the Gulf, and with the low to the SE will allow for offshore flow. The N 15 and 25 kt winds are expected down Lynn Canal, Stephens Passage, and Chatham Strait overnight into the morning Saturday, with up to 30 kt winds possible down Lynn Canal. The gradually weakening pressure gradient along with the diurnal heating combating the offshore flow moving into the daytime will limit some of this northerly flow into the afternoon and evening hours on Saturday. The clearer skies will enable warmer temperatures during the daytime Saturday across the panhandle, as well as allow for some cooler nighttime temperatures Saturday night, and bring potential for sea breezes in some areas during the day. Winds across the panhandle will diminish to light and variable overnight into Sunday morning, picking up again into Sunday night as the next system approaches.

The ridging offshore will begin to break down into Sunday as the next system approaches from the NW Gulf. This system shows higher confidence today at being colder aloft, with -7 to -9 C temperatures at 850 mb and a cold low center at 500 mb, but still the warmer temperatures at the surface keep some uncertainty on precipitation in the forecast at this time for Monday night. Still expecting this to be a more convective system due to the colder temperatures aloft and warmer sea surface temps, bringing more showery precipitation. This will move into the NE coast during the day Sunday before pushing E across the rest of the panhandle overnight through Monday. A rain / snow mix is expected in the overnight hours for the N panhandle, becoming rain by morning. The rest of the panhandle will see rain as the system moves through later that morning through the day Monday.

Some mixing potential returns to the panhandle into Monday evening and the overnight hours as snow levels drop and temperatures aloft decrease, though precipitation chances will gradually diminish into Monday night from W to E as well. Any mixed precipitation is not expected to accumulate much at all, especially as daytime temperatures remain in the high 30s to low 40s Monday. Expecting around a trace of snowfall for the northern panhandle Sunday through Monday night, with sea level locations staying below 0.5 inches for snowfall. Majority of the QPF for this system is expected to impact the NE Gulf coastline, between 0.6 to 0.8 inches of QPF for Yakutat, largely falling as rain aside from during the overnight hours.

AVIATION.../ through Friday night / Moisture band across the southern portion of the panhandle will weaken through the day, and tapering off by the evening hours. Clearing conditions early this morning across the northern portion has allow morning fog to develop for some communities like Gustavus, Juneau, and Yakutat with visibilities under a mile. So expect some flight hazards due t the fog or low stratus. Central panhandle may see that as well. By afternoon or evening hours expect much of the panhandle to be reporting VFR conditions, although patchy fog could possible form overnight leading to impact Friday night to Saturday.

MARINE... Outside (Gulf and Coastal Waters): Northwesterly winds continue to expand and evolve across the eastern Gulf over the next 24 hours, with speeds of moderate to strong breezes expected overnight Friday. Sea state is currently dominated by southwesterly swell of 10 seconds near 5 ft and some chop at 4 seconds. Expect the primary wave direction to become northwesterly along the coast Friday afternoon, increasing to 8 ft west of Dixon Entrance by Saturday afternoon.

Inside (Inner Channels): Main threat over the next 24 hours is northerly outflow winds, with fresh to strong breezes impacting Glacier Bay, Lynn Canal, Chatham Strait, Stephens Passage and Clarence Strait. Freezing spray concerns are limited given warmer air temperatures. Winds begin to relax Saturday night, with southerly winds increasing by Monday.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...None. MARINE...Small Craft Advisory for PKZ012-661.