textproduct: Juneau

SYNOPSIS

Key Messages:

- Strong winds and highest rain accumulations anticipated to peak overnight Saturday. Heavy rainfall at higher elevations can cause smaller creeks and streams to rise rapidly through Sunday morning.

- Unstable air behind the main front brings a risk of isolated thunderstorms on Sunday along the northeast Gulf coast.

- Unsettled conditions are expected to persist into early next week as multiple fronts bring occasional breezy winds and heavier showers.

LONG TERM.../Tuesday through Thursday/

Unsettled weather will continue into at least the beginning of this period as low pressure meanders while slowly weakening over south-central Alaska. The heaviest rainfall Tuesday into early Wednesday will likely be centered over the northeast Gulf Coast and northern panhandle with lighter amounts farther south. A few thunderstorms still also appear possible, especially over the coastal waters, but we did not include thunder in the forecast at this time given the uncertainty and anticipated low coverage. As the aforementioned low finally disintegrates on Thursday, we should see an overall improvement in conditions. A separate, more intense low pressure system may approach the southern panhandle late Thursday and beyond, but model agreement on the track and timing of the system is quite low. This will be monitored closely in future forecasts. After this potential system, high pressure will attempt to at least briefly build into the Gulf.

AVIATION.../Through 06Z Monday/

A front being pushed in to the Panhandle this evening, and is bringing MVFR ceilings and visibilities. With heavier showers, IFR conditions appear to be possible tonight. So far, the highest rainfall rates have been along the Gulf Coast and Northern Panhandle. With 35-45 kt winds 2000 feet AGL, this will lead to low-level wind shear concerns. However, as the front diminishes, so will the threat for low-level wind shear. The winds are expected to diminish across the area from north to south. Before another round of rain after 21Z Sunday, a brief time of high-end MVFR/VFR appears possible, but not a guarantee.

Behind the front impacting the area at the time of writing, a low in the Bering Sea will push another round of rain toward the Northern Panhandle Sunday evening. This will likely bring MVFR ceilings/visibilities to Southeast Alaska. With cold air aloft, this may lead to some thunderstorm development, but confidence in this occurring was too low to include in this aviation update. Overall, the system in the Bering Sea is expected to weaken as it moves east into the Gulf of Alaska. Some of the stronger winds aloft associated with the system aloft may try to impact Klawock and Ketchikan toward the end of the TAF period. However, the strongest winds look to remain south of the Panhandle.

MARINE

Outside: Conditions will continue to deteriorate Saturday afternoon as a gale force low and assortment of fronts moves into the coast. As of this writing at 1400 AKDT Saturday, Cape St. Elias is reporting gales from a barrier jet, with 18 ft fresh seas. ASCAT winds (satellite derived winds) from Saturday morning continue to match high resolution guidance well. As a front approaches the coast this evening expect southerly 35 to 45 knot sustained winds and seas building to 15 to 20 ft for much of our coast. The heaviest conditions will be from Cape Edgecumbe to Cape St. Elias; however, the coast of Prince of Wales will certainly see near-gale to gale force conditions.

As the front moves off into the Panhandle Sunday, expecting ESE winds to persist along the northern coast, with southerly winds becoming southwest along the coast of the Alexander Archipelago. Winds will vary from moderate to fresh breezes. One component is a large influx of southwest wave energy, driving fresh seas with significant heights near 9 to 12 ft. Conditions likely improve Wednesday bringing a short break before another large system moves into the Gulf.

Inside: Not a great night to be moving around on a small boat in the inner channels. Make ready for a strong front Saturday night into Sunday. Expecting the front to reach Cross Sound and Sitka near 5pm to 7pm, quickly moving northeast through the inner channels overnight. By and large sustained winds will be ESE strong breezes for the area, with areas of near-gale to gale force. Current forecast favors Sumner Strait, southern Chatham, and northern Clarence Strait to see near-gale to gales as the front moves over.

At first, ESE winds will flow from Clarence up the inside, with easterly winds out of Taku, Icy Strait, and Cross Sound, with southerly winds building after the front, moving up Lynn Canal and Glacier Bay.

HYDROLOGY

A stronger system is expected to move into the panhandle Saturday into Sunday, bringing periods of moderate to heavy rain. Main changes to the ongoing forecast is an increase to expected accumulations in the southern panhandle by up to half an inch. Compared to the previous forecast, that still puts most areas between the 1.5 - 3.0 inch mark. Furthermore, higher rainfalls are most likely on south to southwest facing mountain faces. During the peak of heavier rainfall during the overnight hours, rain rates could exceed 0.15 inches per hour in the central panhandle and 0.25 inches per hour in the southern panhandle. Moderate to heavy rates are expected to continue for any given location for a period of around 12-18 hours before decreasing. Upwards of 4 inches will be possible for higher elevations. Due to the short nature of the heavier rainfall, smaller creeks and streams will rise quickly, may possibly reach bankfull conditions, but are not expected to flood at this time.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Wind Advisory until 10 AM AKDT Sunday for AKZ323-327-328-332. MARINE...Gale Warning for PKZ036-641>644-651-652-661>664-671-672. Small Craft Advisory for PKZ011>013-021-022-031>035-053.