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.../Monday through Wednesday/

Little change to the long term forecast and overall message as the pattern looks to stay unsettled. Low pressure will remain nearly stationary and very slowly weaken over south-central Alaska through the period. This will send multiple fronts across the panhandle and also work to reinforce persistent onshore flow. As a result, we will continue to see periods of rain, especially Monday into Tuesday with perhaps a bit less widespread precipitation for a time later Wednesday. As weak high pressure builds to our east over British Columbia and the pressure gradient tightens, we may see intervals of gusty winds, particularly in the favored areas over the northern panhandle. Model guidance is also suggesting that we could see a few thunderstorms, mainly over the coastal waters, but confidence was too low to include in the forecast at this time.

AVIATION.../through Sunday afternoon/

Generally MVFR VIS and CIGs this afternoon across the northern panhandle with VFR flight conditions prevailing across the southern panhandle. For PAYA, conditions will deteriorate through this evening and continue into early Sunday as a shield of rain moves onshore, with MVFR to possibly IFR VIS/CIGs expected. Conditions across the panhandle will deteriorate from northwest to southeast tonight as the shield of rain ahead of the front brings moderate to at times heavy rain, with widespread MVFR to possibly IFR VIS/CIGs expected through much of Sunday. Behind the front, partial improvements in flight conditions as rain will become more showery in nature. E to SE winds 8-15kt will increase to 15-25kt with higher gusts as the front passes overnight into Sunday morning. Winds will then diminish behind the front back down to 8-15kt by later Sunday morning, although southerlies will increase for PAGY 15-25kt and gusty. LLWS also expected ahead and along the frontal passage with winds 2kft aloft 35-45kt.

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 from 7 PM this evening to 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.