textproduct: Juneau

SYNOPSIS

Key Message:

- Heavy rain spreading eastward overnight and continuing through Tuesday for northern panhandle. Flood watches in effect.

- Wind gusts ranging from 40-55 mph with highest gusts near Yakutat and Skagway. Westerly wind shift from west to east Tuesday into Tuesday night.

- Thunderstorms possible Tuesday afternoons and overnight into Wednesday.

SHORT TERM

Modest changes to the ongoing forecast as the strong system moves into the NE gulf coast. Looking on satellite, a bulk of the higher IVT and warm moisture plume appears to be moving over the NE gulf coast, with Yakutat beginning to see heavier rain rates of 0.2 to 0.3 inches per hour. Similarly, easterly winds are beginning to ramp up in the inside channels. Main changes to the forecast is a slight trend up in rain totals for the Yakutat and Yakutat Bay area based on 12z runs. Rain totals now look to be around the 4.5 to 7.0 inch range over a 36 hour period, with amounts further at elevation in Yakutat bay possibly exceeding 10 inches. Slightly trended down the forecast in the Juneau area, as the heaviest rain looks to stay over the Yakutat area for longer. For more information regarding flooding, see the hydrology section.

Going into Tuesday afternoon, a sharp cold front sweeping across the panhandle from Yakutat to Ketchikan will quickly transition winds from southerly to westerly, with strong gusts of at least 40 mph along the leading edge. This has prompted an expansion of the wind advisories for Prince of Wales Island. Petersburg and Wrangell areas were excluded as the current thought is the front will shear apart to a degree these areas will not see 40 mph gusts. Furthermore, downgraded Skagway to an advisory, as a bulk of the energy moving northeast from the Prince William Sound area into the northern Yukon area. Therefore, the orientation of the pressure gradient does not look to lend itself toward 60 mph or greater wind gusts at this time.

Continued on the thunderstorm chances along the cold front sweeping westward to at least the Fairweather range. Behind the front, stronger lapse rates, divergence aloft, down to -35 Celsius temperatures around 500 mb, and CAPE values of around 400 J/kg could lead to some isolated thunderstorm chances along the coastline, with highest chances along the NE gulf coast north of Cape Spencer.

LONG TERM.../Wednesday through Saturday/... The front that brought heavy rain and strong winds on Tuesday will have all but cleared the southern panhandle by daybreak Wednesday. In its wake, persistent onshore flow will continue through Wednesday and into Thursday as the low lingers and slowly weakens in the northern Gulf of Alaska. Subtle shortwaves and upper troughs swinging around this low will keep higher precipitation chances with moderate to heavy showers and gusty winds across SEAK through Thursday. Behind the front, snow levels fall to 1,0002,000 ft on Wednesday over the northern panhandle. Snow showers will be possible along the Klondike Highway and upper reaches of the Haines Highway through Thursday, though any accumulation will remain light. As the low weakens and gradient relaxes behind the frontal passage, gusty southerly winds will slowly diminish through Thursday. The northern inner channels and into Haines and Skagway could still be quite gusty on Wednesday as the north to south gradient remains a bit tighter, and the High Wind Watch remains in effect of Skagway. As the Gulf low weakens further and shifts southeast toward the end of the week, showers will lighten and end from north to south Thursday night into Friday across SEAK. Upper-level ridging makes builds east across Mainland Alaska by late week, with SEAK on the eastern edge of the ridge. Ensemble and deterministic guidance generally showing high pressure building in the wake of the departing low, with clearing skies and drier offshore flow developing Friday and continuing into the early weekend. Daytime highs will remain in the 40s throughout the period, with overnight lows in the mid 30s to low 40s.

AVIATION

/ trough Tuesday morning / First front to push through the Northeast gulf and into the panhandle by Tuesday midday.

Second frontal band will move east and past the Yakutat area mid morning to afternoon. Expect a strong burst of strong gusty winds as the front approaches and a quick shift in the wind direction as it passes. Right now estimate for frontal passage is mid morning to early afternoon.

Winds Overnight in to early Tuesday. Turbulence and Wind shear, possible overnight for the coastal sites Yakutat/Sitka, and possibly reaching Gustavus and Klawock and many of the other TAF locations through afternoon.

MARINE

Inside(Inner Channels): Winds increasing to 25 to 30 kt through evenind and then up to gales by morning. The northern inner channels are already seeing sustained 15 to 25 kts, with Lynn Canal reaching closer to 30 to 35 kts by Monday afternoon. The strong southerly winds will spread through the rest of the central inner channels through Monday and into the southern inner channels by Tuesday morning. Anticipating periods of gale force winds to spread throughout the inner channels through Tuesday, bringing 6 to 8 ft wave heights through much of the panhandle. Winds in the southern and central panhandle should begin to decrease Tuesday night, while parts of the northern panhandle look to stay elevated through Wednesday.Will be able to fine the winds when they pick up.

Outside (Gulf and Coastal Waters): A strong gale force front towards the panhandle into Tuesday. With the initial system on Monday evening, southerly winds in the central gulf will increase to gale force with much of the coast seeing strong breezes to near gale force winds. A barrier jet also looks to form along the northern gulf coast from Kayak Island eastward to Icy Bay with this first system, bringing east to southeasterly strong gale force winds into Tuesday. Current thinking is sustained will be capped around 45 kts, but with localized gusts up to 60 kts. Another system looks to race up the western gulf coast overnight into Tuesday, strengthening the initial system and sending another strong front into the panhandle Tuesday into Wednesday. Winds across much of the western Gulf to sustained 45 kts gusts to 60 kts with higher confidence of a corridor of higher winds on the back side of the system. Widespread southerly 35 to 45 kt winds are expected to take over through the remainder of the gulf and along much of the coast Tuesday, which should steadily decrease through Wednesday. Strong southwesterly swell is also expected to increase, with the first system bringing 10 to 13 ft at a period of 10 to 12 seconds Monday and the second system quickly increasing to 20 to 25 ft at a period of 13 to 15 seconds. This will bring accentuated wave heights of 16 to 19 ft by Monday night and 25 to 30 ft through Tuesday. This will mainly be an issue for the northern and central parts of the gulf, with areas near Dixon Entrance staying closer to 12 to 18 ft at most.

$$

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Wind Advisory until 10 PM AKDT Tuesday for AKZ317. Flood Watch from 10 PM AKDT this evening through late Tuesday night for AKZ317-320-322-325. Gale Warning from 1 AM to 7 AM AKDT Tuesday for AKZ317. Wind Advisory from 1 AM to 10 PM AKDT Tuesday for AKZ318. Wind Advisory until 4 AM AKDT Wednesday for AKZ319. Wind Advisory from 9 PM this evening to 4 AM AKDT Wednesday for AKZ320>322-325. Wind Advisory from 1 AM Tuesday to 4 AM AKDT Wednesday for AKZ323-324-327. Wind Advisory from 7 AM Tuesday to 4 PM AKDT Wednesday for AKZ328. Wind Advisory from 10 AM Tuesday to 4 AM AKDT Wednesday for AKZ330-332. MARINE...Gale Warning for PKZ011>013-021-022-031>036-053-641>644-651-652- 661>664-671-672.