textproduct: Juneau

SYNOPSIS

Key Messages:

- A larger, more impactful system to move into the Gulf Wednesday night, impacting SE AK overnight into Thursday and through the start of the weekend.

- A Flood Watch is in effect for the southern panhandle with rain rates as high as 0.25 to 0.3 inches per hour possible.

- Winds will continue to increase Thursday into the weekend. A Wind Advisory is in effect for the southern panhandle.

LONG TERM

Active weather continues for the long term as low pressure continues to remain in the Gulf for the start of the weekend. With the low staying in place, some onshore flow will continue allowing for moisture to remain across the area. Guidance today has moved away from the idea of the remnants of Typhoon Koguma impacting the panhandle for the weekend. Instead, GEFS and EPS are pointing towards the low moving into British Columbia. The main low that has been affecting the panhandle will still be in the area bringing increased winds across the southern panhandle. Moving into the start of next week, guidance still has some good divergence on model outputs but conditions could remain somewhat active although there is a chance we see a break in the weather before another low looks to potentially move into the western Gulf by Monday evening.

AVIATION

/through 00z Saturday/ No major changes to ongoing forecast this afternoon. Predominate VFR flight conditions across the panhandle with CIGS AoA 3500ft with pockets of MVFR ceilings around 2000 to 3000ft. Conditions will begin to deteriorate from 06-09z, persisting through the rest of the TAF period until Thursday afternoon as a strong low in the W Gulf of Alaska sends the first of two fronts into the panhandle. The worst flight conditions through Thursday will centered around the southern terminals, from Sitka to Petersburg southward to Ketchikan and over to Klawock with MVFR condition and periods of IFR visibilities due to heavy rainfall, sustained winds 20 to 30kts with gusts up to 40kts, and likely periods of strong LLWS increasing through 00z upwards of 50kts near 2kft. Further north, for Juneau and terminals along the Icy Strait Corridor and over to Yakutat, predominant MVFR flight conditions, sustained winds 10 to 20kts with gusts up to 30kts, increasing potential for LLWS around 35 to 45 kts after 12z Thursday morning with moderate to heavy rainfall expected to persist through the day. Best flight conditions across the area will be near Haines and Skagway, with MVFR to low end VFR flight conditions and winds around 10 to 20kts albeit some wind shifts expected 18 to 22z Thursday afternoon.

Simply put, flight conditions deteriorate to predominate MVFR overnight Wednesday and continue through Thursday with moderate to heavy rainfall, strongest wind gusts up to 40 kts across the southern terminals, and likely widespread LLWS across much of the area.

MARINE

Outer waters: Main changes to the ongoing forecast is the expansion of storm force winds off the coast southwest of the Fairweather Range beginning tonight and continuing into the morning hours of Thursday. As this front pushes northward, the area of highest winds will shift near Cape St. Elias before diminishing. As for the rest of the front, widespread strong gales for much of the outside waters will persist through the late morning, before focusing around the Dixon Entrance area through Friday morning. Long duration gale force winds for Dixon Entrance are due to multiple wave of energy moving up along the front. Wave height corresponding with highest wind speeds could reach between 23-25 ft, both from ESE wind waves and 20 ft at 11 seconds southerly swell, maximizing Thursday morning. Expecting to see 15-20 ft waves in the Dixon Entrance area Thursday and Thursday night, largely driven by a longer fetch up Clarence Strait and persistant gale force winds.

Inside Waters: A strong atmospheric river moves into over the panhandle beginning tonight, with inside channel wind speeds beginning to react substantially early Thursday morning. Expect to see largely strong breezes to near gales in most inner channel waters with the exception of Glacier Bay and Northern Lynn Canal. For those areas, expecting aloft winds to be too weak to meaningfully increase wind speeds greater than 15 knots, with Lynn Canal likely flipping northerly as the front moves northward through the central panhandle.

On the secondary system moving in on Thursday night, may see shifting winds on the north two quadrants of the low, Stephens Passage area and a majority of Chatham Strait. Extreme southern Chatham Strait (near ocean entrances), Sumner Strait, and northern Clarence Strait are all expected to see a rapid wind shift from SE to the WSW, possibly associated with convective storms, gusty winds, and a few lightning strikes.

HYDROLOGY

/Wednesday night through Friday morning/ A strong incoming atmospheric river will move into the panhandle beginning early Thursday morning and continuing through Friday morning. Two distinct frontal features make up a bulk of the heavy rain for the central and southern panhandle: The first during Thursday morning through Thursday afternoon, and the next Thursday evening into Friday morning. Confidence for the precipitation amounts and gusty conditions following into Thursday night has increased, with guidance narrowing in on an area extending from Petersburg and Wrangell down to Ketchikan and Metlakatla. IVT values look to range between 500-750 kg/ms, with more confidence on the area moving into the panhandle leaning towards 750 kg/ms for both waves, with the second wave still appearing to push from the south into the southern panhandle. Ketchikan and Metlakatla continue to be the target of opportunity here, with rain rates possibly exceeding 0.3 inches per hour, and up to 0.25 inches elsewhere. These rates are expected to be sufficient enough for at least minor flooding on small creeks and streams, particularly given the duration of the event.

Alongside these heavy rainfall amounts looking to be around 5 year return intervals for the southern panhandle, the increased confidence on elevated winds of 20 to 35 mph with gusts up to 40-50 mph associated with the second wave brings the possibility of isolated landslides occuring in areas south of Frederick Sound.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Small Craft Advisory from 10 AM to 1 PM AKDT Thursday for AKZ322. Wind Advisory from 1 AM to 4 PM AKDT Thursday for AKZ323-325-327- 328. Flood Watch from Thursday afternoon through Friday afternoon for AKZ326>330-332. Wind Advisory from 1 AM Thursday to 4 AM AKDT Friday for AKZ329- 330-332. MARINE...Storm Warning for PKZ644-663-664-671-672. Gale Warning for PKZ021-031-034-036-641>643-651-652-661-662. Small Craft Advisory for PKZ013-022-032-033-035-053.