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

The start of the long term looks to remain active with the low pressure continuing to persist. This will allow for clouds and precipitation to continue to impact the area. This low eventually dissipates while a stronger low looks to pass south of the area and high pressure builds in Canada. Behind this low, high pressure is expected to move in to the Gulf behind this stronger low which may allow for us to see a break Sunday evening into Monday morning. Headed into the start of next week, ensemble guidance wants to bring another low into the western Gulf. The main difference between EPS and GEFS guidance is where this low comes from. EPS wants to bring a low up from the south on Monday and have it merge with a low that is expected to persist in the Bering Sea before moving towards the Cook Inlet area Tuesday. This low then tracks into Prince William Sound Tuesday evening into Wednesday. GEFS guidance wants to bring the low from the Bering Sea on Monday and track it across the Alaska Peninsula and Cook Inlet before moving remaining offshore near Prince William Sound.

AVIATION.../Through 6z Friday/

Widespread deteriorating conditions expected as a strong occluding front moves towards the panhandle. The winds associated with this front are just reaching the outer coast of the panhandle at the time of this discussion, with PASI and PAHY already gusting to 30 kts. 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 30 kts with gusts up to 40 kts, and periods of strong LLWS upwards of 50 kts near 2 kft increasing through 00z. Moderate to heavy rainfall, gusty winds, and LLWS will spread NNE'ward into the rest of the panhandle as well, but conditions are expected to stay mostly MVFR to VFR with gusts up to 30 kts and LLWS around 35 to 45 kts after 12z Thursday. Behind the initial warm front moving in overnight, a brief break in heavy rainfall may be possible for the southern panhandle before the cold front sends a second surge of moisture and winds into the panhandle mid morning. Behind the front, VIS and CIGs are expected to stay relatively lowered as another surface disturbance jumps into the panhandle by the very end of the TAF period.

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 persistent 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 occurring 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.