textproduct: Juneau

PREV DISCUSSION......ISSUED AT 425PM AKST

SHORT TERM...The next system moves in from the west Friday night into Saturday morning, bringing gale to potentially storm force winds along the outer coast as the warm front approaches and moves through. This front will bring a round of heavy snowfall across the panhandle and overruns the colder air in place after the low Thursday night has moved out of the area and colder temperatures return even down to the southern panhandle.

This front will bring warmer temperatures across the panhandle from south to north into the southern and central panhandle as warm air is advected in from the southwest, both the warm air and deep moisture being tapped into from a deep 500 mb trough to the west digging down to around 30-40N and directing southwesterly flow into the panhandle. Heavy snowfall will begin to transition to rain during the day Saturday into Saturday night, beginning with the southern outer coastline and moving inwards towards the northeast as the front pushes through and winds pick up. Sitka and PoW will see the transition to rain first by the afternoon to evening hours as the winds shift to a more southerly direction and strengthen and the surface warms. The rest of the central and southern panhandle will begin to see this transition to rain Saturday night into early Sunday morning.

Though the transition timing has changed with guidance today showing that Icy Strait corridor may not see the amount of warming initially expected with the northerly flow still remaining coming out of Lynn Canal and Taku Inlet, keeping temperatures at their maximum closer to the low to mid 30s, though uncertainty remains on how warm exactly the surface will become into Sunday. The downtown area is expected to see the highest potential of increasing to 36 to 38 degrees with rain in the afternoon due to the southeasterly flow following the front. There remains some uncertainty of the timing and areas seeing these different precipitation types, and for how long these conditions will be expected. Overall there will be an increase in temperatures and a mix to potentially some rain still by the afternoon hours for Gustavus and Juneau, before cooling again into Monday.

Snow amounts remain largely the same for Saturday, while Sunday will see continued heavy snowfall across the northern panhandle as an arctic boundary keeps those areas from warming as much as the rest of the panhandle. These heaviest snowfall accumulations of over 12 inches in 24 hours Sunday are expected for Yakutat, Haines, Skagway, and it is very likely for Juneau and Gustavus to see 10 to 14 inches if the warm air does not make it up to Icy Strait and reduce the snow accumulation or transition fully to rain. The southern panhandle is seeing largely the same rainfall amounts Sunday, with the heaviest concentrated on Ketchikan. This follows some of the AR and EFI tools narrowing down the more extreme precipitation amounts and higher confidence right around Ketchikan, with between 3 and 5 inches of rain expected in 24 hours with the heaviest rates during the evening into Sunday night. The rest of the southern panhandle will still see some higher amounts, with between 2 and 3 inches for PoW up to Petersburg and Wrangell. The largest threat for these areas is the heavy rainfall shortly following the heavy snow, and high freezing levels allowing for snow melt. See the hydrology section below for more details.

LONG TERM.../ Monday to Wednesday / In the mid levels of the atmosphere the long wave trough is closing off to a more simplified closed low pattern over the central gulf but Wednesday. Meanwhile the surface feature goes from and extend low pattern to a single low as well, and becomes more vertically stacked.

The biggest challenge we were seeing that the warming may not go as far north. Gradients in Lynn Canal appear to want to stay north, and this would keep the cooler air filtering south to the Juneau area. So nudged temps from from about Icy Strait Corridor / Cross Sound to Juneau area / north down some and this should push the mix south ward or out of the area.

Southern panhandle Monday dealing with the AR that slides south and ends going into Tuesday. The amounts anticipated mean that we are still watching potential flooding issues. As the main flow pattern shifts south, temperatures will slowly cool and push to the central panhandle and the mix back to the southern panhandle.

The northern panhandle Monday will see the snow with moderate to locally heavy amounts as the last of the frontal systems so may see the warning that are out may linger into the Monday time frame. This is all up to how the warming permeates the inner channels headed to Monday.

With the surface low sitting into the central gulf onshore flow will continue so chance level PoPs into the Wednesday night are likely.

AVIATION.../Until 06Z Sunday/...A potent frontal system will be moving into the Panhandle starting this evening. PAYA has started to see snow with VIS and CIGS lowering to MVFR conditions this evening. Conditions will continue to lower through late tonight to be IFR by day break on Saturday and persist all day. The snow from this front will continue to progress eastward, starting its push into the rest of Southeast Alaska through Saturday morning. For the rest of the Panhandle, expect to see conditions lower to the MVFR category between early to mid-morning Saturday, depending on how far southeast you are, then approach & lower into the IFR category by Saturday afternoon. Snow will be the main element hampering visibilities and CIGS with this system through Saturday night.

For winds, lingering enhanced winds from remnant northerly outflow will remain through this evening for the northern Lynn Canal / PAGY but they will diminish through late tonight. For the Outer Coast, including PAYA, PASI, & PAKW it will start to get breezy/gusty late tonight as the front gets closer to those areas. Winds will pick up, becoming breezy for the rest of the region thereafter mainly for the southern half of the inner channels. Additionally, LLWS will also begin to increase up to range from 30 to 50kt around 2 kft out of a generally south to southeasterly direction. These LLWS conditions will start for the Outer Coast starting late tonight and progressing southeastward through the Saturday afternoon and persisting into the evening time frame.

MARINE... Outside (Gulf/Coast):

Friday evening ESE winds increase along the northern coast as a storm force low moves into the Gulf, reaching peak intensity through the daylight hours Saturday. We will see extensive strong-gale force conditions, with storm force conditions in favored areas like Cape St. Elias and Cross Sound/Palma Bay/Fairweather Grounds. One challenge for this afternoon was significant wave heights, with guidance struggling to agree on extent and magnitude of winds, thus impacting wave potential. Have settled with significant wave heights reaching near 20 ft to 25 ft Saturday from the ESE, focused near 10 seconds, with the main focus of energy from the Fairweather grounds toward Cape Suckling. If storm force conditions are more extensive near the Fairweather grounds, 25 to 30ft seas aimed toward the northern coast are more likely. For Cape Edgecumbe south toward Dixon Entrance, expecting southerly strong gale force conditions to gale force, with the higher winds/seas favored for areas offshore of Chichagof/Baranof.

A southwest fetch window is opening up for the Gulf over the weekend into the start of next week, with ESE Force 9 seas along our coast becoming SW 15 to 20ft focused at 11-14 seconds by Sunday, most wave energy aimed at the coast of PoW. For Monday/Tuesday, while the main parent storm resides in the Gulf, a few other disturbances will move along our coast, freshening up ESE winds to gale force at times. While the primary energy will likely be focused from the SW, these ESE winds will create large and confused seas.

Inside (Inner Channels):

As of Friday afternoon, winds were beginning to subside as a weakening gale force low moved south toward the Pacific Northwest. As a storm force low moves into the Gulf late Friday, expecting winds to become southerly for areas south of Icy Strait, increasing to minimum of gale force for much of the inside Saturday along with heavy snowfall.

The main focus Friday afternoon has been in the magnitude of wind strength, with a few hours of strong-gale force conditions likely as the front moves over Saturday afternoon. Favorable areas in Clarence Strait like Snow Passage and just southwest of Nichols Passage could see storm force conditions; caution advised. For Icy Strait expecting easterly winds of strong breezes to near-gales with Pt. Couverden likely gale force. Wind forecast for Lynn Canal remains a difficult endeavor, with some hint at a southerly push Saturday into Sunday for southern Lynn Canal. For now, the published forecast has leaned heavily on the GFS ensemble pressure gradient for northerly winds in Lynn Canal with the Euro Ensemble showing a more modest pressure gradient suggestive of light to southerly winds.

HYDROLOGY...A rain on snow event is expected for the area starting late Saturday into early Sunday starting for the southern panhandle. Temperatures are expected to warm into the mid 40s to low 50s through the southern panhandle as well as snow levels increasing to around 5,000 to 7,000 ft. Farther north, the temperatures for the central panhandle and Icy Strait corridor warm up to the mid 30s to low 40s while snow levels warm up to 2,000 to 4,000 ft during this time as well. Most of this warming is expected to occur during the day Sunday, continuing into early Monday for the southern panhandle. 24 hour rainfall amounts on Monday are expected to reach up to 3-5" of rain during the day for the southern panhandle, while in the central panhandle, 24 hour totals are closer to 2-3.5" of rain. Most of the heaviest rain rates are expected Saturday evening through early Monday morning. We have issued a flood watch for Sunday and Monday from Sitka eastward to Petersburg and south to Dixon Entrance due to the significant snow amounts on the ground, what is expected to fall on Saturday, and the heavy rain and snow melt.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Storm Warning until 6 AM AKST Monday for AKZ317. Winter Storm Warning from 9 AM Saturday to 6 AM AKST Monday for AKZ318-319. Winter Storm Warning from 3 AM Saturday to 6 AM AKST Monday for AKZ320-325. Winter Storm Warning until 3 AM AKST Sunday for AKZ321-322. Winter Weather Advisory from 3 AM to 9 PM AKST Saturday for AKZ323-327. Winter Storm Warning from 3 AM to 9 PM AKST Saturday for AKZ324. Winter Storm Warning from 9 AM to 9 PM AKST Saturday for AKZ326- 328>330-332. Flood Watch from late Saturday night through Monday afternoon for AKZ326>330-332. Winter Storm Warning from 9 AM Saturday to midnight AKST Sunday night for AKZ331. MARINE...Storm Warning for PKZ644-652-664-671. Gale Warning for PKZ031-032-034>036-641>643-651-661>663-672. Small Craft Advisory for PKZ013-021-022-033-053.