textproduct: Juneau

Mid Morning and 18z Aviation Update

Forecast updates this morning remain focused on wind speeds and gusts. Marine winds across the northern inner channels remain strong with sustained winds around 40 kts and gusts up to 60 kts, specifically over the Eldred Rock area and near Point Couverden. Land winds near Juneau have become stronger than initially anticipated due to a strong mountain wave event. Due to these stronger winds, a High Wind Warning has been issued for downtown Juneau and Douglas Island, including Thane, with gusts up to 60mph expected.

The forecast remains largely on track for precipitation types and amounts. Snow has started to transition to a wintry mix across the far southern panhandle as snow continues to fall across the central panhandle near Wrangell, Petersburg, and Kake. As the far southern panhandle transitions to all rain, there may be a short period of time where freezing rain develops. Snow will continue to move north reaching the Icy Strait Corridor, including Juneau, Saturday afternoon. Heaviest snowfall for the Juneau area and Icy Strait Corridor is still anticipated late Saturday night into Sunday.

AVIATION

/through Sunday morning/ Panhandle currently split into 2 regimes as a front pushes into the southern panhandle. Starting for the north, along a line and north of Sitka to Angoon, current VFR flight conditions with overcast CIGS AoA 6000ft. For the S Panhandle, along and south of a line of Sumner Strait, deteriorating conditions as front pushes northward with IFR to MVFR conditions with intermittent LIFR visbys due to heavier snow. Through the rest of the afternoon, aforementioned front and snow showers will continue to push north and weaken before stalling along the central panhandle, with precipitation changing over to predominately rain for S Panhandle sites like Ketchikan and Klawock by Saturday afternoon. During this changeover to rain for S Panhandle, should see a short duration of freezing rain as surface winds turn S-ly and temperatures begins to climb. Flight conditions by Saturday evening will be predominate MVFR or worse across the panhandle as the system weakens and stalls. A reinforcing secondary surge of moisture will push through the panhandle by Sunday morning with another round of heavy snowfall expected for the central and northern TAF sites along the Icy Strait Corridor, including Sitka, Petersburg, Wrangell, Juneau, Gustavus.

Strong winds for Skagway continue throughout the TAF period, with NE wind speeds between 25 and 35 kt expected with gusts up to 55 kt. The strongest winds expected as the front approaches and the gradient tightens into Saturday afternoon and evening. The rest of the panhandle will see increased winds between 10 and 20 kt as the front moves through, along with gusts to 20 to 30 kts. With another front approaching into tomorrow, the southern panhandle will see another increase in winds at the end of the TAF period. LLWS remains a concern across the southern and central panhandle with southerly 30 to 40 kt winds at 1500 to 2000 ft expected today and remaining over the southern panhandle through the TAF period. The northern panhandle around Icy Strait Corridor including Juneau and Gustavus, as well as up along the NE Gulf coast near Yakutat, will see some wind shear with northeasterly winds of 30 to 40 kts at 2000 ft lasting through the TAF period, even as surface winds turn SE for Juneau and as surface winds remain light for Gustavus and Yakutat.

SYNOPSIS

Key Messages:

- Cold temperatures continue, with quite cold wind chills continue along White Pass.

- Gusty outflow winds down Lynn Canal and mountain wave into the Downtown Juneau area Saturday.

- A front moves northward through the panhandle this weekend, bringing snow to a majority of locations. Confidence is increasing that locations south of Sumner Strait will switch to rain through the latter half of the weekend.

- Moderate to heavy snow rates expected for the central panhandle on Sunday, with precipitation continuing into early next week

LONG TERM.../Sunday through Tuesday/

A low jumping into the southern gulf Saturday is expected to send a high precipitation- producing front into the southern panhandle this weekend. This front will steadily climb northward through the weekend before pulling back early next week. Persistent cold temperatures combined with the ample moisture being carried in with this system should result in widespread precipitation spreading up the panhandle through the period.

The biggest change that was made was shifting the timing of the system up a few hours, which in turn will bring snow to the southern panhandle in the early hours of Saturday morning. As the main precipitation band moves north following the coastal mountains through Saturday morning, the central panhandle will start to see light snow accumulate followed by parts of the Icy Strait Corridor, mainly Juneau. Light rates will trickle out through Saturday night before the front sends a reinforcing wave of moisture up through the panhandle, bringing the more anticipated moderate snowfall rates through the central panhandle and into the Icy Strait Corridor. The main forecast challenge today was determining where this precipitation would fall as rain or snow, as the initial frontal band is looking to force a pocket of warmer air into the southern panhandle earlier than expected. Models are showing more agreement on the front temporarily pushing temperatures around 40 degrees up into the far southern panhandle Saturday afternoon, which has indicated to us that the initial snow the southern panhandle receives will most likely mix into rain through the remainder of the weekend. As a result, the winter storm watch that was issued yesterday has been updated to a winter weather advisory to better encompass those accumulations. A winter storm watch was also issued for the extended central panhandle area on Sunday. This includes all communities from Juneau and the Icy Strait Corridor down to Wrangell.

Totals still widely vary this far out, though moderate to heavy rates still remain possible. On Saturday, accumulations between 2 and 5 inches are possible anywhere south of and including Kupreanof Island. Other locations may see around an inch as the system attempts to spread north. Sunday, the higher accumulations move to the central panhandle, with between 5 to 12 inches possible from Juneau down to Port Alexander. The interior panhandle closer to the coastal mountain range can expect to see the higher end of these totals. Due to the vastly different microclimates around SE AK, isolated locations may receive up to 13 inches of snow in that 24 hour period. Confidence largely decreases on the front reaching further north, though the possibility still remains of communities in northern Lynn Canal receiving light snow accumulations from this system. With the southern panhandle remaining above freezing during that period, heavy rainfall between 1 to 2 inches is expected Sunday. Since the timing of the system was shifted up, precipitation on Monday begins to pull back out of the northern panhandle through the afternoon, with rates steadily diminishing overnight. Though final snowfall totals may widely vary from place to place, the longer duration of this event, combined with the potential for rain on snow in some more southern locations, could lead to impactful conditions by the beginning of next week. Another system looks to queue up behind this one, and combined with the arctic boundary shifting back southward, may keep active winter weather in the forecast through next week.

Hyder is the odd one out with this system, as the location may allow for cold air to stick around longer. A weak atmospheric river directed into BC south of the panhandle looks to hook up along the southern parts of the coastal range, drastically increasing QPF amounts for Hyder in particular. If they are able to hold onto their cold temperatures in combination with such increased moisture making it that far inland, total snow accumulations between 25 and 30 inches from Saturday through Monday may be possible.

Strong outflow winds begin picking back up Saturday, persisting through next week reaching at least gale force through the northern inner channels and out of Cross Sound. Gaps and drainage channels along the gulf coast will serve as outlets for strong winds to funnel through, with pockets of storm force sustained winds looking probable Sunday into Monday. Freezing spray will remain an issue in the inner channels and along the NE gulf coast with these elevated winds, which could become heavy at times. These outflow winds pose a challenge for the forecast, as the strong northerly flow will attempt to force the front to stay more south and limit available moisture to produce accumulating snow.

MARINE

Outside: Northeasterly outflow wind speeds decrease tonight. Then, outflow gap winds increase again, up to around 35-45 kt, for the same areas for the weekend. Some freezing spray is possible for the northeastern gulf.

Inside: The outflow pattern continues through Saturday across the northern panhandle, wind speeds pick back up to 25 to 35 kts, with near 35 to 40 kts back and gusts to 50 to 55 kt in Lynn Canal as a low pressure system tracks northward, tightening the pressure gradient over SE AK. Wind directions will, more-or-less, go unchanged through this time frame across the northern panhandle. Freezing spray continuing for Stephens Passage, Northern Chatham, Icy Strait Corridor, and Lynn Canal through the weekend, progressively getting heavier towards early week. A weak system will push into the southern panhandle through Saturday, with a swap to southerly winds within Clarence Strait.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...High Wind Warning until 6 PM AKST this evening for AKZ318-325. Winter Storm Watch from late tonight through late Sunday night for AKZ320>327-329. Winter Weather Advisory until 9 PM AKST this evening for AKZ326- 327-329. Winter Weather Advisory until 3 PM AKST this afternoon for AKZ328-330-332. Winter Storm Warning until 6 AM AKST Monday for AKZ331. MARINE...Heavy Freezing Spray Warning for PKZ012-053. Storm Warning for PKZ651. Gale Warning for PKZ011>013-022-053-643-644-663-664-671. Small Craft Advisory for PKZ021-031-032-034-036-641-642-652-661- 662-672.