textproduct: Juneau

UPDATE...After 06z

Not much concerns for the TAF's tonight with most sites showing good flight weather. A band of light snow over the central panhandle. Recently a small pocket of patchy fog forming near Ketchikan, the has gone to lower clouds Friday evening.

PREV DISCUSSION......ISSUED AT 354 pm Fri Mar 27

SYNOPSIS...

Key Messages:

- Outflow winds continue for northern channels and NE gulf coast through Friday.

- Multiple systems pushing into the southern panhandle will bring rounds of wintry precipitation to Ketchikan, Annette, and Prince of Wales Island.

- Potential for a weak front to move in Monday.

SHORT TERM.../Through Saturday night/ The panhandle remains sharply divided between two weather patterns through the weekend. Aloft, the upper level trough remains anchored in place with its SE flank located just south of the area. Closer to the surface a weak low has moved inland across the southern panhandle, and will continue meandering around the area before falling apart on Sunday.

The gradient between the weakening low and a high over British Columbia will keep outflow winds continuing through the time frame, although anticipate that they will be on a weakening trend as the low fills and the pressure gradient slackens. Consequently, the northern half of SE AK will continue to enjoy drier weather, significant breaks in the clouds for much of the time, and nothing more than a few flurries precipitation wise. Temperatures will plunge to well below normal overnight; with some sheltered areas reaching the teens or single digits, before spiking back upwards through the afternoon hours as the late March sun makes its impact felt.

The southern panhandle by contrast will see bands of showers continue to move through, with snow prevailing during the evening, overnight, and early morning hours. Given continued strong conditional instability in the atmospheric column up through ~500 mb, think that the primary limiting factor for snowfall accumulation will be daytime heating. While overnight temperatures will be cool enough to support accumulating snow, warmer surface temps during the late morning/afternoon timeframe will largely cut off snow accumulation, with snow melting as fast as it can fall in some locales. While winter weather advisories have been issued for the southern panhandle, final snow totals will ultimately be highly variable, with anywhere between 4-15 inches of snow near sea level through Saturday morning. The low will weaken through the latter half of Saturday, and by Sunday, will have fallen apart entirely.

Even as the low falls apart through Sunday, a weak shortwave trough approaching from the W looks set to bring chances of snow showers back across the outer coast and the southern and central panhandle as we head into the start of the upcoming week. For additional information, see the long range forecast discussion.

LONG TERM.../Sunday through Wednesday/...The long term forecast continues to be relatively uneventful, with only a few changes made. The northern panhandle is expected to stay mostly dry through the weekend and into early next week. Sunday looks to be more of a break day for the south, allowing the whole panhandle the chance to see breaks in the clouds as residual showers from the previous deteriorating low taper off. An upper level trough persists through the period with the southernmost tip largely remaining south of the panhandle, steering the bulk of the active weather into British Columbia and away from SE AK. A 500 mb low moves along the deepest part of the trough Sunday into Monday, proceeded by an upper level shortwave in the northern gulf. The surface inflection associated with the shortwave may bring light precipitation along the outer gulf coast of the panhandle through Monday, though this doesn't seem to have enough energy to make it much further inland than the outer coast.

A surface low following the upper level trough jumps into the southeastern gulf Monday afternoon, though it will still be too far south for the bulk of the frontal band to make it to the panhandle. Guidance currently suggests that the warm frontal band will catch up with the latter half of the shortwave band, which would bring a more organized band of precipitation through the southern and part of the central panhandle Monday night through Tuesday morning. This band may even make it as far north as the Icy Strait Corridor, and PoPs have been raised to reflect this. There is a potential this will just manifest as flurries for any location north of Angoon. Cold temperatures aloft (-8 to -10 degrees C) would keep most of this precipitation as snow, with the chance to mix into rain through midday as daytime temperatures rise. Daytime highs in the upper 30s to low 40s, combined with the increased sun angle, will make it so most snowfall does not accumulate until the evening or nighttime hours when temperatures decrease, especially for locations along the water.

The low is expected to depart quickly, dipping south Tuesday night into Wednesday. Uncertainty remains for the exact impacts through the early week, as model guidance is still somewhat split on the position of the low and resulting front. The GFS has come more in line with the EC, though still moving out of the area much faster and not lingering through Wednesday morning. Southerly winds will briefly increase going up through the inner channels with the frontal band, though they aren't expected to be very strong. Both before and after the low moves through, light outflow looks to develop with the pressure gradient tightening over Lynn Canal. This is only expected to reach up to 25 kts through Lynn Canal and Stephens Passage, as well as around Point Couverden and out of Cross Sound. This will help to keep skies clear through the northern panhandle and extending down through the central panhandle into the early week, potential clouding up more by Tuesday with the weak frontal band. Through Tuesday evening, depending on how quickly the low moves out of the area, skies will start clearing from north to south until a majority of the panhandle is seeing partly cloudy skies by Wednesday.

AVIATION.../Until 00Z Sunday/...The northern half of the panhandle remains dominated by a northerly outflow pattern, though it is continuing to weaken. Therefore, expect continued VFR conditions for PASI & northward through the 24-hour TAF period. For the southern Panhandle, a weakening area of low pressure is slowly drifting eastward over their area, which will cause primarily scattered snow showers, which may reduce CIG & VIS conditions to the MVFR category range when they occur. Between these snow showers, flight conditions will be as high as the VFR category. Generally, conditions will gradually improve to the VFR category range as the low continues to weaken & push through the area as time progresses closer to the end of the TAF timeframe. SFC winds will remain a bit breezy out of the north for the extreme northern panhandle, including the Lynn Canal / PAGY / PAHN area, with a continued general diminishing trend as the tight pressure gradient over that region continues to loosen up as the area of high pressure over the Canadian Yukon that has been causing the outflow weakens. Generally, those winds will subside by late tonight. Northeasterly LLWS of around 25 kt centered aloft at around 1.5 kft around the PAJN area looks to diminish this evening.

MARINE... Inner Channels...Outflow winds around 25 to 30 kt continue to blow down Lynn Canal and out of Taku Inlet Friday afternoon. These are expected to gradually diminish overnight as the low over the southern panhandle continues to decay. However, northern Lynn Canal is expected to maintain 25 kt sustained winds into Saturday morning. Freezing spray remains a possibility for many of the those northern channels especially at night. Otherwise most areas will be 20 kt or less mainly out of the north or east. Clarence Strait is the exception with SE winds continuing through this evening before starting to switch to a NW winds late tonight as the low disintegrates. The higher seas in the inner channels are still mainly focused on the outflow areas, especially the longer fetch areas of Lynn Canal and Stephens Passage where high winds blowing down the long linear channels built seas to 7 to 10 ft. Those seas are still expected to subside tonight as winds diminish.

Gulf Waters...Fairly quiet across the gulf with any winds over 20 kt mainly limited to the SE gulf near Prince of Wales and Dixon Entrance. That is expected to persist today before weakening tonight as the low weakens. Otherwise mostly N to NW 15 kt or less winds expected through Saturday across the gulf. Seas are generally low with 3 to 8 ft seas and little to no swell. A diminishing trend is expected for seas into the weekend. Most areas should be 5 ft or less by tonight and lasting into Sunday at least.

AJK WATCHES/WARNINGS/ADVISORIES

PUBLIC...Winter Weather Advisory until 10 AM AKDT Saturday for AKZ328-330- 332. MARINE...Small Craft Advisory for PKZ012-013-661.