Small Craft Advisory 404, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
326 PM AKDT THU JUN 2 2016

.SHORT TERM...A weak shortwave lifting north across the panhandle
will bring a period of light rainfall tonight. However, the main
weather feature over the next 24 hours will be a quick moving
compact low lifting into the eastern gulf on Friday before
weakening into an open trough late Friday afternoon. An
anomalously strong 130 kt upper level jet for this time of year
will provide ample support for development of the low reaching a
minimum of around 992 mb early Friday. The system will then
weaken as it moves into the eastern gulf with upper level support
remaining to the south. Behind the low pressure system, a ridge of
high pressure will rapidly build from the south Friday afternoon.

The quick moving nature of this system combined with a 50 kt low
level jet will result in gusts increasing to 45 mph late tonight
and Friday for the southern panhandle. Winds will remain gusty on
the backside of the system as they shift to the southwest and the
second wrap pushes inland Friday afternoon. Small craft to gale
force winds will also occur over the southern Inner Channels.
Winds in the far northern areas will be light as the pressure
gradient parallels the north-south oriented channels. Ample lift
and precipitable water values around 1-2 standard deviations above
normal will bring a period of moderate rainfall which will spread
northward through the day reaching the northern panhandle late
Friday morning. Rainfall totals will be limited by the fact that
the system is moving so quickly. Do not expect any hydro issues.
One forecast issue was determining when the wind shift to south
would happen over the northern panhandle. After conferring with
the long term forecaster, decided to keep light northerlies
through late Friday afternoon before flipping winds to the south
Friday evening.

Used mainly Hi-Res model guidance for updates to the inherited
forecast. Forecaster confidence is above average on a wet and
windy Friday across Southeast Alaska.

.LONG TERM.../Friday night through Thursday/ First 24 hours of
the long range period is mainly dominated by a strong, for this
time of year, low plowing nw through the eastern gulf. The low's
proximity to the outer coast will lead to wet and windy
conditions Fri night into Sat. A strong SW low level jet on the
southern side of the low will cause the light northerly winds that
were in the inner channel in the short range to rapidly switch to
south and increase to 25 to 30 kt fri night as the low moves nw.
This increase in the winds will be rather quick as not only will
the low level jet increase winds a ridge will be building in
behind the low increasing southerly pressure gradients as well.
The possibility of gale force winds for inner channel marine
areas and strong wind gusts for land areas (mainly juneau, skagway
and along lynn canal) also exists but decided to remain just below
these thresholds at this time. This increase in winds across the
inner channels was the main change in the long range over the
previous forecast.

Otherwise, rain continues to be the other concern through the
weekend. The rain from this strong low will be moderate to heavy
but will also move nw through the panhandle rather quickly
dropping only around an inch or less of rain in any given area.
There will then be a brief break late Sat into Sun before a second
weaker low approaches from the SW. More rain is expected out of
this for Sun afternoon into Sun night but intensity wise it will
be light. Forecast quiets down into next week as main jet stream
get directed farther south as the west coast ridge flattens. Some
weak waves may still bring light rain to the area from time to
time but timing of these individual waves is still up in the air
at the moment.

Long range models were in good agreement through the first half of
the weekend. Strong low was well represented and agree upon by the
various models leading to the increasing of wind for the inner
channels Fri night into Sat. Model agreement starts to suffer into
Sun as scenarios for the next weak low to affect the panhandle
range from Cross sound to Prince of Wales island on where it will
come inland. Thought they all agree on the panhandle south of
yakutat being wet as the low comes inland. Agreement becomes worse
after that though the general trend continues to be drier through
at least Thu. NAM and GFS were used for guidance through the
weekend and WPC for next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...STRONG WIND from Friday morning through Friday afternoon for
     AKZ027.
     STRONG WIND from Friday morning through Friday afternoon for
     AKZ028.
MARINE...Gale Warning for PKZ036.
     Small Craft Advisory for PKZ022-033>035-041>043.
     Small Craft Advisory due to Seas for PKZ051-052.
&&

TPS/EAL

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