Area Forecast Discussion
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FXAK67 PAJK 141438

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
538 AM AKST Fri Dec 14 2018

.SHORT TERM...Weak low and trough over the northeast Gulf of
Alaska will spread showers into the northeast gulf coast as well
catching the norther coastal zones with some shower activity. The
early morning lightning detected by satellite west of Chichagof
Island should end by sunrise.

High pressure will continue to build over the eastern gulf and
panhandle region behind the through in the north gulf. The ridge
axis across the central panhandle cleared out some clouds which
allow patchy fog to develop and that may linger into the early
morning. Once the shower activity ends today on and north coast,
dry weather should continue into Saturday morning.

The ridge above is also aided by the large deep low moving into
the western Gulf of Alaska. Model solutions have the low center(s)
in the lower 960s for a depth. The frontal wraps about the large
low and the leading edge will move in from the southwest with
storm force winds of about 55 kt. Rain should reach the southern
panhandle Saturday morning, and then will lift northward into the
panhandle. Near the coast mountains with the easterly winds,
think precip will be hampered by downslope drying. Think there
will be a good east west gradient so expect those channels to howl
at near Gale force in the marine areas. Lynn Canal will start to
blow from the north into the low for the gulf. A mountain wave
event looks to be starting late Saturday afternoon for the
downtown Juneau and Douglas area so have issued a High Wind Watch.
The front will then move northward into the northern panhandle,
and this should result in a good overrunning snow event for the
northern Lynn Canal region. We pondered a watch for snow
accumulations for Saturday night, but have held off so far, and
will have next shift check the snow total potentials.

.LONG TERM.../Sunday through Friday night/...Extended range
forecast begins with a large, negatively tilted upper trough
which will move east to be over the Panhandle by Monday morning.
Model. Low level southerly jet will start out strong, particularly
along the outer coast, but will diminish significantly by Monday
afternoon. At the surface, a very large high end gale force low will
dominate the entire gulf. This system will track north towards
western Prince William Sound while weakening, dissipating over
the interior by Monday afternoon. Even as this low exists the
forecast area, another will be tracking northeast, to enter the
southeastern gulf Monday night. Model agreement at this point in
the long range forecast is below average, so no one deterministic
model was used. Instead, current forecast of this second low
reflects an ensemble approach to both pressure and wind. That
being said, if models remain consistent, it is likely that winds
over the eastern gulf will need to be increased to gale force. If
the track of the low shifts to the east, strong winds along the
southern outer coast are possible early Tuesday with gales in
Clarence Strait. WPC used beyond this point.

After a break in the precipitation on Friday, the first low will
have pushed a front into the Panhandle. Showers from this front
will remain over Southeast Alaska until the front associated with
the second low arrives from the south Monday night. In summary -
wet and/or snowy weather will persist through the upcoming week.
Overnight lows over the central and northern inner channels will
allow for accumulating snow with the best chance being Sunday
morning. Daytime highs will probably allow for a transition to
rain by Sunday afternoon everywhere but the far northern inner
channels - Haines, Skagway, and the highways. This may wind up
becoming an advisory event for those locations. Weak warm air
advection early in the week associated with the second front and
low will most likely result in a p-type of rain both day and
night for locations south of the Icy Strait corridor. By midweek,
the trend reverses with the rain/snow lines shifting south in the
overnight hours to Frederick Sound late in the week.

Used GFS for updates to the mid range wind forecast Sunday and
Sunday night. Net effect of this was to increase winds to 40-45
kts. Used the National Blend for updates to PoP Sunday through
Monday evening. WPC thereafter. Overall forecast confidence is


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind late tonight for AKZ027.
     High Wind Watch from Saturday afternoon through late Saturday
     night for AKZ025.
MARINE...Storm Warning for PKZ041.
     Gale Warning for PKZ042-043-051-052.
     Small Craft Advisory for PKZ022-033-036.
     Small Craft Advisory due to Seas for PKZ053.




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