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FXAK67 PAJK 141540

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
640 AM AKST Thu Dec 14 2017

.SHORT TERM.../Thursday morning through Friday night/...Satellite
imagery early this morning is showing the colder high cloud tops
associated with the front oriented north- south and east of
Chatham Strait. Earlier this morning, Very gusty winds associated
with frontal passage were observed first over the southern zones,
then over Stephens Passage, the downtown Juneau area, and then
finally, up into Lynn Canal. Most of the flow with this front in
from south to north, but easterly progress has increased overnight
and the very gusty winds at the surface are expected to subside
by mid morning. Gales over Clarence Strait and small craft winds
over the southern inner channels will diminish through the
morning. Winds over the far northern inner channels will increase
later this morning and remain at small craft levels through most
of the night. Strong winds are expected in Skagway and along the
Klondike Highway tonight. Over the gulf, post frontal winds will
shift southwesterly with a band of gale force winds moving north
across offshore zone 310 this morning and entering the coastal
marine zones west of Yakutat Bay by this afternoon. By Friday,
conditions calm down on the inside, but the next front, another
high end gale force event, will be entering the central gulf.
Gales will spread east over the coastal marine zones late Friday
night with small craft conditions over most of the inner channels.

As expected, heavy rain accompanied this front and the Juneau
forecast office recorded 0.69 inches of rain in just 3 hours
between 9 pm and midnight with a 24 hour total of 1.23 inches. The
Juneau airport recorded slightly more with 1.44 inches and Yakutat
recorded 2.22 inches. Panhandle creeks and streams have responded
accordingly and very early this morning Jordan Creek near Juneau
reached bankfull. Rain rates have tapered off a bit and the
current thinking is that Jordan Creek will crest before reaching
flood stage. Rain will transition to showers later today and
convective parameters indicate the potential for thunderstorms
late this afternoon and overnight over the eastern gulf and
portions of the outer coast. Showers will slowly taper off
overnight and through the day Friday. The gale force front headed
our way Friday night will bring more heavy rain to the panhandle
by the end of the short range period late Friday night.

Used NAM for updates to pressure. NAM and NAMDNG were used for
winds over the gulf and NAM Nest for the inner channels. PoP and
QPF from GFS. Temps nudged towards the bias corrected ECMWF.
Overall forecast confidence is average.

.LONG TERM.../Saturday through Wednesday/ As of 10pm
Wednesday...The extended forecast starts off with a strong front
over the eastern gulf and widespread rain over the panhandle.
Models are now indicating a barrier jet and elsewhere along the
front to have storm force winds. Have increased wind speeds with
this package up to gale 35-45kt for now since models are still
showing some differences on when the peak timing would be. Winds
aloft will have shifted to the SW which will increase rainfall
rates to heavy at times again and keep temps on the warm side.
Therefore any place that had started off as a mix or snow will be
all rain by Saturday morning.

The low looks to move inland near PWS Saturday afternoon and
precip will transition to showers across the panhandle, although
remaining wet due to persistent onshore flow. Temperatures aloft
will start to cool at this point however, so do have places over
the northern inner channels with snow mixed in Saturday night and
Sunday. Not expecting much accumulation with this snow, potential
is there for a few inches, but warm surface temperatures will
likely cause the snow to melt on contact to start and
significantly limit accumulations.

Sunday night into Monday a new low center will be over the north-
central gulf. This will help to keep showers going (mostly rain
during the day and some mixing/snow at night) across the region.
But as the low tracks S-SE through Monday, winds will turn out of
the north and offshore, causing decreasing POPs and cloud cover
from north to south. Meanwhile the upper level jet will also have
turned out of the north and draw down colder air across the
region. Models have come in line with the shift to north winds on
Monday/Tuesday, but the GFS and Canadian keep that going Wednesday
while the ECMWF has it breaking down already with a shift back to
the SE. Think that it will persist a bit longer, so have
increased northerly winds through the inner channels through mid
next week. All signs point to this "cool down" back to normal
December temperatures to not last and things warming back up
above normal levels beyond the long range period.

Models were in better agreement on the overall pattern for this
package. Preferred the GFS for most updates as it was in line
with the forecast from yesterday and other models came into better
agreement with its solution. Forecast confidence is average, but
lower for accumulating snow.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 6 AM AKST early this morning for AKZ027.
     Strong Wind from this evening through late tonight for AKZ018.
MARINE...Gale Warning for PKZ034-041>043-051-052.
     Small Craft Advisory for PKZ011>013-021-022-031>033-035-036.
     Small Craft Advisory due to Seas for PKZ053.




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