Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 231319 CCA
Southeast Alaska Forecast Discussion...CORRECTED
National Weather Service Juneau AK
519 AM AKDT Sun Apr 23 2017
.SYNOPSIS...A weak front will bring a chance of precipitation to
SE AK this afternoon into Mon as high pressure over Canada
weakens. Upper level pattern becomes more onshore by mid week with
cooler temperatures and increased chances of precipitation for the
latter half of the week.
.SHORT TERM...Sunday through Mon night...Surface analysis and
satellite imagery depict a weak surface low W of Haida Gwaii early
this morning with a stronger low over the SW gulf. Models in good
agreement with the eastern low filling as it drifts NW. This will
push a weak surface front/trough into the southern panhandle this
afternoon and progress N overnight into Mon. The result will be
increased sky cover across the region with a chance of rain
increasing from S to N. Although NAEFS continues to prog temps 1-2
standard deviations above normal, increased sky cover will result
in temps a few degrees cooler than Sat. This trend continues Mon
as flow begins to shift more onshore in response to upper ridge
over W Canada becoming less negatively tilted.
NAM/ECMWF used for minimal changes with continued good forecast
.LONG TERM.../Tuesday morning through Saturday/ There is not much
change in the overall synoptic pattern through next week. The
polar jet will remain over the central Pacific and this will keep
the storm track south of the forecast area through mid week. There
will be a stronger low pressure system that will lift north out
of the north Pacific on Wednesday and move into the eastern gulf.
There are some differences with the track of this low but the
latest few model runs seem to be picking up on this feature. As
the low slowly lifts northeast through Thursday the threat of
precip will increase for the southern half of the forecast area.
The northern areas right now will see a chance of rain. For late
week into the early next weekend there is increased onshore flow
from the southwest and with that a chance of rain with cloudy
skies seems likely.
Wind wise...the inner channels will see relatively light winds
from the north through Wednesday night with weak northernly
pressure gradient. As the low moves into the eastern gulf winds
will increase to 20 kt over marine waters with 15 mph over land
from Fredrick Sound south. The winds will come around to the
south late in the week as a ridge builds over the northern panhandle
as the low moves into Canada on Friday.
Overall there is average forecaster confidence for Tuesday and
Wednesday but lower confidence after that due to the differences
with the low moving out of the north Pacific and spread in the
ensembles. Changes in the long term were modified using the 00z
Nam and 12z EC through day 4 then WPC for late in the week into
.MARINE...SEly swell will continue to subside today with small
craft for seas diminishing from SE-NW over the gulf today.
Over the inside, the strongest gradient will remain over the N
channels today with 20 kt expected for N Lynn and Cross Sound this
morning before diminishing this afternoon. Weaker gradient
expected Mon as front weakens over the western gulf and high
pressure across northwest Canada subsides. This will result in
diurnally driven winds remaining below 20 kt Mon.
MARINE...Small Craft Advisory due to Seas for PKZ041>043-051-052.
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