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FXAK67 PAJK 282248

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
248 PM AKDT Sun May 28 2017

.SHORT TERM.../Sunday night through Monday night/Models in fairly
good agreement and are all somewhat more aggressive with the
chance for precipitation associated with a weak front tomorrow.
PoP increased through Monday night as a result and this
represents one of the larger aspects of change in the latest
forecast. Another is cloud cover. Visible satellite imagery from
early this morning indicated a low marine deck moving north over
Hecate Strait and west of Haida Gwaii. The very shallow nature of
this cloud deck was revealed as the leading edge of the clouds
arrived at the southern tip of Haida Gwaii and became disrupted by
the land. Advance of this marine layer has been more rapid along
the western shore and those clouds are already over marine zone
41. Model guidance for these observed clouds was very poor today.
As a result, opted to use high resolution boundary layer relative
humidity as a proxy for clouds and this compared favorable to
observed clouds. Resulting forecast update features a marine layer
that penetrates into the southern inner channels and zones
tonight, along with areas of fog and drizzle. Potential is there
for the drizzle to make it as far north as Juneau by tomorrow
morning and then be replaced by a slight chance of rain in the

Marine winds remain on the light side at 15 kts or less for
tonight with up to 20 kts tomorrow for northern Lynn Canal and
Clarence Strait. Winds diminishing Monday night.

.LONG TERM.../Tuesday through Sunday as of 10 pm Saturday night/
Upper ridge will remain E of the area with upper low/trof sliding
E into the NE PAC through midweek, then remaining there into the
weekend. Still some model differences on individual shortwave
features which makes for a tricky forecast. Large scale pattern
would keep a threat for precip going over the area especially by
midweek. Ended up blending latest WPC guidance with previous which
nudged up POPs a bit. Also, decreased diurnal temp range somewhat
(lowered maxes and raised mins) due to expected cloud cover and
potential for precip, mainly from Wed onward. Models that came out
after WPC came in suggest an even higher threat for precip for
midweek into the weekend, so later shifts may need to bump up POPs
even more. None of the systems that will affect the area appear
to be too strong though the weekend, so would not expect more than
SCA level winds with them.


.AVIATION...A low marine layer will make for very low IMC
conditions overnight tonight and through at least mid morning
tomorrow for portions of the panhandle. No turb or LLWS expected
over the next 24 hours.


.AJK Watches/Warnings/Advisories...




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