Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Southeast Alaska forecast discussion 
National Weather Service Juneau Alaska
548 am akdt Wednesday Jun 3 2015

Short term...ridge axis has finally move east of the of Panhandle
area and the incoming weather system moving north into the central
Gulf Coast. Best chance of rain today will be from Yakutat west...
but should extend east as far as Sitka/Juneau with chance levels
to the east of there. A secondary and stronger feature is trailing
and will move into the northeast Gulf tonight. This system will be
carrying gale force winds with frontal band tonight. This second
system will also have the the best precipitation west of Yakutat
with Sitka - Juneau line being the main east Ward limit through
late Wednesday night. The Yakutat area could see 2 to 4 tenths
today and then start the heavier amounts again late tonight with a
quarter to half inch possible. Rainfall amounts over the rest of
the Panhandle should stay under a couple half inch for the next 24

Other than the gale force winds in the outer waters and some
small crafts developing over some of the Inner Channels. There
should not be any wind issues other than some turbulence or local
wind shear.

With the start of the rains the extended dry pattern is over the
time being with a few days of the wet expected for Southeast

Long term...upper low positioned S of Kodiak Island this morning
is forecast to move very little through Thursday. Meanwhile...a stronger
upper disturbance located S of the Aleutians will progress through
the base of the Kodiak low and then eject NE across the Gulf by
00z Friday. As this takes place...gale force front will weaken over
the eastern Gulf during Thursday afternoon...and will then be followed by a
trough of surface low pressure that will reach the coast of Southeast Alaska
late Thursday night. Episodes of moderate rainfall will accompany each
of these surface features...with rainfall intensity and duration
greatest for Yakutat/akz017. Ridge of surface high pressure is
then forecast to develop over the Panhandle on Friday aiding in a
tightening gradient that will support southerly small craft winds for
Lynn Canal.

South-southwesterly flow aloft will maintain moist onshore flow over the
Panhandle Friday through Sat favoring additional periods of rain.
Thereafter...model solutions diverge during sun...with
deterministic and ensemble GFS guidance producing a deep surface
cyclone that progresses northward over the Gulf...and the European model (ecmwf) showing
a weaker surface wave that skirts across the southeastern Gulf. Needless
to say...forecast confidence is not high for sun...but does
improve by Tuesday and Wednesday as multi-model solutions show a ridge of
surface high pressure redeveloping over the Gulf.

Inherited grids appeared to be in good shape...thus few changes
were made for this long term package. However...updated wave
height grids were limited significantly below maximum guidance values
over the outside waters sun through Tuesday...due to uncertainty in
the GFS forecast...which is used as input for the wave model.


Aviation...low ceilings will continue this morning for the
northeast Gulf Coast and into Prince of Wales Island and southern
Clarence Strait from the remains of the marine stratus however
that will be eroded away by the incoming weather front from the
south and southwest. Weather front is bring a fairly strong band
of wind so would not be surprised to see Yakutat and Sitka
locations report low level turbulence or wind shear tonight.


Hydrology...Glacier dam release of suicide basin into Mendenhall
Lake has ended and the lake levels are falling. There were no
reports of damages or flooding expected as the lake crested 1.5
feet below flood stage. An updated Special Weather Statement will be issued early
Wednesday morning.

Current forecasts for the taiya river has that river cresting
Thursday night/Friday morning at 16.2 feet and flood stage is 16.5
feet. This will be due to the rains expected to fall across the
area on Thursday over the northern Lynn Canal. The remainder of
rivers and streams in Southeast Alaska will rise with rain runoff
but should not cause any flooding issues with the event.


Ajk watches/warnings/advisories...
Marine...Gale Warning for pkz042-043-051-052.
Small Craft Advisory for pkz012-021-022-033-041-053.




Visit US at http://www.Weather.Gov/Juneau

National Weather Service Glossary of Abbreviations