Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
246 PM akdt sun Aug 30 2015
Short term...quick developing low this morning has raced
northeast into the central Panhandle and has started to fill as it
moves across to British Columbia. A low over the northeast Gulf
will continue along with a trough across the northern Panhandle to
a low in the southwestern northwest territories.
The band of heavier rains along the frontal boundary pushes east
over the southeast portions of the Panhandle and into British
Columbia by early evening. Open cell showers in the flow pattern
headed to southern half of the Panhandle tonight and early Monday.
Clusters of showers more over the northeast Gulf from about Sitka
There is a fair sized cold pool aloft over the eastern portion of
the Gulf. This is adding to the instability and is allowing for a
slight chance of better convection. East of 140 roughly and
pushing into Prince of Wales Island.
Still some locally gusty winds West Coast of Prince of Wales
Island and along the Inner Channels south of Frederick Sound but
the winds are subsiding as the low weakens and pushes into
British Columbia this evening.
Only minimal changes today as solutions seemed to be good through
Monday. Confidence was above average for the forecast period.
Long term...upper disturbance located this afternoon over western
portions of interior Alaska is forecast to progress southeast across the
central/eastern Gulf Monday night through Tuesday. Ascent and cape will be
maximized downstream from this feature resulting in a slight
chance of thunderstorms over the southeastern Gulf and southern Panhandle Monday
night. Shower coverage will diminish north of the disturbance over the
northern Panhandle Tuesday morning...and likewise for the southern Panhandle Tuesday
night as the upper wave moves southeast away from the region.
A trough of low pressure is forecast to extend northwest across the southern
Panhandle and eastern Gulf Tuesday night through Wednesday. This feature combined
with high pressure over the Yukon will yield an offshore flow
regime for much of the region. The pressure gradient is forecast
to become particularly tight over Lynn Canal...with small craft
to possible gale strength nlys expected as a result Monday night
through Wednesday afternoon. In addition...the relatively long duration
of strong nlys combined with a long fetch down Lynn Canal will aid
in enhancing wave heights. At this time...a conservative 7 feet maximum sea
height was estimated based on 25 knots winds lasting 40 hours over a
fetch of 50 nm.
Wednesday and beyond...weak upper ridge is forecast to move across the
Gulf...while unremarkable features at the surface and aloft reside
over the Panhandle. Large diurnal temperature swings are
anticipated with this pattern due to potential breaks in cloud
cover. Model guidance is coming into marginally better agreement
regarding the potential for a wetter pattern next weekend.
However...significant spread is still evident in the evolution of
Inherited pressure grids were nudged toward the 12z European model (ecmwf) through
Wednesday...and then wpc thereafter. Only minor changes were made to
pop and quantitative precipitation forecast...most significant noted toward the end of the long
term period due to a blend with latest wpc guidance. Wave heights
over Lynn Canal were manually adjusted upwards per reasoning
public...strong wind until 4 PM akdt this afternoon for akz023-026>028.
Marine...Gale Warning for pkz033>036-041-042.
Small Craft Advisory for pkz012-022-031-032-043-051>053.
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