Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
543 am akdt Monday Sep 22 2014
Short term...on this last day of Summer Southeast Alaska is
cleaning up after a fast moving low moved north over the eastern
half of the Gulf of Alaska and inland to British Columbia. With
the strong gusty winds from the frontal band and low yesterday
pulling way and subsiding the last of the strong wind headlines
have ended and marine winds are dropping below small craft levels
through Monday. Residual swells are still impacting the coastal
water however they too will be subsiding.
Expect a weak ridge of high pressure of the Panhandle will be
lifting northeast into British Columbia through the day
Monday..this is partially in response to a strong vertically
stacked low about 600 nm southwest of haida gwaii that will be
moving slowly to the east through Monday night. The jet stream
will be south of this stacked features so Southeast Alaska will be
out of the active weather pattern now for a few days.
Colder air behind the frontal band and upper level trough are
allowing the development of shallow convective cells over the
eastern Gulf of Alaska and the northeastern Gulf Coast. Satellite
detection of the lightning activity has most of it along the coast
between caper fairweather and Icy Bay with cluster of cells near
the remains of the low that did not manage to clear the Coast
Mountains. Am expecting the isolated thunderstorms to persist
through today and work there ways south along the outer coast
towards the Prince of Wales Island. This afternoon. A few
thunderstorms may persist in the northeast Gulf Coast into the
Over all am expecting shower active to taper off through Monday
night starting over the northern sections and spread southward
with with the drier weather. Could see a few pockets of fog
tonight ... over the north but would like to see definite
clearing of cloud cover before I start to spread it into forecast
Long term...upper air pattern through much of the upcoming work
week will be dominated by a progressive northern stream over interior
Alaska and northwestern Canada...and a closed upper low drifting northward over the
northestern Pacific toward haida gwaii. Model guidance shows bands of deeper
moisture spreading northward from the closed low...which enter the southern
Panhandle by Wednesday morning...and eventually spread into the central
Panhandle on Thursday. Due to low-level offshore winds /forced by high
pressure over the Yukon and a surface low SW of haida gwaii/...as
well as generally weak forcing for ascent...rain will be
light...with highest probability of precipitation expected over southern areas due to
relatively Richer moisture.
Meanwhile...a deep-layer of dry air will develop over the northern
half of the County Warning Area Tuesday night through Thursday. This will favor mainly
clear skies and a large diurnal swing in temperatures. Model
guidance indicates low temperatures for Yakutat could fall into
the low 30s during this time period. However...northeasterly downslope
winds are currently expected to be fairly strong...which would
promote greater boundary layer mixing. Due to this
possibility...kept lows in the middle to upper 30s.
Otherwise...previously mentioned high to the north and low to the S
will yield northerly winds near small craft levels for many of the
northern/central inside waters.
The next Gulf cyclone then enters the forecast by the weekend
resulting in a pattern more conducive for rainfall across the
entire County Warning Area. Few changes to the previous forecast were necessary
with this long term package...the only exception being a reduction
in probability of precipitation/clouds over the northern County Warning Area through Thursday afternoon. Forecast
confidence is around average.
Hydrology...heavier rains across the northern Panhandle has
pushed the taiya river up into to minor flood stage overnight. The
river has crested at a shade over 17.0 feet and is on it way back
down. Other streams in the the region have reacted to the rains as
well but have remained with in their banks. Expect the Flood
Advisory the taiya to end Monday morning.
public...areal Flood Advisory until 10 am akdt this morning for akz018.
Marine...Small Craft Advisory for pkz012-013-021-022-051-052.
Small Craft Advisory due to seas for pkz041>043.
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