Scientific Forecaster Discussion
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Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
311 PM akdt Mon Mar 27 2017
Short term...a complex mess of systems will be affecting the
area through Tue. A low over the east-central Gulf will move north-northwest and
dissipate along the north Gulf Coast by late this evening. Another low
will move NE across haida gwaii late tonight, then into central British Columbia
Tue. Yet another low will move north into the west Gulf Tue. The lows
will also have sfc trofs associated with them, mainly on S and east
sides. Used blend of the 12z GFS and NAM to handle things through
Main forecast concerns will be precip potential/ptype/amounts and
winds. As of 23z...rain was falling over most of the area, with
some snow still reported over the Haines/chilkat valley area. As
low moves past area to the west tonight, it will sweep a trof through
the area and precip should become showery and diminish over the north
and central Panhandle. The far S will keep some rain going as
next low brushes past them to their S overnight and Tue morning.
Once this low moves inland Tue afternoon precip should decrease
over the S. Over the NE Gulf Coast, they will be in and out of
precip through Tue with multiple lows/trofs affecting them. The
snow in the Haines/chilkat valley area should change to rain as
warmer air moves in this evening. Not expecting much more snowfall
there...possibly another inch or two.
Winds will be strongest near the multitude of lows and trofs. Up
to Small Craft Advisory level winds are expected near the main lows and trofs
moving through, with most of the stronger winds over the Gulf.
Will have some 20-25 kt east-southeast winds over much of the central and S
Inner Channels until trof moves through this evening. After that,
winds on Inner Channels will be in the 10-20 knots range although the
central Inner Channels may get fairly light overnight and Tue
morning with weak pressure gradient there.
Otherwise, think central Panhandle could get patchy fog overnight
as breaks in clouds occur and winds become light. It will be
rather short lived though as temps will rapidly warm Tue morning
in the late March sun.
Long term.../Tue night through Mon/ upper level trough over the
Alaska Peninsula will finally shift to the northeast while an upper
level ridge crosses in to the central Alaska Gulf by Wednesday
evening. As the ridge continues to track eastward over the
Panhandle the next significant low will move just south of the
Aleutian chain by Thursday. This upper low will then expand over
the western portion of the Alaska interior by Friday. After
that...uncertain on how it will eventually move.
At the surface, the low moving up the central Gulf will reach
Prince William Sound Tuesday evening with the associated front
tracking over the eastern Gulf and then the Panhandle through
Wednesday. Gulf winds pick up to Max small craft along the front
with potential gales. Precip from this front will mainly be
focused on the northeast Gulf and north central Panhandle.
Southwesterly flow starting a warming trend so expect more rain
than snow with only minor accumulations of a couple of inches for
the far north and at higher elevations. Surface ridge builds over
the Gulf behind the front for a drying trend starting late
Wednesday night into Thursday. This will be short lived.
The next major low will have moved south of the Aleutians by this
time with associated gale force front crossing into the central
Gulf. The front will reach the eastern Gulf then Panhandle early
Thursday evening into Friday morning. Winds will reach at least
gale force over the Gulf and potentially higher. Small craft
winds will increase over the Inner Channels. With the warm
southerly flow once again expect more rain than anything from this
front, but that rain may be heavy. The surface low will
eventually track eastward through the weekend followed by weak
New model runs were mostly in line with previous forecast
regarding position of the incoming system, a slight increase in
speed for the Thursday evening low/front. Mostly
refreshed/increased winds to a blend of GFS/European model (ecmwf) and increased
pops for the Thursday front. Due to southwesterly flow did not
drop pops off completely between systems but greatest chance for
dry/clear skies is over the southern Panhandle. More indications
of warmer overnight temps due to higher 850 mb temps/SW flow and
precip/cloud cover so also nudged up lows a few degrees. Forecast
confidence is average.
Marine...Small Craft Advisory for pkz022-034-036-043-051>053.
Small Craft Advisory due to seas for pkz041-042.