Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 100046
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
346 PM AKST Fri Dec 9 2016
.SHORT TERM...Arctic high pressure will persist over NW Canada
through Sat. E-W oriented upper trof will move S across the area
tonight and Sat. Used blend of the 12z GFS/NAM to try and get
best representation of the pressure gradient along the mountains
and over the gulf.
Main forecast concerns will be winds, temps, and hazards related
to both. The upper trof is helping to push in colder air from the
N and this should occur all the way to the southern area. This
will increase winds some tonight especially over the S. Expect
gales over much of the N half of the inner channels to continue
into Sat, with gale force outflow into the NE gulf as well. Temps
will be lowering enough tonight for increasing freezing spray
over the N and parts of the central inner channels, with N Lynn
Canal having the heaviest freezing spray. Locally, Taku winds
should be increasing early this evening with the increasing cold
advection, then they will likely diminish some Sat afternoon as
critical level is lost. Kept in the HWW for downtown Juneau and
Douglas. Kept strong wind headlines for PAGY/PAHN areas as well.
White Pass will see wind chill temps as low as 45 below late
tonight, and kept in the WCY for that area. Should be colder over
much of the area tonight by 5-10 degrees over Thu night lows. Sat
high temps should be about 5 degrees lower than today`s highs for
most of the area.
Kept the large seas going down the Lynn Canal/Chatham Strait
corridor due to swells generated by the gale force winds in Lynn
Canal, but did show this swell slowly diminishing as it enters
Chatham Strait and continues southward. Think highest seas will
occur over S Lynn Canal where longest uninterrupted fetch will
occur. Some larger swells will also affect Icy Strait mainly E of
Sisters Island and Stephens Passage N of Scull Island.
.LONG TERM...Very cold conditions and northerly winds will
continue into next week with freezing spray over numerous marine
zones and hazardous wind chill values along the Haines and
Klondike Highways. Little change in these conditions expected
through the coming week.
A weakening low pressure center vicinity Vancouver Island at the
start of the extended range forecast has a trough associated with
it that extends west into the south central gulf. This will
promote continued offshore flow, clear skies and low relative
humidities. Blowing snow also is expected and some near sea level
locations abutting higher terrain may observe what appears to be
flurries from this blowing snow as it makes its way off of the
Longer range models are indicating a surface high will build into
the southwestern gulf in the second half of the coming week.
Should this happen, the stiff offshore pressure gradient may relax
some and diminish wind speeds out of interior passes. However,
model agreement on this feature is not very good 5 days out into
the future and one model holds on to a lingering surface trough.
Current forecast reflects this trough and while forecast winds do
diminish in the second half of the long range forecast, they are
not as light as some models would indicate.
No PoP in sight, so enjoy the dry, sunny Winter scenery.
Used NAM for the early portion of the long range, followed by the
Canadian NH. latest WPC from Wednesday onward. Overall forecast
confidence is average.
PUBLIC...High Wind Warning until noon AKST Saturday for AKZ025.
Strong Wind through late tonight for AKZ019.
Strong Wind through late Saturday night for AKZ018.
Wind Chill Advisory until 11 AM AKST Monday for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
Gale Warning for PKZ012-013-021-022-031-043-051.
Small Craft Advisory for PKZ011-032>036-041-052-053.
Small Craft Advisory due to Seas for PKZ042.
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