Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 231432
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKST Thu Feb 23 2017
.SHORT TERM...A weak system in the eastern Gulf of Alaska
resulted in a thick dusting of snow, around a half inch or less
over the Juneau area last night, and probably Skagway, Gustavus,
Hoonah, Tenakee, Angoon, and Sitka as well. If one could describe
the bands of very light snow ever as "intense," one could say the
heaviest period occurred late yesterday evening. The line
separating cloudy from clear skies lies across the Icy
Strait/Point Retreat corridor as of 4 AM. We fully expect that as
a deformation slides south and east, that this line will erode
more and more from the north through the day. Likewise, flurries
in Juneau and Angoon will end soon. Some fog briefly occurred at
Gustavus as the stratus dissipated, and repeat scenarios may occur
briefly this morning, across other communities that received
fresh snow overnight, but we do not think this will be impactful.
Therefore we omitted even patchy fog.
From Petersburg south, communities have experienced a mix of
clouds and clear skies, but generally more hit or miss than the
steady organized clouds of the north. As the deformation band
passes over this region this morning, we still think there is a
slight of light snow across Prince of Wales Island, Ketchikan, and
Metlakatla this morning. But any possibility of snow moves east by
18Z. Any snow will that does fall will hardly amount to a dusting.
A ridge aloft steadily builds over the Gulf and into the Panhandle
through tonight. This induces a stronger inverted trough at the
surface through the southern Panhandle. Thus northwesterlies
offshore will strengthen to 25 kt tonight. Likewise Stephens
Passage and potentially Clarence Strait will experience increases
as well. The building surface ridge also will swell seas to 8 to
9 feet later today into tonight across the eastern gulf.
Models indicate some mid to high level cloudiness dropping south
across the northern Panhandle this afternoon and tonight, but we
are not convinced that skies will be opaque. We mainly represent
skies as partly cloudy through the period.
NAM products were used as guidance where adjustments were made,
but few were needed.
.LONG TERM...Strong upper level ridge over the western gulf will
persist into early next week producing mainly north or
northwesterly flow over the panhandle. The result of which is a
rather dry and quiet forecast for the most part with one
exception. That exception is the moderate strength trough that
will be moving through the ridge Fri night into early Sat.
Long range models are getting better at fleshing that trough out.
The issues on strength of the system that were apparent between
forecast models 24 hours ago has settled out with a consensus
resting somewhere in the middle of the range at around 1016 mb.
Progression of the system through the area has also trended
toward faster with the trough taking most of the precip out of the
area by late Sat afternoon. All in all, This trough is looking
like it will be a quick hitter with enough cold air around that
the central and northern inner channels at least will see some
snow out of it. Outer coast and southern panhandle will be a
little more tricky for ptype due to temps expected in the mid to
upper 30s at times in those areas so primarily went with a mix.
Snow accumulations are expected to be up to 2 inches for the most
part where it does snow.
Pattern change in the works for mid next week as the upstream
ridge gets suppressed by a strong shot of cold air from Siberia.
The developing cold trough looks to tilt in a positive direction
toward late week orientated its axis just to our NW with a
embedded upper low lodged somewhere in the western half of the
gulf, though the exact structure has been shifting for the last
few days. The overall trend is a return to onshore flow for most
of the area with some precip possible for mid next week and
MARINE...Small Craft Advisory for PKZ041-042.
Small Craft Advisory due to Seas for PKZ043.
Visit us at http://www.weather.gov/Juneau