Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 241350
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
550 AM AKDT WED AUG 24 2016
.SHORT TERM...Damp morning for areas from Frederick Sound
northward as a weak trough lingers along Icy Strait. For the most
part the rain has been light with 0.10 inches or less in the last
12 hours. However, heavier rain has been observed along a line
stretching from Yakutat through Glacier Bay and into Juneau with
upward of 4 tenths of an inch measured in the last 12 hours in
these locations. Complicating the weather more is widespread low
ceilings and fog this morning. Several locations are reporting
ceilings of only a few hundred feet with visibilities ranging
anywhere from 6 miles to as low as a quarter mile at times. Only
the area around Clarence Strait and into Misty Fjords is seeing
partly cloudy skies.
Main forecast feature today is the building ridge over the SE gulf
and southern panhandle. This ridge will force the trough over Icy
Strait northward and weakening it at the same time. The overall
result is improving conditions over the northern inner channels
with slight chance to chance pops by this afternoon and drier
conditions further south. The ridge will then start to drift to
the west tonight further pushing the rain to the nw.
Overall forecast into tonight will mainly depend on which side of
the ridge you are on. The northern gulf coast will still be on
the western side of the ridge under southerly flow. Rain will
continue to be in the forecast for that area through tonight.
Expected rainfall amounts will be around 0.50 to 1 inch through
the next 24 hours with the heaviest rainfall west of Yakutat.
Meanwhile much of the rest of the panhandle will be on the east
side of the ridge axis by tonight. Under northwest flow most of
the inner channels will be dry but some clouds will linger as low
level moisture remains high, particularly in the north. Fog will
also likely make a return tonight as well with less mid level
Short range models were in good agreement for the next 24 hours.
Some minor disagreement on wind magnitudes in the SE gulf tonight.
Decided on going with GFS and Canadian-Reg for guidance today.
.LONG TERM...Upper ridge over the area will be flattened by a trof
moving through it Thu and Fri. Latest models in decent agreement
on timing of the trof passage through the area, and were very
close to timing in the previous forecast. Decided to leave most of
the forecast as is through the weekend although did make some
tweaks to temps and winds. Left next week forecast as is.
For Thu into Thu night, with trof moving through the area, will
see mainly wet weather across the north. Heaviest rain will be
along the northeast gulf coast. Did lower temps a bit over the
north Thu due to the rain. The south will probably have another
warm day Thu with more sunshine likely there. Tweaked temps upward
some over the south Thu especially the southern three zones. Did
tweak winds upward some over the gulf based on model trends out
For Fri and Fri night, the rain threat will begin to diminish
from the northwest as upper trof moves past. The upper ridge will
try to bounce back to the north but will likely do so more over
the far western gulf and southwest AK. This will put area under
northwest flow aloft by Fri night.
For the weekend, Sat is looking drier and warmer especially with
increased offshore flow in lower levels. Did nudge temps upward
some based on the 925 mb temps. They may need further raising if
the northerly low level flow can mix down easily. May need to
revisit cloud cover for at least Sat as well as a clearing trend
could occur more quickly than currently forecast. A complicating
factor though is another shortwave trof the models show moving
into the area Sat night, which could bring in more clouds at
least. By Sun into early next week, models begin to diverge on
evolution of upper pattern over southeast AK and the gulf so
confidence in the forecast begins to lower around Sun and
continues into early next week.
MARINE...Small Craft Advisory for PKZ041-052.
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