Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 272218
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
218 PM AKDT WED JUL 27 2016
.SHORT TERM...WV imagery showed a midlevel impulse ejecting
northeastward across the gulf during Wednesday afternoon. Strong
ascent downstream from this feature, combined with increasing
southerly moisture flux, is aiding in the development of moderate
to heavy rainfall over the northern half of the panhandle. Model
guidance shows the rain persisting through Wednesday night...and
then subsiding to light showery activity during Thursday. In
addition, modest destabilization is forecast to occur close to the
upper disturbance, which will support a slight chance of
thunderstorms tonight over marine zones 51 and 52, as well as land
areas west of Yakutat.
Meanwhile, a compact surface low will linger over the northern
gulf during the next 24 hours. As a result, small craft wind
speeds will continue over the outer waters during most of the
night...eventually becoming confined to zone 52 during Thursday as
a second boundary layer wind maxima rotates northward into the
area. Over the inner channels, sustained southerly winds from
15-20 kt are probable during the night...and then subsiding by
Thursday afternoon. The one exception will be Northern Lynn Canal,
where speeds to 20 kt will continue into the afternoon as the
pressure gradient tightens in response to pressure falls over the
Yukon. Gusty south-southwesterly winds will also develop in
Skagway during Thursday.
Previous forecast appeared to be on track. Minor changes were made
using a blend of coarse and hi-res guidance.
.LONG TERM...Weakening low and upper trof will move across the
area Thu night through Fri night. Weak upper ridge should move
across the area from the west Sat-Sun. After that, looks like an
upper low will move across the gulf and close to the area for
early next week, but the models differ on handling this feature
so confidence in forecast lowers somewhat next week.
With the weakening low/trof coming in for Thu night-Fri
night, will have some showers continuing, but they will begin to
diminish from the northwest late Fri and Fri night as system moves
further inland. The weak ridge will help further diminish shower
activity over the weekend but there will be some onshore flow in
lower levels so clouds and isolated showers will probably remain
especially at higher elevations. The precip threat may increase
again early next week due to upper low, but due to model
differences, not going for above chance POPs at this point.
Did nudge some max temps upward a bit for Sun-Wed based on model
trends. MOS was suggesting even higher temps by a few more
degrees, but this will depend on how much cloud cover and precip
is around with the upper low.
.HYDROLOGY...Moderate to heavy rainfall will continue across the
northern half of the panhandle Wednesday night, and then subside
during Thursday. Area streams, rivers, and lakes will experience
rising water levels as a result...including the Taiya River near
Skagway, which is forecast to reach moderate flood stage during
Wednesday night. Refer to the latest flood warning statement for
PUBLIC...Flood Warning for AKZ018 until 1 AM Fri.
MARINE...Gale Warning for PKZ052.
Small Craft Advisory for PKZ022-042-043-051.
Small Craft Advisory due to Seas for PKZ053.
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