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000
FXAK67 PAJK 171444
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
644 AM AKDT Wed Oct 17 2018

.SYNOPSIS...Remnants of a long lasting atmospheric river event
will slowly dissipate on Wednesday with residual showers
persisting through the day. A low pressure system will begin to
rapidly develop over the northern Pacific Thursday, carrying a
band of storm force winds into the Gulf by late Thursday evening.
There is potential for strong winds Friday for the entirety of
the outer coast. Then another front will impact the Panhandle
Sunday.

&&

.SHORT TERM.../Wednesday and Thursday/ Wednesday is best
characterized as wet through the early afternoon hours with some
occasionally strong showers over the northern Panhandle.
Additionally the atmosphere remains unstable over a broad portion
of the northeast Gulf. This instability has been the source of a
fair number of thunderstorms through the overnight hours; the risk
for thunderstorms will persist through the morning hours.
Wednesday afternoon, the Panhandle will dry from south to north,
with decreasing clouds. There is potential for fog late tonight
for the southern Panhandle in areas under clearer skies and light
winds.

Thursday is rather uninteresting for the Panhandle with a short
period of dry weather persisting through the afternoon hours.
Late Thursday a very strong low pressure system will push into
the Gulf bringing storm force winds to the N central Gulf by late
Thursday night, with precipitation beginning once again for the
outer coast late in the night.

Overall minor adjustments were made to the short term forecast.
The risk of thunderstorms was increased over the NE Gulf early
today. Wind speed was decreased over the inner channels removing
the small craft advisories that were previously forecast this
morning. Overall forecast confidence is above average in the short
term.

.LONG TERM.../ Friday to Wednesday as of 10 pm Tuesday / Active
fall weather pattern will continue through early next week. Highly
amplified long wave trough in place over the AK Peninsula
extending well south into the subtropical NPAC. An impressive PV
max on the nose of a 130kt+ upper jet will eject northward into
the northern Gulf by early Friday. These upper features align well
with the low level frontal zone so expect the resultant low/front
to be quite intense. Ensemble IVT probabilities show 80-90%
likelihood of IVT in excess of 500 kg/m/s by mid day Friday which
matches most operational guidance depiction of a deep subtropical
moisture plume being drawn northward into the Panhandle. Another
period of heavy rainfall is likely Friday across much of the
Panhandle. Winds will also increase rapidly over the Gulf with
ensemble probs of storm force conditions over the northern Gulf
quite high for a 72 hr forecast. Models still differ on the
placement of any significant surface wave development on the front
for Friday, with the EC being the odd man in the collection of
models solutions. Stayed with the GFS to WPC solutions as the
support for the small changes in the extended. Bottom line, while
not explicitly in the forecast due to uncertainty at this time,
there is the potential for a strong fall wind storm on Friday for
parts of the Panhandle.

On the plus side, the persistent long wave ridging which has kept
much needed soaking rainfall out of the drought affected areas of
the southern Panhandle shows signs of becoming flatter and more
progressive. This would allow more significant rainfall to affect
even southern areas beginning on Friday and continuing into early
next week.

The tail end of the Day 6 to Day 8 forecast block has the hints
of yet another moist frontal system sweeping across the gulf from
the south as the main low tracks to the eastern Bering Sea. They
are also suggesting that there is at least one more wave on the
front that should roll up along coastal waters and either hit or
graze the southern panhandle. Will need to watch this system as
it develops and there should be a solid band of winds with it.
Long range forecast confidence is average.

&&

.AVIATION...Low conditions present this morning over much of the
Panhandle will lift late this morning and continue to improve
through the afternoon hours. Portions of the southern Panhandle
with lighter winds and clearer skies will favor fog development
once the sun sets this evening.

&&

.MARINE...A storm force low pressure system will rapidly develop
over the Gulf Thursday evening and raising seas to 15 to 20 feet
over the gulf by the late evening hours. Additionally storm force
winds are expected over northeast and central gulf between late
Thursday night and Friday morning. The front will rapidly push
through the inner channels on Friday creating the potential for
some brief gales and many small craft advisories.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ052.
     Small Craft Advisory due to Seas for PKZ022-041>043-051-053.

&&

$$

JB/DEL

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