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273
FXAK67 PAJK 211317
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
517 AM AKDT Fri Jul 21 2017

.SYNOPSIS...A high pressure ridge over the panhandle will slowly
weaken through Friday evening as an upper level low moves across
the southern gulf. A frontal band will move into the southern gulf
and southern panhandle on Friday then track northward over the
rest of the panhandle on Saturday.

&&

.SHORT TERM.../Friday through Saturday night/ Short range
forecast getting a little more active as a low that is heading
east across the southern gulf spins some frontal bands into the
panhandle. These bands are now looking to be coming in two waves.
Wave one, which is the windier of the two, will slam into the SE
gulf and southern panhandle today. Max winds expected this
afternoon and evening in the southern panhandle and SE gulf with
25 to 30 kt winds for marine areas and up to 30 mph gusts for land
areas. This frontal band rapidly weakens and shears apart as it
moves north eventually diminishing altogether over the central
panhandle Fri night.

Wave two, the wetter of the two, is following right on wave one`s
heels. The timing is so close that the brief break that the
southern panhandle may see between the first band and the second
Fri evening may be very short if it is noticeable at all. This
band will hold together much better then the first, potentially
spreading rain all the way up to Haines and Skagway by Sat
afternoon, before it starts to weaken Sat night. That was one of
the changes made for the current forecast was to increase the pops
in the northern inner channels to account for the band getting
farther north. Yakutat will largely remain dry as general flow
over the northern gulf coast remain mostly offshore.

Once this band passes, the southern panhandle is still not out of
the woods yet. Sat afternoon into Sat night features the upper
level low crossing the area bringing another round of rain in the
form of showers. Cold air aloft with this upper low also brings
the possibility of maybe seeing some lightning with some of these
showers. Guidance is suggesting upwards of a few hundred j/kg of
cape and LI values in the -1 to -3 range around the upper low Sat
afternoon and evening. Decided to put in some slight chance of
thunderstorm wording in the forecast for that time period. As the
Upper low starts to move into Canada remaining showers will start
to diminish late Sat night.

Short range guidance in good agreement on features for the most
part. Main changes largely confined to local effects using Nam and
GFS for guidance.

.LONG TERM.../Sunday through Friday as of 10 pm Thursday/
Sunday will begin with showers diminishing across the Panhandle
associated with the remnants of a weather front. Showers will
likely end by the afternoon hours for most of the Panhandle. As
the front diminishes a surface ridge of high pressure builds over
the eastern Gulf and Panhandle and persists through most of the
week. Winds over the Gulf will be relatively light and westerly,
while the inner channels will become more southerly. Significant
winds are not expected beyond the possibility of small craft level
winds in Northern Lynn Canal and Cross Sound. While this weather
pattern will keep conditions cloudy for most of the Panhandle,
chances of precipitation remain low in the extended forecast.

Most significant changes in the extended forecast were made
Sunday diminishing the shower activity across the Panhandle faster
than originally forecasted. This follows the trend models have
had for the past few days of speeding up this system. In addition,
the ridge over the northern Panhandle was intensified which lead
to an increase in winds within Lynn Canal and Haines and Skagway
area. Forecast confidence is average in the long term with a blend
of the NAM and GFS being used to handle Sunday and Monday and WPC
being the primary guidance Tuesday and beyond.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ036-041>043.
     Small Craft Advisory due to Seas for PKZ051-052.

&&

$$

EAL/Byrd

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