Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 242230
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
230 PM AKDT SUN JUL 24 2016
.SHORT TERM...Remnants of yesterdays low pressure system could
still be seen on visible satellite imagery this morning as a
circulation off of Cross Sound. The low remaining in tact helped
to keep easterly winds through Icy Strait most of the day, but
have now shifted to the SW as the flow pattern over the gulf
becomes dominant. Onshore flow across the region has kept showers
going today, mostly in places with west facing mountains
(Juneau), while downsloping is starting to cause some breaks in
places like Angoon. More breaks are expected overnight across the
south with showers becoming more scattered, so have included
patchy fog there. Have also adjusted highs over this area up
slightly for sunny breaks during the day tomorrow.
A ridge of high pressure will remain strong over the inner
channels this evening with small craft level winds through Lynn
Canal and Stephens Passage. The pressure gradient will start to
slacken overnight and allow winds to diminish. This weakening
trend will continue through Monday afternoon starting over the
southern panhandle and working northward through the day.
A system over south central Alaska will move into western gulf
and strengthen through Monday. This system is already causing rain
to move into the Yakutat area. Rain is expected to continue in
Yakutat as the system strengthens tomorrow. Moisture will be
drawn up into the eastern gulf by the broad low pressure on
Monday. Have introduced likely rain to POW Island during the late
Models were in good agreement through the next 24hrs. Used an
ensemble approach with an emphasis on the NAM12 and CanadianReg.
Forecast confidence is average, but slightly lower for how long
the showers will persist.
.LONG TERM...Model guidance shows a quasi-stationary upper low
positioned over the southwestern gulf through midweek. This will
place SERN AK under moist southwesterly flow aloft...with
precipitation becoming widespread and potentially moderate in
intensity during Tuesday as a midlevel impulse moves across the
region. A second disturbance follows a similar track Wednesday
night. Thereafter, the upper low is forecast to become mobile,
moving east across the gulf during Thursday, and then southeast
across the panhandle on Friday.
At the surface, a ridge of high pressure is forecast to be
positioned over the panhandle through most of the week, while low
pressure remains over the western gulf until Wednesday. Modest
southerlies will persist over the inner channels as a result,
while speeds approaching small craft thresholds are expected over
the outer waters. In addition, as low pressure drifts eastward
over the gulf Thursday night, seas to 11 feet are forecast to
spread to the eastern gulf.
Pressure grids were nudged toward WPC during the extended portion
of the long term period. Remainder of the grids were in pretty
good shape...followed WPC, ECMWF, and GFS guidance for additional
MARINE...Small Craft Advisory for PKZ012-031-052.
Small Craft Advisory due to Seas for PKZ022-041>043-051.
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