Area Forecast Discussion
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FXAK67 PAJK 221432
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKST Wed Feb 22 2017
-- Changed Discussion --As a weak system drops southeast, leaving the bulk
of the Panhandle with mostly clear skies and chilly temperatures,
another stronger one glides eastward across the Kodiak Island.
This one will set up a very weak overrunning event prompted by
warm air advection for coastal sections of Southeast Alaska, but
potentially farther inland as well. Tonight its energy gets
diverted to the southeast similar to the last, but weak lift will
maintain a chance of snow across the Panhandle overnight.
Visibility at Middleton Island is down to 3 miles at 13Z
suggesting snow bands may have pushed east of Cape Suckling yet
still lie well west of Yakutat. A surface low in the western gulf
will track east today. Unlike the last feature and its negative
tilt, this system`s structure comes in with hardly any tilt. And
the 00Z and 06Z NAM both tempt us with both a more northerly
track and more conducive southwesterlies in the low levels across
the Northern Panhandle. This would perhaps mean light
accumulations of snow over Pelican, Gustavus, Hoonah, Tenakee and
Juneau. But both ECMWF and GFS (both 00Z and 06Z versions)
maintain a more southerly track and quickly toss a few flurries
across these same areas while offering moderate confidence for
light snow with potential rain mixed in from Sitka south along
the coast. This brings up the epic conundrum for the north central
Panhandle of looking at each solution as a petal on a daisy: does
the snow fall, does the snow not? Rather than fight we simply
must present the forecast as is: we simply have little confidence
which explains the unsatisfactory 50 percent pops. But should
anything fall across this region, amounts will be light, and we
would be shocked if anyone received a couple of inches out of
this. An inch of snow, less, or nothing at all is more likely we
think. Any snow along the coast, and potentially anything that
makes it farther inland, will dissipate tonight as the deformation
band stretches south away from our area and weakens. Clouds will
generally persist most of the night.
The southern Panhandle will see effects delayed with this system,
as much of the area will experience sunny skies today. As the
approaching shortwave crosses the gulf this evening, the energy
split to the south will slow its progression, therefore, yielding
a rapid increase of clouds with a chance of snow/rain for Prince
of Wales Island and only a slight chance for the southern Inner
As the surface low moves into the central gulf this evening, 30 kt
easterlies will develop in the northern gulf with 25 to 30 kt
northwesterlies appearing in the central gulf south of the center.
Otherwise, seas will briefly rise to 8 feet across the northern
gulf this afternoon and tonight. Winds across the Panhandle look
to remain light but turn southerly ahead of the system this
afternoon before flipping back to northerly tonight.
EC/GFS offered the preferred track, but pops this afternoon and
evening were adjusted minimally to preserve uncertainty.
.LONG TERM...Somewhat quiet extended forecast today with an upper
ridge situated just to our west providing mainly offshore flow
over the panhandle. This pattern is broken once this weekend by a
moderately strong short wave moving through the ridge, and again
mid next week as a stronger trough suppresses the ridge to the
Main forecast concern is the trough that will be moving through
over the weekend (mainly Saturday) as forecast models are not
quite on the same page with it at this time. The main sticking
point appears to be on the strength of the system as the ECMWF and
CanadianNH are both around 9 mb stronger with the surface low
then the Nam and GFS. This is not the only difference between the
two camps. The ECMWF and Canadian are also showcasing a stronger
upper level jet on the western side of the trough and more cold
air advection based on 1000-500mb thickness forecasts. The result
at the surface is a noticeable difference in wind and precip
forecasts between the two camps (stronger winds and more precip in
the ECMWF and Canadian vs the Nam and GFS). Given the
differences, decided to stay the course for the weekend forecast
(which leans more toward the GFS at the moment) to see which way
the models lean in subsequent runs. Expecting 20 to 30 kt winds
out in the gulf, light snow for the northern panhandle with
accumulations of around 1 to 2 inches, and rain and snow for the
southern panhandle. These figures could ratchet up or down later
depending on which way future runs trend.
Otherwise, most of the extended forecast features mostly to partly
cloudy skies with winds mostly 20 kt or less. Temperatures will
likely range in the low 30 to low 40s for highs and 20s for lows.
Pattern change is possible for mid next week as a trough
suppresses the upper ridge to our west. This appears to bring in
some cooler air and a more active westerly flow pattern. Still too
early to get any details, but more precip and wind appears to be
the going trend for mid next week.
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-- Changed Discussion --PUBLIC...None.
MARINE...Small Craft Advisory for PKZ052.
Small Craft Advisory due to Seas for PKZ051.
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