Small Craft Advisory 791, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
332 PM AKST Fri Dec 16 2016

.SHORT TERM...Snow starting over the northern and central
panhandle as first short wave is crossing over the panhandle.
Solid westerly flow moving in warmer air, so lows for the night
are already occurring with temperatures steadily rising through
Saturday into the 30s. Next frontal boundary will cross over the
panhandle Saturday with another round of precip and warming air
mass. As temps increase will start a transitioning to a snow rain
mix, then eventually mostly rain, with the exception of the far
northern panhandle. Snow accumulation for most locations limited a
1 to 2 inches due to high water content. The far northern areas
and Hyder will receive 2 to 4 inches as colder air will stay in
place there. Rain on existing snow pack will result in slick
conditions with water ponding on surfaces.

Pressure gradient kept some higher easterly winds this afternoon
from outflow areas. With the next front southerly winds over the inner
channels will have a quick pick up to small craft. AK gulf winds
also pick up to westerly small craft through Saturday, in addition the
southwesterly swell brings wave heights up to 10 to 15 feet.

Models still in good agreement for synoptic patten. Used some high
res NAM to adjust winds up a bit as the front moves inland. Some
differences on precip timing so kept with the broad pop coverage.
Forecast confidence is average.

.LONG TERM...occluded front will move through much of the area Sat
night although it may get hung up over the far S area. Strong
occluded front will move into the area Sun. A low will set up over
the NW gulf Sun then weaken Mon. Another low will reach the NW
gulf around Tue..then slowly weaken there through late week. Used
mainly 12z NAM for Sat night-Sun evening, then used 12z GFS for
late Sun night and Mon. Went with WPC for Mon night onward.

The biggest concern for the weekend will be potential for heavy
snow near Hyder. Deep layer onshore flow will overrun the colder
airmass there. The big question mark will be whether the cold air
will hang around during entire Sat night-Sun night period. Models
often run arctic air out too quickly in Hyder and think this will
be the case again. Looking like an 18-24 inch snowfall for Hyder
from Sat evening through Sun evening. Decided to issue a winter
storm watch for them during Sat evening through Sun evening. There
is potential for significant snow at higher elevations of the far
N panhandle Sun into Sun evening. Later shifts may need to issue
snow headlines for that area.

Otherwise wind and rain will increase over the area Sun. Expecting
gale to storm force winds over the gulf with sca to gale force
winds over inner channels. May need strong wind headlines for much
of the land areas Sun as well. Temps will likely not fall much Sat
night, and may in fact rise gradually overnight Sat into Sun
morning.

Will continue to have shortwaves aloft moving across the area
during much of next week, which will keep area fairly wet. Model
timing differs on these so difficult to tell when any significant
breaks in precip will occur until late in the week when much of
the upper level energy will shift off to the E. This may also
allow some cooler air to move back in. Could see some snow during
the last part of the precip during late week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Storm Watch from Saturday evening through Sunday evening
     for AKZ029.
MARINE...Small Craft Advisory for PKZ012-013-031-033>036-041>043-051-052.
     Small Craft Advisory due to Seas for PKZ022-053.
&&

PRB/RWT

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