Small Craft Advisory 783, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
521 AM AKST Tue Dec 13 2016

.SHORT TERM...Upper level and surface high pressure over the
central gulf will continue the overall northerly flow across the
region today. Tonight the high will begin shifting to the SE and
flow will back more W-NWLY by Wednesday morning. This shift in
flow pattern will introduce more moisture into the atmosphere.

The high pressure over the gulf along with warmer air aloft caused
a marine layer to form yesterday evening. This deck of clouds has
hovered between 1500-3500ft and has been more aggressive moving
into the central panhandle this morning than expected. There will
be little to back these clouds off today and as flow aloft
becomes more westerly tonight, expect them to move inland a bit
more. Not expecting much in the way of precip out of this
feature, but a mid/upper level vort moving into the northern gulf tonight
would help to increase this possibility going into Wed. So, have
included a few flurries tonight along the central and northern
outer coast.

Temperatures have been one of the more difficult forecasts this
week. While 850mb temperatures have warmed, winds decreased and
did not allow for any mixing with the warmer air aloft. Therefore
we have seen continued well below normal highs and lows. The
winds backing and increasing along the outer coast tonight plus
more clouds would normally help those areas be a bit warmer than
they have been, but cloudy skies today will not allow for much,
if any solar heating.

Most adjustments to the forecast were made based on current
conditions, hi-res models and local effects.

.LONG TERM...Starting at 15Z Wed there is a weak shortwave with
slightly colder air digging into the Gulf with -32C at 500 HPa
that quickly exits our area early Thu morning. Addressed this wave
as chance or slight chance POPs as per the 13/03Z SREF and used
the 13/00Z ECMWF as the guide. The result was to mention
"flurries" for a few locations along the outer coast coordinated
with short term. As this shortwave kicks out, look for a new round
of outflow with clear cold dry and locally windy conditions.

As has been said on this discussion for a few days the next
challenge has been the real breakdown of the block and arctic air.
Another little upper disturbance will sneak by us on Friday and we
have mentions of clouds and snow. It takes until Saturday night -
early Sunday to kick out most of the strength of the upper ridge
into Canada for SW flow aloft. All 13/00Z ops models insist on
this but certainty is less than it seems. It is possible that
either the ridge will be slower to break down or the series of
approaching shortwaves happen to be weaker. Confidence is low on
timing, but have to fess up that the average position of the upper
ridge is history. If Monday temps are as warm as guidance sez,
there will be rain on this wonderful snowpack.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ042-043.
&&

Ferrin/JC

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