Small Craft Advisory 124, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
413 PM AKST Wed Mar 1 2017

.SHORT TERM...The words, "inconsistencies in the track of a low
bringing impactful weather to the Panhandle," do not radiate
confidence. But as we close in on decision time, we follow the
ECMWF/GFS/GEM track of the low taking moving it relatively quickly
up the coast late tonight just offshore of Baranof Island and then
wobbling it westward out to sea not very quickly into Thursday.
The NAM still has great attraction for Baranof Island and thus
brings it inland in a somewhat weaker state.

Precipitation will spread well ahead of the system this evening
and overnight to envelop nearly the entire Panhandle by morning.
It will generally start as snow but then change over or mix with
rain very quickly across the southern Panhandle. The warm, moist air
will surge northward eventually across Baranof Island and the
zone 26 area. Some late observations like Stewart, Canada indicate
some concern that snow may begin earlier and perhaps intensify
more rapidly across particularly zone 26. They are now down to 1/4
mile in a heavy snow band. We have issued a new winter weather
advisory for the possibility of 2 to 6 inches through 6 AM
Thursday morning. A rain mix will limit accumulations at the end
of the event. Should a rain changeover not occur, snow amounts
will likely be much greater, especially in Petersburg. An SPS
covers the rain over snow event which will have hazardous impacts
on an area unaccustomed to such a heavy snow pack.

Going farther north, an easier case for winter storm warnings can
be made for Pelican and Hoonah, where they easily verified the
last event from this morning. Juneau, because of the mountains and
the difference in model solutions provides once again a tougher
case. But given verification in snow amounts that occurred around
Downtown Juneau, but not in the valley/airport areas, we feel the
stronger dynamics of this system (given a closed upper low) will
be enough to counter any offshore flow at low levels. Should the
snow occur, the zone of greatest lift will occur along the Polar
front draped across the Icy Strait corridor. Should low level
winds veer back toward the southeast or east, available qpf will
be more limited and snow amounts will not materialize. Overall, we
expect 4 to 10 inches in this area. The winter storm warning
begins at midnight and lasts through 6 PM. We think the greatest
threat for Juneau will occur after 6 AM, but wanted to lump the
warnings together for potential error in timing. A winter weather
advisory was issued for Gustavus for the same reasons.

Finally, winds were fine-tuned and reduced in general across much
of the Panhandle. We keep the strong winds in Skagway but push
them back tonight as the strongest cold air advection will take
place. We have also limited wind speeds through Lynn Canal to 35
kt later tonight. We cannot argue with storm force easterlies in
Cross Sound as the low passes farther west.

GFS and ECMWF were used for edits. Forecast confidence just above
moderate for the snow events.

.LONG TERM...The low discussed above will remain over the NE gulf
Thursday night with gale force winds. Precip will become more
showery and intermittent through the evening as the low starts to
weaken. By Friday morning offshore flow on the north side of the
low will have diminished showers to scattered or less from Icy
Strait/Juneau north. The low will track south across the eastern
gulf through Friday evening and take the rest of the showers with
it.

High pressure to the north will cause winds to shift out of the
north everywhere as the low moves south. Dry, cooler, northerly
outflow looks to be the prevailing weather condition through the
weekend. Currently have many outflow areas with around 40-50mph
gusts. This will cause areas of blowing snow across the northern
half of the panhandle, since most places have had some snow this
week. There are some signs of precip over the southern panhandle
extending north from an inverted trough mid next week, but models
do not fully agree on this idea...and the dry outflow tends to
win out in these situations.

Most updates today were limited to the Thursday night/Friday
timeframe since models shifted the low center more west into the
gulf. Used the GFS, ECMWF and Canadian models since the NAM was an
outlier. Forecast confidence is average.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 6 AM AKST Thursday for AKZ026.
     Winter Storm Warning from midnight tonight to 6 PM AKST Thursday
     for AKZ021-022-025.
     Strong Wind from 3 AM AKST Thursday through late tonight for
     AKZ018-023.
     Winter Weather Advisory from midnight tonight to 6 PM AKST
     Thursday for AKZ020.
     Winter Weather Advisory until 6 PM AKST Thursday for AKZ029.
MARINE...Storm Warning for PKZ022.
     Gale Warning for PKZ012-021-036-041>043-051>053.
     Small Craft Advisory for PKZ011-013-031-033>035.
&&

JWA/Ferrin

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