Small Craft Advisory 57, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
355 PM AKST Tue Jan 24 2017

.SHORT TERM...A gale force low lies situated over the eastern gulf
as of this afternoon. As with yesterday's front, this one is
advecting more low level warm air over the panhandle from the
south. Snow level is already sufficiently high enough that
precipitation in the form of snow almost entirely limited to
higher elevations of the Haines and Klondike Highways. Winter
weather advisory for Haines and warning for Skagway remain in
effect, as QPF values for the present front are quite high. New
snow today is 3 inches at Haines Customs near the border and 5
inches at Skagway customs. PoP and QPF forecast for Tuesday night
unchanged. Updated Wednesday Using SREF, Canadian NH, and NAMDNG5
for PoP. QPF a blend of existing grids plus NAMDNG5.

Suspect overnight lows will occur early on, with temperatures
steady or slowly rising through the night. Main adjustments to
temperatures were to raise low for tonight up to afternoon values
being reported. Used primarily GFS MOS plus a little NAM MOS for
these adjustments.

Main changes to wind grids were to decrease wind speeds by 2 to 5
kts across the domain while preserving existing wind directions.
Even so, Have strong wind headlines for the central and southern
outer coast for this evening. Likewise for Haines and Juneau. Have
been waiting for a hint of wind at Skagway all day long. Reduced
those winds significantly as a result of calm wind obs all day.
Wind there finally picked up to about 15 mph by mid afternoon,
which is within the current forecast. However, this location will
need to be watched closely, since winds in Skagway are notorious
for changing abruptly and dramatically.

Overall forecast confidence is average.

.LONG TERM...Overall pattern remains warm and wet through at least
the weekend as an upper trough over the Bering Sea and a ridge
over western Canada remains in place. The panhandle is stuck in
the SW flow in between them with the Pacific storm track aimed
right at us.

Between Wed night and next weekend, there will be at least 3
separate strong fronts that will be targeting the area. The first
will be moving into the area from the SW on Thu bringing more
wind and rain. Gale force winds are expected for a large part of
the gulf and parts of the inner channels as the front moves
through. Gusts to 40 or 45 mph for land areas is also not out of
the question. Also with the strong warm air advection and many
areas already above freezing, ptype will remain rain for just
about everyone except for the higher elevations of the Klondike
and Haines Highways. Potential for another heavy snow event for
White Pass is there, though even there the strong warm air
advection could even make White pass warm up above freezing.

System number two comes up from the south for Thu night and this
one is looking like it will be the strongest of the bunch so far.
Long range models have gotten better at handling this system in
the last few runs though some issues remain. What is looking more
and more certain is that it will be a wind generator. 850 mb winds
over the southern panhandle Thu night are suggested to be around
75 to 80 kt which would likely result in gusts to 60 mph or more
at ground level. Kept winds a little lower than that at the moment
as models are just starting to settle on this system in the last
run or two. On the precip end, more strong warm air advection will
mean more rain for many areas.

System number three shows up Fri night right on the heels of the
Thu night system. Forecast confidence is terrible for this third
system with poor model agreement and run to run consistency. The
Models are insisting that there will be a system somewhere in the
eastern gulf Fri night but track and timing is up in the air.
Settled more on an ensemble approach to this system which has a
weaker low more toward the central gulf at the moment but with the
uncertainly later forecasts could trend closer to the outer coast
possibly resulting in higher winds. In any case, it appears that
this will be another strong system with another round of gale
force winds, warm air advection, and rain.

Into the late weekend and early next week operational and ensemble
models are showing increasing confidence on a drying and cooling
trend for the area as an upper ridge builds over the gulf and a
cooler air mass advances on the panhandle from the west. Timing is
an issue with the Gfs bringing the cold air in as early as Sat
night while the Canadian waits until Sun night. Decided to cool
temps down for next week and introduced some mentions of snow
toward the end of the weekend before the precip shuts off by
Monday. Used mainly WPC for extended periods.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 3 PM AKST this afternoon for AKZ027.
     Strong Wind from 6 PM AKST this evening through late tonight for
     AKZ027.
     Strong Wind until midnight AKST tonight for AKZ025.
     Strong Wind until 9 PM AKST this evening for AKZ023.
     Winter Weather Advisory until 9 AM AKST Wednesday for AKZ019.
     Strong Wind until midnight AKST tonight for AKZ019.
     Winter Storm Warning until 9 AM AKST Wednesday for AKZ018.
MARINE...Gale Warning for PKZ012-013-031>034-036-041>043-051.
     Small Craft Advisory for PKZ011-021-022-035-052-053.
&&

Fritsch/EAL

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