High Wind Watch 9, NWS Juneau, AK

Southeast Alaska Forecast Discussion...Corrected
National Weather Service Juneau AK
242 PM AKDT Thu Nov 1 2018

.SHORT TERM.../ through Saturday / A mid 980 mb low is tracking
east across the central and eastern gulf Thursday afternoon, while
the associated frontal band has blown through the southern two
thirds of the panhandle and into Canada. The front is wrapping about
the low so the southern portion of the panhandle should expect the
rain to re-intensify Thursday evening and then weaken again as the
low passes through. Did not make much in way of changes through
tonight over the panhandle.

Friday afternoon the next frontal band is approaching the southern
panhandle. The various models are fine tuning their paths and
strengths, for now have settled on a more GFS centric choice with
the recent track record, and it had more of a middle of the road
timing as well. Rain and wind will begin Friday evening in the
southern panhandle then front will continue to spread inland. As a
result the north and northeast pressure gradients will be increasing
Friday night and into Saturday. Have increased winds through the
inner channels as well as the outflow winds that impact interior
passes like the Taku and Stikine River valleys. Based on the
forecast gradients from the latest model solutions this morning we
have issued a High Wind Watch for Saturday morning to evening for
the possibility of gusts of 60 mph to impact downtown Juneau and
Douglas in an outflow/(Taku) mountain wave event.

The area along Icy Strait to Juneau still looking like they may
pick up the first measurable snowfall either tonight or Friday
night, although indications now are hinting that Saturday night
could be a better chance of snow accumulations showing up. The
southern half the the panhandle will just see rain from these
fronts. Winter is not entirely here yet.

.LONG TERM.../As of Wednesday evening/ Not much has changed in the
low predictability of the long-term forecast. It has became second
nature during this October and now into November, that
predictability plummets three days out, very close to what we
generally term the long-term forecast period. This is precisely why
we may have considered letting the entire forecast ride for Saturday
and beyond.

Initially, the Canadian GEM, the GFS, and the NAM all fell in line
with a wave pressing northwestward along our shores in line with
a front on Saturday into Saturday night. In fact, the Wed 00Z
ECMWF from yesterday also agreed with this alignment. The Wed 12Z
ECMWF was the outlier as it kept the system well to the south.
However, new runs of the NAM and Canadian have all lined up with
the southern position of the latest ECMWF. So while confidence in
a wave, that we had not even indicated in the forecast before has
increased, confidence in its position is flaky. Late breaking
news appears now to indicate the Thu 00Z ECMWF has now moved it
back to a more northerly position, slightly bolstering our
changes. Now we must state why either of these positions is
important to the forecast.

A more southerly position may entrench the colder air mass a bit
more across the northern Panhandle given northerly winds in the
low levels. But perhaps more importantly, the precipitation may
fail to reach areas north of Angoon. But a northerly position,
would moisten the atmosphere across the northern Panhandle and
offer another shot of rain/snow over the north. While we kept
forecast temperatures in the middle to upper 30s for most areas,
we decided to change p-type across many northern areas to a mix
with some outright snow during the morning hours for
Haines/Skagway. While low level thickness values do not impress
for snow, and some of the models are indicating warmer surface
temperatures, the northerly flow and the overall dry atmosphere
concerns us sufficiently. Some higher res models indicate a
chilling of the lower atmosphere (850 mb) around the time of
precipitation onset. And nearly all models have a stark snow level
line right around the Icy Strait corridor with Juneau's snow
level either at 5000 feet or at zero, depending on the model you
believe. These values are an intimidating discrepancy to solve.
But too many models indicate very low snow levels, so we felt a
mix is more appropriate for these areas.

This will be another tricky forecast as the season of trick-or-
treat keeps treading on through November. What we can say is that
the southern and central Panhandle will likely to definitely see
more beneficial rain. Unfortunately, at this rate, we are merely
bringing rainfall rates through the calendar to something that
passes for normal around here. Finally, we did increase southeast
winds through the southern regions as the gradient increases with
the wave. Likewise, we increased northerly winds to small craft
through Lynn Canal and gap winds for Downtown Juneau.

The GFS 5-wave which gives us a very rough long-wave pattern to
follow for next week indicates a possible break in the persistent
precipitation sometime early next week, however, we have been
through this debate before and would prefer to see more than a
basic long-wave pattern to lower pops at this stage. We shall
continue with rain/precipitation in the forecast for the
foreseeable future across most sections of the Panhandle with a
general wind pattern indicating some sort of low in the gulf.

We used 18Z NAM, GFS, and 12Z Canadian GEM for edits to
Saturday/Saturday night and let Sunday beyond ride for now. Edits
were mainly done to p-type, wind, and pop/qpf.

&&

.AVIATION...Marginal flight conditions with ceiling of 1500 to
3000 feet over the southern half of the panhandle tonight then
improving Friday after the low passes. Gusty winds persisting at
lower levels in the north central panhandle through the early
evening are leading to so some turbulence near rough terrain and a
few local areas of wind shear. Expect the wind issues to subside by
late evening.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch from Saturday morning through Saturday
evening      for AKZ025.
     Strong Wind until 6 PM AKDT this evening for AKZ025.
     Strong Wind through late tonight for AKZ017.
MARINE...Gale Warning for PKZ012-013-022-043.
     Small Craft Advisory for PKZ021-031>033-041-042-051-053.
     Small Craft Advisory due to Seas for PKZ052.

&&

Bezenek/JWA

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