Gale Warning 12, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
226 PM AKST Sat Jan 5 2019

.SHORT TERM...Outflow winds continue to be the main forecast
problem in the short term. A very cold airmass is currently
located over the Yukon, characterized by temperatures down into
the -30s at a few sites. The cold air has significant depth,
enough to make it over the Coast Mountains and this will lead to
strong outflow winds continuing and developing further south this
evening and overnight. Winds in Lynn Canal have slowly increase
today and are currently around 40kt. Some increase is expected
tonight as strong low level cold advection commences. With the
falling temperatures, vessel icing poses a significant risk and
thus went with a heavy freezing spray warning for tonight in Lynn
Canal. Dangerous wind chills will also develop along the Klondike
Highway tonight through Sunday morning. The depth and strength of
the cold advection, combined with a critical level near 500mb
late tonight and early Sunday will likely lead to strong winds
developing near downtown Juneau/Douglas. Cross barrier flow is
lacking a bit from what we would expect from a strong Taku Wind
event, but with the other ingredients in place, still think a few
gusts as high as 60 mph are likely and thus upgraded the High Wind
Watch to a warning through noon Sunday.

Cold temperatures will continue through Monday night, with Sunday
night likely being one of the coldest nights of the season so far.
Temperatures will likely approach 0F in many wind sheltered
locations of the northern Panhandle.

Guidance differs a bit on weak shortwave energy moving into the
northern and eastern Gulf on Monday/Monday night. Flow a H85-H7
turns onshore for a time, and with a very cold arctic airmass in
place, light snow will likely develop along the Gulf coast and
possibly the north central Panhandle. Still too many model
differences to pin down snow amounts but would not take too much
in the way of qpf to produce accumulating snow considering the
very cold low level thickness values.

.LONG TERM.../Monday through Saturday/...Cold conditions with
northerly and outflow winds will still be main weather impacts
for the start of the long range with potential pattern change
towards the end of the week and into the weekend.

Cold air mass over the Yukon and British Columbia remains in
place driving thermal outflow winds with pressure gradient
enhancement as another low moves just south of the panhandle
Monday. Expect low temps in the single digits for the
north/central panhandle and continued sunny skies. Hazards will
remain as small craft to gale force winds and freezing spray.
These winds will begin to diminish slightly as the surface low
fills Thursday into Friday thus removing the pressure gradient
element. There is a weak circulation setting up in the northeast
gulf which picks up low precip probability over the AK Gulf and
coastal panhandle, but low probability in the way of impactful
precip. But these small spinner can stall and drop some more
precip than expected. The question is how long will the cold air
remain in place and if and when precip begins to move in will an
over running snow event set up?

First off models in the long range have been...poor. Lots
of run to run inconsistencies and model differences. This is
possibly due to the building of a blocking mid level high mid
week then its dissipation, which often models then have
difficulty resolving upstream flow. There is more agreement with a
deep low moving in towards the Aleutians, but the trouble is with
cyclogenesis in the AK Gulf extending from this main low. Overall
looks like a shift to more southerly flow which would bring in a
warmer, moist airmass. GFS has been more aggressive with the
strength of the low but starting to trend the track more to the
west. Model spectrum spread indicating colder air staying in place
longer, but when comparing various MOS Guidance there may be more
of an erosion to the cold air before any precip moves in. In a
nutshell leaning more toward a pattern that would start as snow
but transition to rain rapidly. However, as stated before, models
in the long range are...poor, and thus low confidence. What is
likely is staying dry, cold and locally windy through the week
then change for the weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Warning from 6 PM this evening to noon AKST Sunday for
     AKZ025.
     Strong Wind through Sunday afternoon for AKZ019.
     Strong Wind from 6 PM AKST this evening through Sunday afternoon
     for AKZ018.
     Wind Chill Advisory from 9 PM this evening to noon AKST Sunday
     for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ012.
     Heavy Freezing Spray Warning for PKZ013.
     Gale Warning for PKZ012-013-031-033.
     Small Craft Advisory for PKZ022-032-034-036-041-042.

&&

DEL/PRB

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