Gale Warning 44, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
319 PM AKST Wed Jan 25 2017

.SHORT TERM...Showers linger over the northern panhandle in the
wake of the most recent front to impact the area. Shower activity
will diminish through the night, but be replaced by stratiform
precipitation from the next front, currently forecast to spread
rain inland beginning late tonight. Several recent fronts have
each advected in warm low level air. Accordingly, snow levels have
been driven up such that accumulating snow is only expected near
White Pass. Even there, it may become a rain-snow mix on Thursday.
For now, have 2 to 4 inches accumulation in the forecast. Post
frontal stability parameters indicating the potential for isolated
thunderstorms over the gulf. Lightning detection over the
northern Pacific indicating thunderstorms in the post frontal
airmass as of this afternoon, so have included them in the marine
forecast for tomorrow.

Approaching front will be storm force west of Yakutat Bay, with
high end gales extending all the way down to the Dixon Entrance by
tomorrow morning. Also have gale warnings out for Cross Sound, Clarence
Strait and the ocean entrances of southern Chatham Strait. Small
craft advisories elsewhere. Over land, strong wind gusts to 40 mph
or higher on the outer coast from Cape Fairweather south for late
tonight through the morning tomorrow. Strong wind gusts for
Juneau and the southern inner channels through the day tomorrow.
Strong winds this evening over Skagway are left over from the
previous front and these winds are expected to relax later this
evening.

Very little change in temperatures between now and tomorrow
afternoon with little to no diurnal variability. Pressure updates
limited to Thursday day - used the 12Z NAM12 here. Updated winds
over the gulf for Thursday with NAM as well. Minor tweaks to wind
speeds and directions on the inside. Likewise for overnight lows
and daytime highs. PoP unchanged. used 12Z NAMDNG5 for QPF.
Overall forecast confidence is average.

.LONG TERM...First half of the long range remains very active with
at least two strong systems moving through the eastern gulf in a
36 hour period. The first of these systems, arriving on Thu
night, will be the strongest of the two. Central pressure will
drop to around 975 mb curtsy of the left exit region of a 500 mb
jet streak right over the system for most of its run through the
gulf toward Icy Bay. The associated front that will be moving
through the panhandle late Thu night and early Fri will have some
significant wind. 850 mb winds over the southern half of the
panhandle are forecast to be around 75 to 80 kt at that time. That
should be enough for wind gusts to 60 mph or higher for the
southern half of the area. Kept the high wind watch up for zones
27 and 28 but also added zones 23 (mainly for southern Baranof)
and zones 26 (Kuiu Island and around Sumner Strait) into the mix
as well. The rest of the inner channels will likely see gusts to
40 or 50 mph as the front moves north into Fri morning. These
areas will likely need strong wind headlines.

As for precip, strong warm air advection along with starting temps
already above freezing will cause most areas to stay rain for all
but possibly White Pass and the higher elevations of the Haines
Highway. Expect a few inches of accumulation possible where the
temperatures stay cold enough.

System number two is still expected right on the first one's
heels. Model agreement is still poor with track scenarios ranging
from a track up to Cape Decision (Nam), a track through the
Central gulf toward Cape Suckling (ECMWF), or a much slower
northward speed through the gulf (GFS). At the moment decided to
retain the previous forecast that followed the ECMWF, pending
better agreement from future runs. Mainly looking at another wind
event for the outer coast and southern panhandle with more gusts
to 40 or 50 mph late Fri night. Also looking at another rain
event with more warm air flowing into the panhandle.

Second half of the long range looking much quieter as a ridge
builds over the gulf early next week. Lingering showers late
weekend possible with onshore flow continuing. This will
eventually dry out toward Tues as overall flow turns more
offshore. Few changes for the Extended range at this time.

&&

.AVIATION...MVMC will prevail with pockets of IMC at times due to
low CIGS. Visibility restrictions possible in heavier
precipitation. LLWS and turbulence will become an issue overnight
and last through the day Thursday as a low level southeasterly jet
of 65 kts associated with the front moves over the panhandle from
southwest to northeast. Freezing level around 3000 feet. Watch out
for in-cloud icing above that level.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch from late Thursday night through Friday morning
     for AKZ023-026>028.
     Strong Wind from late tonight through Thursday morning for
     AKZ022-023-027.
     Strong Wind from Thursday morning through Thursday afternoon for
     AKZ025.
     Strong Wind from late tonight through Thursday afternoon for
     AKZ028.
     Strong Wind until 9 PM AKST this evening for AKZ018.
MARINE...Storm Warning for PKZ052.
     Gale Warning for PKZ022-033-036-041>043-051.
     Small Craft Advisory for PKZ012-013-021-031-032-034-035-053.
&&

Fritsch/EAL

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