Storm Warning 8, NWS Juneau, AK

831 
FZAK67 PAJK 270025
OFFAJK

Offshore Waters Forecast
National Weather Service Juneau AK
325 PM AKST Mon Feb 26 2018

Offshore waters forecast for Gulf of Alaska east of 144W

Wind forecasts reflect the predominant speed and direction
expected. Sea forecasts represent the average of the highest
one-third of the combined windwave and swell height.

PKZ398-271830-
325 PM AKST Mon Feb 26 2018
.SYNOPSIS FOR THE EASTERN GULF OF ALASKA...
As strong low pressure resides in the Canadian Yukon a new storm
force low will track E along the northern gulf Monday night into 
Tuesday. 

$$

PKZ310-271830-
Gulf of Alaska North of 55 Degrees North and East of 144 Degrees
West-
325 PM AKST Mon Feb 26 2018

...STORM WARNING TONIGHT...

.TONIGHT...W wind 50 kt. Seas 23 ft. Rain and snow showers.
.TUE...W wind 45 kt diminishing to 35 kt in the afternoon.
Seas 23 ft. Snow showers. 
.TUE NIGHT...NW wind 30 kt. Seas 15 ft. Rain and snow
showers. 
.WED...NW gale to 35 kt. Seas 16 ft. 
.WED NIGHT...N gale to 35 kt. Seas 15 ft. 
.THU...N wind 30 kt. Seas 12 ft. 
.FRI...N wind 25 kt. Seas 7 ft. 
.SAT...Wind variable less than 15 kt. Seas 6 ft or less. 

$$

118 
FZAK67 PAJK 271258
OFFAJK

Offshore Waters Forecast
National Weather Service Juneau AK
358 AM AKST Tue Feb 27 2018

Offshore waters forecast for Gulf of Alaska east of 144W

Wind forecasts reflect the predominant speed and direction
expected. Sea forecasts represent the average of the highest
one-third of the combined windwave and swell height.

PKZ398-280700-
358 AM AKST Tue Feb 27 2018
.SYNOPSIS FOR THE EASTERN GULF OF ALASKA...
A storm force low will track E along the northern gulf and weaken
as it moves into the Yukon through Tuesday. A ridge will persist 
over the inner channels. Another low will develop over the central
gulf Tuesday to be over the northeast gulf by Tuesday night. 

$$

PKZ310-280700-
Gulf of Alaska North of 55 Degrees North and East of 144 Degrees
West-
358 AM AKST Tue Feb 27 2018

...GALE WARNING THROUGH TODAY...

.TODAY...W wind 40 kt diminishing to 30 kt in the afternoon. Seas
22 ft. Rain and snow showers.
.TONIGHT...SW wind 25 kt becoming NW 30 kt late. Seas 15 ft. Rain
and snow showers. 
.WED...NW gale to 35 kt. Seas 16 ft. 
.WED NIGHT...N wind 30 kt. Seas 15 ft. 
.THU...NE wind 30 kt. Seas 11 ft. 
.FRI...N wind 25 kt. Seas 6 ft. 
.SAT...Wind variable less than 15 kt. Seas 6 ft or less. 

$$

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
254 PM AKST Sun Feb 25 2018

.SYNOPSIS...Low pressure in the southern Panhandle will exit into
central BC Sun night as a weak front moves into the northern
Panhandle. A storm force low will track across the northern gulf
Mon morning and reach the northern Panhandle Mon afternoon. On
Tue another strong low will enter the northern gulf.

&&

.SHORT TERM.../Through Tuesday/ Main forecast concerns will be
precip amounts/ptype and winds. Expect some weak overrunning
precip to develop ahead of the main occluded frontal band early
Mon morning. This will be mainly over the N where there is some
cold air in the lower levels. Precip will increase rapidly Mon
morning as occluded front moves in. Strong jet support and onshore
flow in mid-levels will enhance precip somewhat. The big question
will be how fast snow transitions to a mix or rain. The boundary
layer looks like it will be fairly mixed which will mean sfc temps
will warm more quickly, so anticipate a lower critical 1000-850
mb thickness will be transition line. Think a 1285m thickness will
be that line. This will mean snow should mix with rain by midday
over much of the N area. One thing that could delay the transition
some is if heavy precip rates are going on during the frontal
passage. System is fairly dynamic and with onshore flow, heavier
precip will be possible along S and W slopes. Snowmelt cooling
could keep it all snow until the front passes by early afternoon.
Am currently thinking a general 3-6 inches of snow will fall over
the N third of the area before any rain mixes in, so am issuing
WWA for zones 17, 18, 19, 20, 22, and 25 for the Mon morning
hours. Left zone 21 out of the WWA as the WSW flow will have a bit
of a downslope component that limits precip amounts some and
helps warm things up a bit faster. The S will be a bit warmer to
start so think snow there will be shorter in duration before a
change over to rain during Mon morning. Could see up to 3 inches
of snow in zones 24, 26, and 29 with locally higher amounts near
PAPG and Hyder. Zones 23, 27 and 28 will probably see an inch or
less of snow for most of those areas. Think the only areas that
remain all snow after 00z Tue will be higher elevations of the
highways up N, and Hyder.

Precip should become showery within a few hours after frontal
passage. During first 12 hrs of the showery regime, think most
precip will be rain showers but some snow could mix in during
heavier showers. Colder air moving in late Mon night and Tue
morning will cause more of the showers to fall as snow by late Tue
morning, especially over the N half of the area.

N winds will rapidly decrease this evening over the N then start
to flip around to southerly late tonight and rapidly increase Mon
morning. Think gales will occur over much of the inner channels
Mon ahead of the approaching front. After FROPA, winds will become
more westerly in many areas, and there could be storm force winds
in Cross sound Mon afternoon. Over the gulf, strong W-SW winds
will occur to S of the low track, with gale to storm force winds
expected during Mon into Mon evening, with a slow decrease for
later Mon night and Tue but still in the 30-35 KT range by Tue
afternoon.

We made sure to apply strong gusts to 45 mph across
many areas including Juneau, Skagway, Sitka, and Elfin Cove.
Other areas will be very breezy and may indeed reach threshold
gusts of 40 mph but we will keep them around 30 to 35 mph for now.
Given temperatures and moisture content of the snow, we elected
to remove the blowing snow in the lowlands, as impacts and
visibility degradation will be negligible.

.LONG TERM.../Tuesday night through Sunday/ As of 11 pm Saturday:
At mid levels 500 mb trough extending from a low over the arctic
digs into the central AK gulf with amplified ridging building over
the western gulf Tuesday. The trough will dig towards Haida Gwaii
as the sharpening ridge axis builds toward the Chukchi Sea
setting up an omega block for the rest of the week. At the surface
the remnants of the Monday system in the NE gulf will push some
remaining shower activity over the panhandle then transition to a
dry period. As the energy from this system drops south under the
digging mid level trough a low will reform over Haida Gwaii,
resulting in increasing pressure gradient between it and high
pressure over the Yukon. Main impact from this developing pattern,
besides dry and clear, will be an increase in outflow and
northerly winds, at least gale force over the inner channels and
out of interior passes with gusts of 40 to 50 mph. Also expect
much colder air to stream in from western Canada with temps
dropping into the teens to possible single digits over night.

Models were in fair agreement initially with the timing of the
building ridge. Used a blend of 00z NAM/GFS which over all still
in line with previous forecast. Used more NBM/WPC for Thursday to
increase outflow winds over the panhandle and lower temps. could
still drop temps a few more degrees. Typical with any blocking
pattern models are showing large spread in determining how/when
the ridge will break down with a transition to more zonal flow.
GFS breaks the ridge down the fastest, so held off on using it in
later grids keeping with WPC. Forecast confidence is average
initially then drops by the weekend.

&&

.MARINE...Strong northerlies through Lynn Canal will finally
diminish late this afternoon and this evening as low pressure in
the south pulls away into central BC. Then a weak front slides
into the northern Panhandle that will wrestle northerly winds back
to southerly. This will set up for the main event when a storm
force low ushers 30 to 50 kt winds from the gulf into the Inner
Channels for Monday. As there will be cold air advection behind
the system, we fully expect the instability to transfer some of
these super-impressive 925 mb jets down to the surface. We do
emphasize that there will be a period of very strong westerlies
throughout Icy Strait even into Auke Bay, especially Monday
afternoon. Likewise, Lynn Canal winds will not stay shy after a
period of relative calm tonight. Seas of 20 to 30 feet will
present more hazards across the Gulf of Alaska. Winds will be
lighter across the southern Inner Channels, but still very breezy.

While still there is much disagreement with the parent low
sneaking in to the northern gulf on Tuesday. However, models are
coalescing on another southwesterly wind episode for the Inner
Channels. Therefore, we raised wind speeds and seas across the
channels at this time. However, we do not view it as such a strong
episode as Monday.
&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory from 6 AM to noon AKST Monday for AKZ018-
     019-025.
     Winter Weather Advisory from 3 AM to noon AKST Monday for AKZ020-
     022.
     Strong Wind Monday afternoon for AKZ023.
     Winter Weather Advisory from midnight tonight to noon AKST
     Monday for AKZ017.
MARINE...Storm Warning for PKZ022-051.
     Gale Warning for PKZ011>013-021-031-032-041>043-052.
     Small Craft Advisory for PKZ033>036-053.

&&

RWT/JWA/PRB

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