Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 230051
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
351 PM AKST Sun Jan 22 2017
.SHORT TERM...Complex weather pattern for the next 24 hours. A
weak short wave is currently advancing northward through the
northern panhandle at the moment. This feature has produced little
in the way of precipitation as it has moved north today. Only
very light rain or snow has been observed with most of those obs
along the outer coast or southern panhandle. Some overrunning
precip associated with it is starting to show up over the northern
panhandle with cooling cloud tops on satellite and some flurries
being observed. That feature will continue to trek northward
through the evening.
The feature of more concern is the weak low west of Baranof Island
today and how it interacts with the upper trough currently over
the central gulf. The surface low will be making for Yakutat where
it will head inland late tonight. A weak front will develop to the
east of the low track tonight and move east. Meanwhile the upper
trough will be tracking over the panhandle late tonight and
early tomorrow. Main concerns as the front moves through is ptype
and if it is snow, what the amounts will be. There still is a
decent cold air mass in the central and northern inner channels
right now as well so the contribution from overrunning of that
cold air will need to be considered as well. Current thinking has
most of the northern panhandle staying snow into tomorrow morning
as the southerly push is not that strong. Available moisture for
this system is not substantial either but the overrunning
situation should be enough to squeeze every last drop out of the
atmosphere. So I am going with snow amounts ranging from 3 to 6
inches across the northern inner channels and northern gulf coast
tonight and tomorrow with highest amounts expected at Haines,
Gustavus, Yakutat and Juneau. I have either continued or issued
winter weather advisories for those areas. Amounts may vary in some
locations due to terrain effects and differing strength of the
warm air advection at the surface.
Secondary to the precip is the wind which will not be that
notable with this system. Highest winds expected are in the NE
gulf and near Cross Sound with E winds up to 30 kt at the highest
near the low. Other wind considerations are the remaining winds
in Skagway that are still gusting as high as 40 mph as of 2 pm
this afternoon. Those winds should diminish through the evening.
Main tweaks to the forecast were for low track through the gulf
this evening. Previous forecast had it heading toward Cape
Suckling. Current and most previous model runs were favoring a
track toward Yakutat Bay so changed the forecast accordingly
mainly using Nam for guidance. Mostly local effect changes for
any other updates.
.LONG TERM...Active weather pattern for the extended range
forecast period with at least 4 fronts to affect the panhandle
through next Tuesday. Further, each one of these fronts is
looking like it will contain a significantly higher than normal
amount of precipitable water.
First up is a hurricane force low currently over the western
Aleutians. The low itself is forecast to weaken significantly by
the time it enters the western gulf and not expected to move into
the eastern gulf at all. The front, however, will push all the
way across the gulf and reach the outer coast by Tuesday morning.
Precipitation from this front will still be in the area when the
next front arrives from the west on Thursday. A third will arrive
from the southwest on Friday and appears to have the greatest PW
of the three. High PoPs remain in the forecast for the second half
of the weekend but we may see some dry weather on Monday - a
brief break before the fourth front, the weakest of the 4, arrives
from the south.
The first three fronts will each advect in warmer low level air
and this will trend the snow level up over the course of the
coming week, but not before accumulating snow fall over the
panhandle north of the icy strait corridor and in Juneau through
Tuesday night. Snow may also accumulate in the Hoonah area. By
Wednesday, accumulating snow will be primarily confined to higher
elevations and along the highways. The warm air advection runs out
in the second half of the weekend and snow levels once again fall.
PoP from the 4th front not as impressive, does not push as far
enough north, and is quite far out into the future. Thus
confidence in snow amounts and areal coverage is low. Confidence
is higher that this 4th front will generate snow at lower
The Tuesday and Thursday front will each feature gale force winds
over the eastern gulf with small craft winds over much of the
inner channels. Marginal gales likely on Thursday for southern
Chatham Strait and Clarence Strait. Also, strong winds in the
Yakutat area are likely Tuesday night.
Used NAM, GFS, Canadian NH, and EC for updates to pressure and
wind at various times through Thursday night. No changes from
Friday onward, as the new WPC was not significantly different from
the existing forecast. PoP and QPF for the same timeframe
primarily from Canadian NH with some help from NAMDNG5 and ECMWF.
No changes to temps. Snow level and P-type work done on the
previous shift for Tuesday morning through Wednesday night
preserved without change. Overall forecast confidence is average.
PUBLIC...Winter Weather Advisory from midnight tonight to noon AKST
Monday for AKZ025.
Winter Weather Advisory from 9 PM this evening to 9 AM AKST
Monday for AKZ019.
Winter Weather Advisory until 9 AM AKST Monday for AKZ017-020.
Strong Wind until 3 PM AKST this afternoon for AKZ018.
MARINE...Small Craft Advisory for PKZ022-041>043-051-052.
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