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FXAK67 PAJK 161348
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
548 AM AKDT Mon Oct 16 2017

.SHORT TERM...A main low north of Middleton Island, has a
secondary low near the Fairweather grounds. These lows will
eventually merge south of Yakutat and fill early Tuesday morning
as weak high pressure briefly ridges over the Panhandle and
eastern gulf.

Widespread rain showers covers much of the area, with a slight
chance of thunderstorms this morning for marine areas 310, 42-51
and along the coast from Icy Bay to Sitka area. Ice pellets would
not be out of the question in heavier showers, with cold air
aloft and the instability in this area. Showers in northern half
of the Panhandle could produce gusts 10 to 15 mph above the
sustained winds today, the strongest convection will be this
morning and taper off by late afternoon.

Another low near Haida Gwaii will slip into Canada today. The
extreme southern Panhandle, south of Ketchikan and including Hyder
has had heavier rain showers overnight, with heavy rain showers
reported at Annette. By this afternoon Hyder will be the only
portion of our forecast area that will still be feeling the
affects of the low as it continues to move east.

Winds are on the diminishing trend this morning and will be mainly
15 mph or less across the Panhandle and inside waters this
morning. The southern half of the outer coastal marine areas and
the Gulf of Alaska will start increasing in winds 25 to 30 kt by
late this afternoon. Prince of Wales and the Gateway City and
surrounding areas will also see winds increase again this
evening.

SCA due to seas start out today. Then as the winds increase SCA
due to winds will occur starting with marine area 41 and
spreading up to area 42 and 43 by late afternoon.

To start the forecast today the models had banded together with
relatively good agreement, but quickly lost their camaraderie. The
GFS and NAM had the best agreement with low placements of both
the northern and southern lows, with minor differences on
secondary low in the northern area. Even with less than stellar
model agreement, the forecast has been trending well. The overall
message is rain showers, with snow showers in the upper
elevations. Snow accumulations for the Klondike Highway near White
Pass will be up to an inch, while the snow level has risen above
Pleasant Camp on the Haines Highway. Tuesday night will get a
watchful eye with overnight temperatures cooling a bit more and
snow levels lowering down to around 1200 feet near Skagway/Haines.

.LONG TERM.../Wednesday through Monday/ Our general forecast will
persist another day, as only small changes can be made with any
degree of confidence. Wednesday a largescale upper low moves into
the eastern gulf and sticks around until early Thursday when
shortwave energy drops south from a more energetic Arctic system.
How the inevitable surface low dances over the gulf waters may
have large effects on the forecast, especially across the northern
Panhandle. Ensembles have favored a broader, perhaps double-
barreled system extending into the northeast gulf. This would mean
a more moist mid-week forecast with very, very low probability of
lowland snow. The operational GFS stubbornly takes the low well to
our south, meaning drier weather and perhaps cooler temperatures.
This scenario, which we deem less likely, may provide enough cool
air to support snow, should precipitation stick around. But we
must emphasize the word "drier" two sentences above. So let us
discount snow in the mid-range. Whatever the case, the southern
Panhandle looks wet and mild. Winds over the gulf and southern
Panhandle look to steadily decrease through Wednesday as the
system looses momentum and begins to weaken and sap its energy.

With the ECMWF supporting a more northerly position of the eastern
gulf low, we kept the chance of rain for the north, made rain
certain for the south, and steadily increased the rain chances
across the Panhandle through Thursday into Friday as agreement
becomes stronger with short-wave energy spawning more low pressure
in the northern gulf, even in the GFS. By Friday, deeper onshore
flow ushers in potentially more organized moisture and a warming
trend into the weekend. Offshore flow ahead of the system has the
potential for a chance of snow with rain near Skagway on Saturday,
but confidence is low.

Confidence falls for sure beyond the weekend into next week. But
models and ensembles hint at more interaction with tropical
systems from the western Pacific. Where jets drive this deep
tropical energy, we have no real clue, but coastal areas from the
Aleutians north to the Bering Strait and into the Pacific
Northwest and all points between, including Southeast Alaska,
will watch with interest.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ041-042.
     Small Craft Advisory due to Seas for PKZ022-043-051>053.

&&

$$

KV/JWA

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