Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 060044
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
344 PM AKST Mon Dec 5 2016

.ANALYSIS AND UPPER LEVELS...
The upper level pattern is shifting some as the ridge has moved
over northern Alaska and a trough has begun to move into southern
Alaska from Canada. This digging trough will help keep the
surface low, which is currently approaching Kodiak Island from the
southwest, in the Gulf of Alaska as it moves eastward keeping
surface high pressure over mainland Alaska.
A weak warm front that is associated with this low is moving over
Southwest Alaska and Cook Inlet today and will stall as it runs
into the high pressure over the state.

&&

.MODEL DISCUSSION...
Models remain in good agreement through the mid term with no
significant differences to discuss. Any small differences should
cause little to no impact to the forecasts.

&&

.AVIATION...
PANC...The only real question for the TAF will be how low the
clouds will be as they move up Cook Inlet with the weak warm
front. Ceilings should remain over the traditional MVFR level of
3000 ft but could see periods overnight where they drop to 5000
ft or below.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

The surface low crossing the Alaska Peninsula will track through
Sitkinak Strait along the south end of Kodiak Island tonight.
This low will spend much of Tuesday just to the southeast of
Kodiak Island before continuing into the southern Gulf Tuesday
night and Wednesday. The associated frontal system will bring a
couple of inches of additional snow to Kodiak Island tonight. Snow
will spread further north along the eastern Kenai Peninsula and
northern Gulf coast tonight and Tuesday, but will taper off
quickly further inland as it runs into the very cold and dry air
mass entrenched over interior Alaska, the Copper River Basin and
Susitna Valley.

While the pressure gradient has slackened significantly across the
Alaska Range, the cold air pool deepening in the Copper River
Basin has kept the northerly offshore gradient stronger along the
northern Gulf coast. The resulting north to northeast winds
through Thompson Pass and across the Copper River Delta will
continue tonight and Tuesday and then strengthen Tuesday night and
Wednesday. Several weak waves rotating around the broader upper
low centered over the Gulf will rotate through the northern Gulf
through midweek bringing additional periods of snow to the Gulf
Coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A triple-point low in southern Bristol Bay currently will
continue to move east toward Kodiak Island and the western Gulf of
Alaska through tomorrow. Overrunning light snow and clouds will
likewise slowly shift south and east through tonight. High
pressure builds in from both the Bering and northern Alaska
through early Wednesday, with a weak inverted trough remaining
over the Bristol Bay region allowing for some low-level to mid-
level moisture contributing to flurries or light snow to remain
over parts of the Bristol Bay region into mid-week, especially
toward higher elevations and sheltered locations. This pattern
then becomes locked into place as the overall upper-level
stagnates Tuesday into Thursday. This will result in clearing
skies except for some low stratus across some sheltered locations.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Cold advection rain and snow showers changing to snow showers will
gradually diminish over the eastern half of the Bering as the
triple-point low moves into the western Gulf of Alaska through
mid-week. Elsewhere, the central Bering will see relatively benign
conditions for the next several days as a narrow, high amplitude
ridge builds overhead. The next front will then move over the
western tip of the Aleutians by Tuesday morning, bringing another
round of strong southerly winds and potentially heavy precipitation.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The days 3 and 4 forecast begin on Wednesday afternoon and will be
characterized by widespread middle and high clouds inland, with
snow showers along the north gulf coast. The greatest
concentration of snow showers will be in the western Prince
William Sound area. Inland areas will likely only see flurries if
anything.

A weakening upper-level low pressure will be spinning in the Gulf
at the onset of the forecast. Showers in the Gulf will be forced
by waves rotating around the upper low as well as unstable low-
level flow, and orographic upslope on the eastern Kenai Peninsula.
A more substantial disturbance comes across the Gulf on Thursday
in the form of an inverted trough. Details of this disturbance are
not well agreed upon, but it does look like a likely short period
of snow for the north Gulf coast; more uncertainty inland.

The extended forecast (Friday-Tuesday) will be very similar to
current conditions; gusty winds along the North Gulf Coast will
be accompanied by cold, dry arctic air from the interior. The same
developing blocking high will stay anchored over northwest Alaska
keeping a steady offshore flow of reinforcing arctic air over the
mainland.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory Thompson Pass.
MARINE...Gales 127 130 178 411.
         Heavy Freezing Spray Warning 127 140 160 180 181.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...ML


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