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Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
400 PM akdt Thu Jun 22 2017

Analysis and upper levels...
there is an upper level high draped northeast-to-southwest over
southern Alaska, centered along the Alaska-Canadian border between
Eagle and Northway. The ridge is quite "dirty" with plenty of
clouds and isolated to scattered showers, mainly over the higher
terrain. There is an upper low over the Panhandle that is
weakening and moving east. There is an upper low with an
associated surface low over the southwest Gulf, that is moving
slowly towards the northeast. A fairly strong low is situated over
the western Aleutians, with a leading front over the central
Aleutians. There is an upper level trough just off the coast of
the Kuskokwim Delta area, which is weakening and moving slowly
eastward.

&&

Model discussion...
the numerical models are in good agreement for the short term
portion of the forecast (sunday afternoon). Surface pressure
fields are in very good agreement, therefore forecast confidence
for the marine areas is above normal. For the Mainland, the
models struggle a bit with subtle moisture fields and convection,
which are a big part of the forecast. Therefore the forecast
confidence for the land areas is near to a little below normal.

&&

Aviation...
panc...VFR conditions and light winds will generally persist.
The atmosphere is moist enough that there is some risk of MVFR
conditions, especially in the morning.

&&

Short term forecast southcentral Alaska (days 1 and 2)...

A slow warming and drying trend is underway across southcentral.
Friday looks to be much the same as today, with mostly cloudy
skies, though with more sun breaks, especially later in the day.
An occasional shower or two can't be ruled out especially in the
mountains. The further north and east you go, the more sunshine
and the better the chance of some isolated thunderstorms,
particularly across the Copper River basin and the Talkeetna
Mountains Friday afternoon.

Building ridging from the west into the area Saturday will move
much of the cloud cover eastward with time, so Anchorage and
points west should break out to partly cloudy skies by Saturday
evening. Isolated thunderstorms will be possible again Saturday
afternoon from the Talkeetna Mountains east through much of the
Copper River basin.

&&

Short term forecast southwest Alaska (days 1 through 3)...

Upper ridging over the Alaska Range is interacting with an upper
trough moving east over the y-k Delta coast. This is forming a
favorable region of stretching deformation aloft. An instability
axis has formed this afternoon from the Kilbuck Mountains to the
higher mountains of the Alaska Range. Isolated thunderstorms will
continue into the evening before becoming more organized as a
band of showers along the deformation zone Friday. This will
favor the lower Kuskokwim valley and the interior mountains with
rather widespread rain showers. Meanwhile, weak flow around the
Alaska Peninsula, the coast of Bristol Bay and the Kuskokwim Delta
will keep low stratus and fog in place tonight and Friday
morning.

Friday, the upper trough will weaken, but the instability axis
will keep thunderstorm threats across the interior while more
stable marine air keeps the coasts dry but prone to sea stratus.

Saturday shortwave ridging will begin to build with showers
shifting east toward the Alaska Range before falling apart
Saturday night. Sunday will continue to warm as the ridge aloft
builds.

&&

Short term forecast Bering Sea/Aleutians (days 1 through 3)...

A closed upper low and associated weak gale force occluded front
over the western and central Aleutians will slowly shift east
before another upper trough merges with it. This will spread
frontal precipitation to the remainder of the Bering Sea Saturday
and Saturday night. The main surface low will stall over the
western Bering Sea Sunday.

&&

Long term forecast (days 3 through 7)...

The upper level low moving into the southern Gulf will not make it
as far north as previously forecast thus the weak ridge across the
interior will hold. As the upper low moves off to the east, the
upper ridge builds back over western Alaska Sunday and Monday. As
this ridges builds it will slide east as a strong upper low pushes
into the central Bering Sea late Sunday. Monday through Wednesday
we expect the upper low to retrograde back into the northwest
Bering Sea with a trough extending southeast across the Alaska
Peninsula into the southwest Gulf of Alaska.

What this means for the sensible weather is we expect a warm dry
weekend for the southwest Mainland while the Aleutians and Bering
Sea will transition from the fog and stratus regime to the more
active cloudy rainy weather beginning Friday night. Cool cloudy
conditions should extend into the southwest Mainland for the
beginning of next week to mid week while the central Bering Sea
and Aleutians remain in the cloudy, wet and windy weather.

Model agreement has remained consistent through the long term and
the National guidance remained heavily weighted toward the
operational GFS model guidance through the weekend. The ec is a
bit of an outlier as we head to Tuesday and wpc stayed the course,
heavily favoring the GFS for their solution.

&&



Afc watches/warnings/advisories...
public...none.
Marine...gales 175 176 177.
Fire weather...none.

&&

$$

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