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Northern Alaska forecast discussion 
National Weather Service Fairbanks Alaska
155 PM akst Thursday Dec 18 2014

Discussion...

While a seemingly quiet forecast period the next 72 hours...their
are issues to contend with. Stratus and/or fog in portions of
interior Alaska tonight...and elevated winds primarily over the West
Coast...the Arctic coast...and portions of interior Alaska beginning
Friday.

Deterministic guidance are generally in good agreement aloft with
the large scale pattern the first 60 hours. Though differences
become more apparent elsewhere...specifically the mslp pattern
south of the Aleutian Islands and the Gulf of Alaska 30 to 60 hours
out. The GFS has drawn closer to the European model (ecmwf) forecasts in the 500 hpa
pattern...compared to previous runs seen yesterday...with respect
to the Sat and sun time frame. Differences appear more comprised
of strength/amplitude generally on sun and Monday than location/phase
aloft.

Otherwise...will be modifying the forecast some in the tonight
period as guidance has been a bit behind in some areas in regard
to handling fog/stratus over portions of the interior. NASA sport
nighttime microphysics depicts fog/stratus over much of the
interior with the latest pass about 19z...in particular its
depiction over the Yukon Flats and on both sides of the Brooks
range. Surface observation show a few sites with visible sub 2 miles at 20z...with
pafa at 1/4sm the lowest. Current thinking is that fog/stratus
will take a longer time to move out...especially over the Yukon
Flats than previously anticipated.

Aloft...

Not much change with respect to the pattern aloft. Broad low
pressure in the Bering Sea east of Kamchatka peninsula...and a low
south of the Gulf of Alaska. Ridge over Southeast Alaska moves
northward to over the northwest territories-northern Alaska Friday. The
low in the Gulf of Alaska will continue to weaken overnight and be
drawn into the broader area of low pressure Friday. Pattern becomes
more progressive as the low in the Bering moves east before
settling south of the eastern Aleutian Islands by late Sat...while
the ridge in northern Alaska moves eastward. Longwave ridge over
Kamchatka peninsula begins building late Sat/early sun...then is
expected to move across the Aleutian Islands sun and Monday as the
low weakens south of the Alaska Peninsula.

Surface...

985 hpa low just east off the coast of eastern Siberia continues to
weaken and will dissipate overnight. A cyclone now southeast of
Shemya at about 966 mb will move east while a low south of the
Gulf of Alaska...that\s currently about 969 mb...stays relative
stationary. Multiple lows are forecast south of the Aleutians Friday
with guidance all showing multiples lows with relatively
similarly positions/general movement. A surface low in the southern
Gulf of Alaska is expected to take hold by late Sat
however...guidance varies in strength and location.

Pressure gradient increasing overnight...that should result in
increasing wind speeds that should help erode some of the status
and fog in the interior. This may not be strong enough for some
areas...especially the Yukon Flats. Winds are expected to become
more moderate and elevated Friday...primarily over higher
terrain...in passes of the Alaska Range...over the Bering Sea...and
portions of the West Coast. The Tanana Valley jet/local wind is
anticipated to start as well later tonight however...winds below
30 miles per hour are expected tonight and Friday. Arctic coast is anticipated
to see strong winds beginning late tomorrow as the pressure
gradient tightens there also.

Overall...dry pattern the next three days with most of the
precipitation activity south of the Alaska Range. Possible patchy
freezing drizzle and flurries will occur in areas where the
stratus holds...especially over the Yukon Flats.
Elsewhere...scattered snow showers over the Arctic coast and
over the Bering Strait coast/St. Lawrence Island are expected as
well.

Coastal hazard potential days 3 and 4...none

&&

Afg watches/warnings/advisories...
heavy freezing spray warning for pkz210.

Small Craft Advisory for pkz210-pkz210.
&&

$$

Et Dec 14

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