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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
154 PM akdt Monday Oct 20 2014

Analysis and upper levels...

Trough axis from Bristol Bay upper low rotating north northwest
across south Mainland this afternoon will pull westward Monday
night and move to the southwest coast by middle day Tuesday. Another
trough axis slipping south across the Bering will swing across the
Alaska Peninsula and Fox Islands then slide into the Pacific by
10 PM Monday evening. As this occurs most of the upper low center
now over eastern Bristol Bay will also move southeast tonight and
eastward Monday passing Kodiak Island by to the south. This will
result in weak easterly flow aloft Tuesday afternoon and night
followed by weak ridging Wednesday. Upper ridge far western Aleutians
will remain progressive with the Main Ridge axis arriving along
the West Coast by Wednesday evening. This ridge will collapse
southeastward Thursday as a strong west southwest jet drives into
the Bering as upper low pressure and Arctic air expands over the
russian far east.

&&

Model discussion...

The models look good out west and are in basic agreement with the
main features and orientation of the pattern heading into late
this week. There are some differences in the exact track and
strength of the 970 mb storm now near 51n 147w moving north into
the Gulf Tuesday and Wednesday. Current track appears to be
farther west than previous runs. Wednesday afternoon the three models
show the average low center longitude position roughly around 145w
to 148w with the NAM showing a 978 mb center at 56n...the ec a 978
mb center at 54n and the GFS a 977 mb center at 52n. The waves
forming forming along the frontal boundary show even more
disagreement.

&&

Short term forecast...

Southcentral Alaska...
precipitation becoming more showery and intermintant as the trough
moves inland. A couple of more bands will move north to the Prince
William Sound and the Kenai Peninsula this evening and tonight and
dissipate over southcentral Alaska Tuesday. Areas of snow along and
west of the Alaska Range will move west to the Bering Sea by Tuesday
evening.





&&

Long term forecast...
a front associated with a low skirting the siberian coast that will
first bring rain and gusty winds to western Aleutians on
Wednesday will then move onshore over the southwest Mainland by
Thursday evening. The remnants of this system will be the
dominant feature in the long term forecast looking into early next
week.

The models are in decent agreement with the upper trough as it
moves over the Bering Strait on Saturday...but then quickly
diverge on Sunday and Monday. The European model (ecmwf) in particular as been the
most sporadic with this feature...digging deep troughs as far
south as the southern Gulf and bringing very active weather to the
southern Mainland. The GFS and GFS ensemble on the other hand has
been much more consistent in keeping a much weaker upper trough
over the central interior...with more typical cloudy and showery
weather over the southern Mainland. After coordination with wpc
this morning...the long term forecast after Saturday heavily uses
ensembles (ec and naefs)...which currently more closely resemble
the operational GFS. Future runs (in particular of the ec) need to
be closely watched however...as a deeper Gulf low would result in
a significantly different long term forecast into next week

&&

Afc watches/warnings/advisories...
public...
marine...gale 155 165 170 172 173 174 179 185. Fire
weather...none.

&&

$$
Oct 14

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