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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
559 am akdt Wednesday Oct 1 2014

Analysis and upper levels...

Cool and dry conditions are being observed over much of
southcentral and the southwest high pressure
continues to build in from the West. Gap winds around Prince
William Sound have diminished overnight in response to a weakening
surface pressure gradient as well as diminishing northwest winds

Out west...the pressure gradient has begun to tighten across the
southern Bering and Aleutians as a vertically stacked low in the
North Pacific continues to drift northward and encounter entrenched
high pressure in the northern Bering. As a result...gusty
easterly winds and gap winds are currently being observed over
parts of the akpen and eastern Aleutians. Further west...a slow
moving front associated with a low tracking along the Kamchatka
peninsula is currently bringing gusty winds and rain to the far western


Model discussion...

Models remain good overall agreement on the evolution of the
basic features throughout the short term (84 hour) forecast
period. As the vertically stacked low south of the Aleutians
slowly moves toward the Gulf for the latter half of the week...a
strong shortwave and associated reinforcing shot of cold air will
drop down the front of the large ridge over the Bering Sea. As
these two features collide in the northern Gulf...the models are
struggling with the timing...strength...and placement of a series
of triple-point lows expected to form along the old frontal
boundary. The overnight runs trended toward a stronger low
center in the Gulf by Thursday afternoon...but with the ongoing
uncertainty among the models...the morning forecast will show a
more cautious trend toward a deeper low. The 00z GFS became the outlier
regarding this it was both the weaker and slower
solution with the triple point low tracking through the Gulf
Thursday afternoon through Friday afternoon. Thus...the eastern
domain favored a blend toward the European model (ecmwf) solution. However...the
GFS remained the preferred solution over the western domain with
better run to run consistency regarding the vertically stacked
systems south of the Aleutians and also east of the Kamchatka


Short term forecast...

Southcentral Alaska...
cool and dry conditions with diminishing winds are expected to
continue across much of southcentral Alaska through Thursday
morning. Strong easterly winds and increased cloud cover in
advance of the approaching low will start pushing toward the
southern Gulf during the day Thursday. Gales will continue to
spread north with the triple point on Thursday night and local gap
flows will redevelop across the southern Mainland with increasing
pressure and temperature gradients. Precipitation should begin to
encroach on the northern Gulf Coast Thursday night...and spread
inland as early as Friday morning over the eastern Copper River
basin. The westward extent and character of the precipitation
inland on Friday is still uncertain given the current model differences. seems that the northern Gulf Coast will mainly
experience rain and the Copper River basin could see a mix of both
rain and snow Friday.

Southwest and dry conditions are expected to
continue over the area through early Thursday morning with
ridging over much of the southwest Mainland and low pressure
entering the Gulf. Gusty winds along the Alaska Peninsula and
eastern Aleutians will persist and even strengthen through the low south the Aleutian chain tracks northeast
and tightens the pressure gradient up over the area.

Bering Sea/Aleutians...rain and wind will continue brush the
eastern Aleutian Islands as the low continues to slowly track
eastward. Otherwise high pressure will dominate over much of the
central and eastern Bering Sea....continuing the split-flow
blocking pattern and providing very quiet conditions for most of
the region. A vertically stacked low east of Kamchatka and
associated front will bring wet and windy conditions to the
western most Aleutians through Friday morning.


Long term forecast (sat Oct 4 - Tuesday Oct 7)...

Beginning the extended period Saturday...a highly amplified
pattern will continue across the region...with a blocking ridge
extending from the Bering northward into Siberia...and a longwave
trough over the state of Alaska. Eventually the trough will
develop into a closed vortex aloft over southern Alaska and will
remain in place through Tuesday. While there will not be a
subtropical connection...weak disturbances rotating around the
periphery of the low will support rain and snow chances across
portions of southern Alaska mainly east of the Alaska and Aleutian
ranges. The best chances for rain...then snow...will be across the
Copper Basin. Arctic air will continue to filter into southern
Alaska through the weekend...with gradually cooling temperatures.
Right now...the coldest temperatures will likely develop on Monday
and Tuesday as the upper vortex slowly translates east and colder
air and clearer skies form across the state.


Afc watches/warnings/advisories...
Marine...gale 132 150 155 172 174
fire weather...none.



Tp Sep 14

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