Scientific Forecaster Discussion
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Southcentral and southwest Alaska forecast discussion...corrected
National Weather Service Anchorage Alaska
106 PM akdt Tuesday Apr 15 2014
Analysis and upper levels...a very large multi-centered closed
low is anchored over the central Bering Sea and Aleutians. A
separate out of phase low/trough over the Gulf of Alaska is
lifting northward toward southcentral. An east-west oriented ridge
extending from the Yukon to northern Bering Sea is being pushed
northward by both of these troughs...leading to increasing cloud
cover over the southern Mainland.
Model discussion...models are generally grouped in the same
region with synoptic scale features in the first 48 hours of the
forecast...but there are a lot of smaller scale features and run-
to-run continuity is not good. Thus...forecast confidence is below
Models continue to show a double barrel surface low developing in
the central Gulf late Wednesday morning...with the stronger center
of circulation intensifying over the eastern Gulf. There is a
large spread in solutions with the eastern Gulf low...although
most of them have trended toward a deeper slower low. Out
west...the models continue to show a complex surface low over the
central Bering weakening and slowly tracking eastward. Both the
GFS and European model (ecmwf) are showing a slightly deeper solution with this
system...and seem to agree on tracking the low center along the
Aleutian chain in the southern Bering through Thursday morning.
Model spread grows beyond 48 hours with the complex nature of
numerous waves rotating around a closed low center. With low
forecast confidence forecast changes will be kept to a minimum.
Short term forecast...
Southcentral Alaska...the upper level low/short-wave trough over
the Gulf will lift northward across southcentral late this
afternoon and evening. The bulk of precipitation will remain along the
coast. A dry low level airmass inland will keep most areas dry...
although higher elevations will see a period of precipitation as the
upper wave passes through. Meanwhile at the surface a weak low
over the central Gulf will track to the northwest Gulf helping to
strengthen a ridge along the north Gulf coastal zone and
temporarily kick winds up through Turnagain Arm into portions of
Anchorage as well as through the Knik River Valley into Palmer.
Extensive cloud cover will keep temperatures on the cool side
inland which will limit the amount of wind bending into
The next couple upper waves moving up from the east Pacific will
affect mainly the Gulf as the Bering trough swings eastward and
changes the upper flow causing the northward progression of waves
to slow. This Bering trough will ultimately lift northward across
southcentral Friday/Friday night in similar fashion to today's
Southwest Alaska...the remnants of an occluded front is
approaching the southwest coast with areas of light precipitation along
the immediate coast. Don't expect the precipitation to make it very far
inland...but cloud cover will increase as the troughs lift
northward. Southwest Alaska will remain on the periphery of the
many upper waves in the area the next few days...so precipitation will
generally be spotty and light.
Bering Sea/Aleutians...the upper level low will wobble around at
the whim of the various centers...but will gradually shift south
and east over the next few day. Cooler and drier conditions will
move in the wake of the upper low.
Long term forecast...the upper low will become re-centered over
the Gulf this weekend...with all models keying in on an intense
surface low. Expect wet and windy conditions along the Gulf Coast
and Kodiak Island. The west will start the weekend off quiet...but
a trough moving out of Asia late this week will amplify over the
north-central Pacific likely affecting the Aleutians later this
weekend. Model spread with track of this trough and associated
surface low is large...so forecast confidence is low.
Seb/tp Apr 14