Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
146 PM akdt Thursday Aug 21 2014
Analysis and upper levels...upper low western Aleutians. Main jet
south of the area as it rides over the northeast Pacific Ridge.
Otherwise a light southwesterly deliquescence flow is seen across
all of the southern Mainland.
Model discussion...at this point preferring the GFS over the NAM
since it has a good handle on the system at 39n 171e, but may go
with a compromise Sunday afternoon and evening. The weak
disturbance now passing south of Kodiak into the Gulf stays south
with nearly all of the precipitation remaining offshore. A very
weak upper low does slip into southern Prince William Sound by
midday Friday. Models take the western Aleutian upper low and
move it to Bristol Bay late Sunday and then track it eastward
across southern Alaska Monday. NAM is slowest doing this. There
are the usual differences with the triple point low and waves
forming along the front. GFS and ec spread rain with the occluded front
well into southern Alaska while the NAM keeps it mostly south of
the north Gulf Coast.
Short term forecast...
Cook Inlet fog will be less extensive
tonight and Friday morning due to an increase of midlevel
moisture and increasing outflow through Turnagain Arm. Weak
diffluent upper flow supports scattered mountain showers and
isolated thunderstorms Thursday evening. Weak upper ridging ahead
of the Aleutian storm will suppress this Friday evening with only
isolated showers possible.
Southwest Alaska...variable clouds with scattered or isolated
showers this afternoon and evening should be more isolated Friday
and Saturday as higher pressure builds in. Rain should reach the
coast Saturday night and spread inland toward morning which will
make for a cloudy wet day on Sunday. No significant winds
expected but may increase to 20 to 30 kts Saturday night ahead of
Bering Sea/Aleutians...cloudy with periods of rain or showers
through the weekend. Dry in the west as higher pressure moves in
followed by rain Saturday night and Sunday as the next front moves
in. No gales expected.
Long term forecast...
an upper level low will continue to track across the Alaska
Peninsula into the southeast Mainland by the early part of next
week. This will bring showery conditions with small craft winds
into the Gulf of Alaska. The Bering Sea will have an upper level
long wave trough near the Kamchatka peninsula dropping down into
the western Bering Sea and western Aleutians by Monday. This
feature will have a surface low at the base of the trough near the
western Aleutians and will slowly move eastward across the
Aleutians from Wednesday into next weekend. This will produce
showery conditions with marine layer stratus and fog.
Db Percy Aug 14