Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
426 am akdt Sat Aug 1 2015
Analysis and upper levels...
upper level ridging continues to build from the southwestern
Bering northeast into the southern interior of the Alaska
Mainland...with a narrow yet weak upper level trough situated from
an upper level low center near Yakutat west-southwest through the
southern Gulf to just south of the Alaska Peninsula and eastern
Aleutians. Between the ridge to the north and the trough to the
south...an unstable atmosphere remains from the central Alaska
Peninsula to near Kodiak Island to the coastal mountains of the
southern Mainland north and east to the southern Copper River
basin. To the north of this line...conditions continue to steadily
stabilize as middle-level temperatures warm.
models are in good enough agreement to give a high amount of
confidence in the forecast well into the early part of next week.
The main area of disagreement in the last 24 hours had been
centered on a stacked low pressure system that develops Sunday in
the North Pacific about 350 miles southeast of Dutch
Harbor. The GFS and European (ec) models have come into good
agreement with the placement and evolution of this
feature...developing the low into a low-end near-gale force low
that meanders north toward the Alaska Peninsula Monday and Tuesday before
sliding slowly east the middle part of next week toward the far
southwest Gulf of Alaska. The places this will impact the most
will be the Alaska Peninsula (and possibly the eastern aleutians)
on Monday into Tuesday and then the Gulf of Alaska region toward
Wednesday and Thursday. Inland areas will not be impacted as much
due to the track remaining in the far southern part of the
forecast area regardless of the timing. High pressure with above
normal temperatures and little if any shower activity can be
expected especially for inland areas.
the early part of next week will see some warmer temperatures and
lower relative humidity values in conjunction with the upper level high pressure
over southern Alaska. However these relative humidity values are not expected to
be unusual low with lowest values in the middle to upper 20s in
interior parts of southcentral Alaska. Humidity will be higher
west of the Alaska Range as low level moisture off Bristol Bay
will make it inland.
Short term forecast southcentral Alaska (days 1 and 2)...
The building ridge into the Mainland from the Bering Sea will
continue the trend for warmer and drier conditions as we move
through this weekend into early next week. An upper level
shortwave moving ahead of the ridge axis will provide enough
instability for some convective potential mainly along the Chugach
Mountains in the southern Copper River basin and along the
Talkeetna Mountains. The offshore flow will not be as significant
today allowing for the sea breeze to develop in coastal locations.
This will suppress high temperatures for coastal locations below
yesterday's very warm readings.
Short term forecast southwest Alaska (days 1 and 2)...
high pressure continues to build in over the Bering with the
associated ridge tracking over the southwest. This will continue
to clear out the skies over the area...with the exception of
afternoon with some residual instability and unstable conditions
along the akpen. This along with daytime heating will result in
convection over the Alaska Peninsula this afternoon. Otherwise,
warmer air aloft will become more abundant over much of the
southwest Mainland through the weekend...stabilizing the
atmosphere and clearing out much of the cloud cover. With the high
in place fog development is likely...especially along the coast.
With westerly/onshore flow off the Bering near the Kuskokwim Delta
fog will likely be advected inland.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
with high pressure over the Bering Sea...stratus and fog will
remain abundant through the weekend. Further west...a weak trough
will move in near the western Aleutians and stall out Saturday
bringing in some lighter rain to the islands. Then on Sunday
evening a North Pacific low will approach the Alaska Peninsula
bringing some more steady rain to the area.
Long term forecast (days 3 through 7)...
Generally pleasant conditions marked by abundant sunshine and
warmer temperatures will settle over the region through the middle
of next week as high pressure remains over the Bering Sea and
extends eastward over the Mainland. As mentioned in the model
discussion section...a cutoff low develops over the North Pacific
to the south of the Alaska Peninsula Sunday in response to the
building ridge over the Bering. The areas impacted will be mainly
confined to the akpen/eastern Aleutians before beginning to
approach the western Gulf of Alaska region by Wednesday.
Synopsis and model discussion...cirrocumulus
southcentral Alaska...surface observation
southwest Alaska/Bering Sea/Aleutians...tp