Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
458 PM akdt Sat Aug 1 2015
Analysis and upper levels...
the upper level ridge is over southwest Alaska and building into
southcentral Alaska today. It is still far enough to the northwest
that there is enough instability for showers over the mountains
from the Talkeetna Mountains southward with some thunderstorms
around the Kenai Mountains. What is interesting about this is that
the atmosphere is becoming more stable from the northwest as the
day GOES on which should limit the amount of shower development
from Anchorage northward. Over the Kenai Peninsula the atmosphere
will remain unstable long enough to produce some isolated
thunderstorms in the the early evening. Kodiak Island also remains
an interesting case as the atmosphere is unstable aloft but low
levels have a stabilizing marine layer and sea breezes. Cumulus
clouds began to develop over higher terrain around noon and may
develop into showers and even possibly thunderstorms inland. The
biggest question for their development has been the initial
development and with the cumulus beginning around noon it increases
the possibility for the convection to develop with the maximum
heating of the day.
models continue to do well with the synoptic pattern through the
first half of next week. The feature they continue to struggle
with is the low developing south of the Alaska Peninsula starting
tonight and moving eastward slowly over the next few days. The
good news is that the spread in model solutions is less than
yesterday but the GFS and NAM are still farther east than the
European model (ecmwf) and Gem solutions. The most stable solution from run to run
still appears to be the European model (ecmwf) model.
some warmer and drier conditions are expected in southcentral
Alaska for the first half of next week due to the upper level high
building over the area. Winds will likely remain fairly light and
relative humidity values will not get near critical values. Aside
from the possibility of human carelessness the biggest fire threat
from this pattern will be the possibility of flare ups from the
Duff layer which may still be smoldering where recent fires have
Southwest Alaska will also see some warmer and drier conditions
but there will be more moisture available in southwest Alaska to
keep relative humidity values fairly high for a sunny pattern.
Short term forecast southcentral Alaska (days 1 and 2)...
precipitation over most of southcentral Alaska will be coming to
an end later tonight as high pressure pushes into the area from
the north through Monday. Showers and thunderstorms this evening
are mainly focused along mountain areas where there is still
sufficient moisture to support convection. This...combined with
daytime heating and some orographic lift...will support convective
development mainly over the higher terrain of the Copper River
basin...the Kenai Peninsula...and Kodiak Island. Precipitation
chances on Sunday will be limited to the Alaska Range as a weak
upper level shortwave moves around the periphery of the ridge.
Afternoon temperatures through Monday will rise into the middle to
upper 70s inland and into the upper 60s along the coast as mostly
clear skies will dominate the area. Some inland locations of the
Susitna Valley and the Copper River basin may warm into the lower
Short term forecast southwest Alaska...
stable conditions caused by the high pressure over the Bering Sea
will limit shower development across southwest Alaska through
Tuesday. But the stable atmosphere will also make way for the
development of fog. The mostly likely area for fog is over the
Kuskokwim Delta due to the consistent northwest flow that will
help to advect in fog from the Bering Sea. The next several
nights will likely see fog push inland over the Kuskokwim Delta
that will dissipate each day with the peak heating of the day.
Short term forecast Bering Sea/Aleutians...
fog and stratus will be the dominant conditions for the Bering
Sea and Aleutians as a strong area of high pressure sits over the
Bering. This high pressure will last into Tuesday where it will
finally begin to weaken and push west. A North Pacific low will
also make its way towards the Alaska Peninsula Sunday night which
will start to bring rain to the Alaska Peninsula and the eastern
Aleutians. However...this low will stay south of the peninsula and
weaken early next week.
Long term forecast (days 3 through 7)...
generally sunny skies and seasonably warm temperatures will
remain over the region through the middle of next week as high
pressure continues to dominate the Bering Sea and extends eastward
over the Mainland. Model guidance has come into better agreement
with respect to the cutoff low which will form south of the Alaska
Peninsula and remain in that general vicinity through Wednesday
before passing south of the Gulf later in the week. This will
keep any associated precipitation mainly confined to the akpen
and Kodiak Island. The chance for precipitation will then begin
to increase over the southern Mainland later in the week as high
pressure weakens and an upper trough drops down from the Arctic.
Synopsis and model discussion...ez
southwest Alaska/Bering Sea/Aleutians...dk