Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
403 PM akdt sun Aug 2 2015
Analysis and upper levels...
the upper level high over the Bering Sea is making its way over
the interior of the state this afternoon and bending into
southcentral Alaska. An upper level low just south of the Alaska
Peninsula is keeping the upper level ridge from pushing into the
area with more authority. A series of weak short waves have
rotated around the periphery of this ridge which brought in some
clouds over southcentral Alaska this morning with a few more high
clouds possibly overnight with another weak wave that can be seen
best in the infrared satellite.
The atmosphere remains just slightly unstable over southcentral
Alaska and the Copper River basin this afternoon with just enough
lift for a few showers over some of the mountains. Southwest
Alaska is under a more stable atmosphere under the upper level
high which has allowed a lot of marine stratus to makes its way
inland...though the sun is burning much of this off during the
models continue to do well with the synoptic pattern through most
of the week. The discrepancy in position and movement of the low
south of the Alaska Peninsula and moving toward the southern Gulf
has largely been resolved.
Both the NAM and GFS are showing the atmospheric instability in a
similar manner for Monday and Tuesday with very little over the
area Monday but some returning to the Susitna Valley especially on
Tuesday. The NAM is much stronger than the GFS which is typical
but the similar geographic coverage pattern on both increases
confidence in some diurnal showers developing again by Tuesday
and into Wednesday.
the shortwaves over southcentral have assisted in keeping the
humidity fairly high in spite of warm temperatures. This will
remain the situation with a good stretch of warm temperatures
through the first half of the week over southcentral. The dewpoints
will remain fairly high over the region keeping relative humidities
from dropping very low. In addition the overnight recovery will
remain excellent with the longer nights in August as compared
with the warm stretches that occurred in June.
In southwest Alaska plenty of moist marine air will keep relative
humidity values on the high side so no real fire weather concerns
west of the Alaska Range.
Short term forecast southcentral Alaska (days 1 and 2)...
warm and dry conditions will settle in over southcentral Alaska
through Tuesday as skies clear beneath the ridge extending over
the Mainland. The low south of the Alaska Peninsula will bring a
chance of rain to Kodiak Island beginning late Monday night as it
tracks towards the southern Gulf. The potential for diurnal
convection will slowly return starting Tuesday afternoon as high
pressure begins to weaken overhead and instability increases...
however any thunderstorm activity should remain isolated in nature
and confined mainly to the Talkeetna Mountains.
Short term forecast southwest Alaska (days 1 and 2)...
building high pressure aloft and offshore flow will work in tandem
to gradually warm the region through Tuesday. The stable air mass
will also keep the region dry...with the exception of portions of
the Alaska Peninsula on Monday night and Tuesday where rain chances
will increase in association with a slow moving Pacific low tracking
toward Kodiak Island. Enough instability will build late Tuesday
afternoon and evening for a slight chance of isolated thunderstorms
along and near the Alaska Range...but the remainder of the region
will remain stable and dry. Patchy fog will once again be a threat
along the Alaska Peninsula tonight...but increasing offshore flow
tomorrow should largely end fog chances thereafter.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
high pressure over the Bering Sea will keep marine stratus and
areas of patchy fog over the entire Bering and Aleutian chain
through the period. An isolated shower threat is possible this
evening and tonight for the Pribilof Islands as a weak system
moves overhead...but this will quickly weaken by tomorrow. A slow
moving North Pacific low will bring steady rain to the eastern
Aleutians tonight through Tuesday...as well as gale force easterly
Long term forecast (days 3 through 7)...
Tuesday night a stacked low pressure system will be tracking east
from near Sand Point to the southern Gulf through the end of the
week. Gusty small craft winds and rain are expected around the
core of the low as it maintains strength on its path to the
eastern Gulf. Also...gusty winds increase across the Copper River
valley and through channeled terrain of Turnagain Arm on Wednesday
into Thursday as the Gulf low tightens the surface gradient along
the coast. Otherwise...dry conditions are expected across the
southern Mainland and the Bering Sea while under the influence of
For the second half of the work week...two upper level lows move
active weather toward the forecast area with a progressive weather
pattern persisting into the weekend. The first system that drives
weather to the southern Mainland...digs from the northwest on
Wednesday night. The southward extent of this system remains
unresolved...but it brings the next potential for rain along the
Alaska Range and southcentral on Thursday. The other system moves
up from the North Pacific to the western Aleutians Wednesday night
into Thursday morning. This storm system is expected to bring a
front with possible gale force winds and rain. The front pushes
into the central Bering and eastern Aleutians by Friday. This
system is projected to pick up its pace into Saturday with the
front spreading rain into the southwest. Models are not in good
agreement on both of these next systems...therefore a conservative
blend of the ec and GFS was utilized to update the long range
Marine...Gale Warning 155 172.
Synopsis and model discussion...ez
southwest Alaska/Bering Sea/Aleutians...ja