Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
437 am akdt Monday Jul 6 2015
Analysis and upper levels...
the high pressure remains positioned near 51n 141w with a ridge
axis extending into the eastern Gulf. The satellite imagery is
showing mostly sunny skies with this ridge over the eastern Gulf
except for some high clouds spilling over the ridge. Upstream
there is a frontal boundary moving through the southwest Alaska
and the southwestern Gulf this morning. This is bringing a large
swath of moisture to the southwest/southcentral area streaming
from the south to north direction. This coincides with the strong
southerly 100 knot meridional jet streak located over the
southwestern Gulf through the Kodiak Island extending into
Bristol Bay interior and the lower Kuskokwim valley. This can
also be seen on the radar imagery showing numerous showers moving
through the southwest Alaska region with remnants of the front
moving up through the Cook Inlet and the Kenai Peninsula. The
upper levels have a closed low in the western Bering Sea with an
associated trough extending towards the Pribilof Islands through
the Dutch Harbor area into the North Pacific. This is reflected at
the surface with a gale force low over the central Bering Sea with
a frontal boundary extending through the central Aleutians just
west of Nikolski this morning. The satellite imagery is showing
wrap around moisture on the backside of the surface low streaming
into the central Bering into the central Aleutians.
the models remain in good agreement with the North Pacific low as
it tracks farther north into the central Bering Sea this morning.
The models depict the low pressure system tracking to the western
Bering and becoming almost stationary through the next several
days. By Tuesday the GFS is faster with the trough moving through
the central Aleutians but the GFS/NAM are in good agreement with
this feature. The high pressure remains parked near 51n 141w with
the associated ridge extending into the eastern Gulf before
regressing farther south into the Pacific by midweek. The
preferred models of choice were the GFS/European model (ecmwf) through the short
term with the forecast confidence remain above average.
the southwest Alaska region will continue to have onshore flow
with the remnants of the weather front pushing through the
region. This will give way to scattered showery precipitation
before an upper level shortwave moves into the Bristol Bay
interior by late Monday evening and tracks through the
upper/lower Kuskokwim valley. This will bring widespread wetting
rains through Tuesday accompanied by cooler temperatures with
clouds and moisture through the southwest Alaska region.
The southcentral region has the upper level ridge moving farther
eastward and will be over the Yukon territory by Tuesday. This
will continue to bring lower humidities to the Copper River
basin. While...upstream there will be several shortwave troughs
beginning to swing the southcentral region by Monday afternoon.
This will increase the pressure gradients resulting in gusty winds
in the Copper River basin...Turnagain Arm and Portage Valley area.
By late Monday evening the last shortwave will push through the
southcentral region accompanied by widespread wetting rains except
for the downslope areas on the Lee of the Kenai/Chugach Mountains.
As the trough exits the region this will result in weakening of
the pressure gradients and cooler temperatures with a showery
pattern through southcentral as we head into the midweek.
Short term forecast southcentral Alaska (days 1 and 2)...
high pressure sits over the southcentral which will help to raise
temperatures this afternoon...especially in the Copper River
basin and Susitna Valley. However...these clearer skies will be
short lived as a front that is currently over Kodiak will move
over the Kenai Peninsula this afternoon and the rest of the
southcentral tonight. The front has been bringing rain to Kodiak
and it is expected to bring that rain to all areas of the
southcentral by Tuesday morning. Ahead of the front winds will
increase with the strongest winds being through east-west oriented
gaps. The majority of the stronger winds will die down by Tuesday
morning. Rain showers will then linger in the area for much of
Tuesday slowly diminishing into the evening.
Short term forecast southwest Alaska (days 1 and 2)...
widespread rainfall will continue over southwest Alaska through
tonight as the front pushes northwest into interior Alaska.
Stratiform rainfall will switch over to mostly showers later
tonight with the chance of precipitation decreasing first along
the coast this afternoon followed by the inland areas late
tonight. A chance of showers will stay in the forecast through
Tuesday night as several shortwaves move through the region.
Winds will gradually decrease throughout the day today with the
strongest winds expected along the coast and through kamishak gap
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
the low located in the south-central Bering Sea this morning will
continue to be the dominate weather feature through Tuesday night
as the low moves into the southwest Bering Sea and weakens. Winds
to gale force are expected today through the eastern Bering Sea
and Pribilof Islands today before decreasing to below gale force
later this afternoon. Wide swaths of near gale force winds are
expected over the western two-thirds of the Bering Sea and
adjacent coastal waters as the low moves westward.
Several shortwaves will rotate around the this low...keeping
rainfall in the forecast for most of the region through tomorrow
Long term forecast (days 3 through 7)...
a persistent large area of low pressure will remain centered over
the Bering through at least next weekend while the upper level
ridge over Mainland Alaska shifts east into Canada and flattens.
The net result will put the area into a persistent cooler and
more moist pattern...with a surface ridge along the eastern Gulf
and north Gulf Coast supporting low level onshore flow. Shortwave
troughs will periodically rotate up from the western Gulf and
eastern Bering keeping skies mostly cloudy and bringing scattered
showers...periods of rain and mild temperatures to much of
southwest and south central Alaska.
Fire weather...red flag warning...141.
Synopsis and model discussion...pld
southwest Alaska/Bering Sea/Aleutians...rf