Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
455 am akdt Sat may 23 2015
Analysis and upper levels...
The amplified upper level ridge has moved slightly more eastward
but is still positioned over the Yukon territory and through the
eastern Gulf. The satellite imagery is showing low stratus clouds
in the Gulf and clear skies over the Copper River basin eastward.
On the backside of this amplified ridge...there are several
shortwave troughs tracking through the eastern Aleutians into the
southwest Alaska region. These synoptic features will be
accompanied by a large swath of moisture. The radar imagery is
showing light rain echoes in the Bristol Bay area and heavier rain
moving through the Kuskokwim Delta this morning. While...farther
upstream there is a closed low at 500 mb just north of Kiska with
a gale force low reflected at the surface positioned near 55n 174e
this morning. The associated weather front with this system is
bringing gusty southerly winds through the central Aleutians
northward into the Pribilof Islands before transitioning to more
easterly winds through the northern Bering Sea. The ascat
scatterometer wind imagery is picking up the gale force winds
associated with this weather front.
The models continue to be in good agreement with the remnant of
typhoon Dolphin through the weekend. Then by Sunday a low will
drop down from the Kamchatka peninsula and track towards the
western Aleutians. These two low pressure systems will phase into
one low by Monday. The European model (ecmwf) is trying to form a triple point low
south of Kiska...where the GFS and NAM are showing a shortwave
trough. While...over the Gulf the ridge of high pressure start to
move eastward but builds back into the Gulf by Monday. The
European model (ecmwf)/GFS were the preferred models of choice. The forecast
confidence remains well above average through the weekend.
Short term forecast southcentral Alaska (days 1 and 2)...
The longwave ridge that has brought such nice weather to much of
the southern Mainland over the last week is being forced slowly
eastward by approaching unsettled weather in the Bering Sea.
Clouds and rainfall are consolidating over Cook Inlet ahead of an
upper level trough/disturbance currently located near Kodiak
Island. These conditions will spread slowly northward throughout
the day today...resulting in a much different day than was
experienced yesterday around Cook Inlet. Rain will lag the clouds
by several hours...but will eventually work its way up to
Anchorage and the mat-su valleys by this evening and continue into
the overnight hours. By Sunday the rain will diminish to
showers...but the cloud-cover will likely hang on for much of the
day...resulting in a second day of near or slightly below normal
temperatures. Meanwhile...the Copper River basin will be far
enough northeast to squeak one more sunny and hot day in before
the clouds move in tonight. However...this will not all be good
news...as critical fire weather conditions will develop once again
this afternoon. See the fire weather section below.
The approaching weak front over the Gulf will push the existing
ridge of high pressure at the surface against the coastal
mountains today. This will result in an enhancement of southerly
winds across portions of the Copper Basin. These winds will be
stronger than previous days...likely exceeding 30 miles per hour...and when
combined with another day of sunshine and extremely dry conditions
the result will likely be an even more extreme red flag condition
day today when compared to previous days. The good news is that
clouds and even a little rain will move into the area from the
southwest tonight and Sunday...keeping relative humidity values
above critical values.
Short term forecast southwest Alaska (days 1 and 2)...
A large Bering trough will make slow eastward progression through
Sunday...with chances of rain through that period as waves of
moisture move inland. Locations downwind of the Alaska Range will
remain on the drier side given downslope drying...but that will
end tonight as the main disturbance moves through. Gusty southeast
winds will be strongest along the coast before slowly weakening
tonight. The North Pacific moisture feed largely cuts off by
Monday morning...with rain changing more to showers by Monday
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
The remnants of typhoon Dolphin continues to spin over the western
Bering...with gale force winds across the western Aleutians. A
weakening frontal zone over the Pribilof Islands and eastern
Aleutians will move east today...with a change to more showery
weather on Sunday. Another low end gale force low will move into
the western Bering Sunday night and Monday...bringing more rain
and southerly winds to the western Bering and Aleutians...with a
general drying trend across the central and eastern Bering and
Long term forecast (days 3 through 7)...
Operational models and ensembles are in agreement that the ridge
over the northeast Pacific and alcan will persist through next
week. Onshore flow along the western flank of the ridge will
bring rain to the north Gulf Coast Sun night through Monday. Shower
activity will cross the northern mountains into southcentral Alaska
through Tuesday. Brief ridge building will cut off precipitation on
Wednesday...but onshore flow will resume with coastal rain and inland
showers at the end of the week.
Low pressure will spin around the southern Bering for the next
week. Associated fronts will move to southwest Alaska before
dissipating against the ridge. This means that rain and showers
can be expected over the entire Bering and Aleutian chain through
the end of the week. Southeast flow across the Aleutian
Range will bring shower activity to much of southwest Alaska during
the same period...enhanced at times by the fronts as they decay
Marine...Gale Warning...155 160 165 175 176 177 178 180 181
fire weather...red flag warning...141.
Synopsis and model discussion...pld
southwest Alaska/Bering Sea/Aleutians...ja