Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
405 PM akst Thursday Jan 29 2015
Analysis and upper levels...
A high amplitude upper level ridge over the Bering Sea is the
strongest feature over the forecast area. An upper level low
still remains well south of the Alaska Peninsula with a weak
trough extending out of it over southcentral Alaska. This
pattern is producing fairly strong north to northeast flow
aloft over the eastern Bering Sea and southwest Alaska with
weaker southerly flow along the north Gulf Coast with southcentral
Alaska under very weak flow aloft.
At the surface the strong high persists from the central Bering
Sea through northern Alaska. The main surface low is a complex
system well south of the Alaska Peninsula with a front extending
south of the Alaska Peninsula through the north Gulf Coast. A low
has also developed along the front in the northwest Gulf of Alaska
which is enhancing lift over the Gulf coastal regions. The pressure
gradient north of this front remains fairly strong especially over
the Bering Sea region.
Model initialization was very good again across the spectrum of
the main models. The one feature that rapidly diverges is the low
that is west of Attu and moving northward. The speed and strength
of this low vary quite a bit starting tonight. However this
feature will remain far enough west that only the far western
Bering Sea and Aleutians will be impacted by it.
While the synoptic features of the GFS European model (ecmwf) and NAM are very
similar the GFS and European model (ecmwf) look to be dong a better job with the
precipitation amounts and therefore snow amounts in southcentral
Alaska. The main issue is the NAM is much heavier with the snow
amounts over the southcentral area. The GFS and European model (ecmwf) are more in
line with what is in the forecasts. The reason the NAM looks to be
too high is due to the amount of dry air in place already in
southcentral Alaska...as well as the model just showing too much
moisture through the atmospheric column. Therefore the lower snow
amounts of the GFS and European model (ecmwf) were used as model guidance.
Short term forecast southcentral Alaska (days 1 and 2)...
A frontal zone over the northern Gulf Coast will continue to make
slow progress northward this evening...spreading clouds and
moisture into inland areas. Light snow will impact locations from
the Copper River basin to the mat valley southward to Anchorage.
The eastern Kenai Peninsula will also see light snow
accumulations...with more scattered showers toward the western
Kenai. Continued strong northerly outflow winds through mountain
passes will continue tonight...with some local areas of blowing
snow through Thompson Pass. Blustery wind chills will remain
through all favored mountain passes.
High pressure will begin to settle over the region during the
afternoon hours Friday...with rapid clearing developing by Friday
night. Outflow winds will begin to increase once again Friday
evening as a North Pacific low tracks toward the Gulf of
Alaska...but some local areas of patchy fog will be possible as
high pressure aloft builds in. A return to clear and pleasant
weather will resume region wide Saturday...with the exception of
a few showers over Kodiak Island.
Short term forecast southwest Alaska (days 1 and 2)...
A persistent Bering Sea high interacting with a low south of the
akpen will keep a moderate pressure gradient across SW Alaska. Northeast
wind with cold and dry conditions across the region will begin to
moderate on Sat as the Bering ridge begins to weaken.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
Disturbances moving around the low south of the akpen will keep
windy conditions over the akpen and the eastern half of the
Aleutians through Sat. Another disturbance will bring a chance of
rain to these locations on Sat. A weather system skirting the
western Bering at the end of the week will bring a chance of rain
to the western Aleutians Friday night into Sat.
Long term forecast (days 3 through 7)...
Much of the region will continue to be dominated by a dry
offshore flow pattern through the early part of next week with
high pressure over the Mainland and a North Pacific low well south
of the Alaska Peninsula near 50 degrees north latitude. This will
continue to support gusty outflow winds along the Gulf Coast with
a favorable pressure gradient in place and very cold air filtering
out of the Copper River Basin. A chance of snow then returns to
the forecast by middle to late week as models are hinting at an
Arctic trough digging over the southwest Mainland from the Chukchi
Sea...which would also result in a return of much colder temperatures
over the southern Mainland.
Marine...Gale Warning 127 132 138 150 155 170 171 172 173 174 176 180.
Heavy freezing spray warning 127 160 180.
Synopsis and model discussion...ez
southwest Alaska/Bering Sea/Aleutians...ds