Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
534 am akst Tuesday Feb 9 2016
Analysis and upper levels...
A powerful North Pacific jet stream remains the main driver of
sensible weather across southern Alaska as lows originating from
it continue to March across the Gulf before moving inland. One of
these such lows...now rapidly weakening...is currently moving
through southwest Alaska off the Kuskokwim Delta coast. A large
trough is now developing across the North Pacific with its center
south of Unalaska. This trough is anchoring the aforementioned
North Pacific jet around 35n latitude. With a strong western
America ridge in place...this is keeping the persistent pattern
featuring North Pacific lows moving north into the Gulf of Alaska and
southern Alaska. Another system is beginning to develop this
morning in the vicinity of 44n 143w... and this low and associated
front will move into the Gulf of Alaska by this evening...and the
northern Gulf Coast by Wednesday morning.
Otherwise...precipitation is rather spotty across southwest Alaska
largely owing to a downslope component of the low level wind.
Showers across southcentral are largely relegated to the upwind
portion of the Alaska Range...chugach...and along the Kenai
Peninsula. Otherwise...drier air and a down inlet pressure
gradient are keeping inland southcentral dry.
The models are in excellent agreement with the large scale
pattern through next week. They are in overall good agreement with
the general depiction of a series of North Pacific lows moving
into the Gulf of Alaska through Friday...but they do begin to
diverge with the second and third lows Thursday and
Friday...respectively. With that said...while the tracks and
timing are different in the varying models...the overall sensible
weather impacts are not much different...so forecast confidence
remains moderately high.
Short term forecast southcentral Alaska (days 1 and 2)...
as the previous front continues to fade...showers along the north
Gulf Coast will also diminish through the day. Weak ridging will
then build in until early Wednesday when another front pushes
into the area from the south. Similarly to the last front this one
will also have a warm push with it bringing rain and snow to the
north Gulf Coast and Kodiak Island. However...with the parent low
staying to the south combined with downsloping conditions due to
southeast flow at mountain top...the majority of the precipitation
will stay on the Gulf side of the coastal ranges. The low moving
up towards the Gulf tonight will also aid in outflow winds around
the southcentral that will last into Wednesday.
Short term forecast southwest Alaska (days 1 and 2...Tuesday and
one low will exit to the northwest through the day today
leaving the area under the periphery of the Arctic high and
increasing offshore flow. First though...a few lingering snow
showers associated with that low will clip through the Ahklun
Mountains and the coast of the yk-Delta. After this...northeast
winds will start to increase and bring dry conditions for just
about all areas through Wednesday. The winds will be strongest along the
western convective available potential energy and the coastal areas on Wednesday.
Yet another low will brush up against the Pacific side of the
akpen late Wednesday into Thursday. It will sling a front into the Aleutian
Range...but the orientation of it will keep just about all inland
areas from seeing much precipitation. It will reinforce the
northeast winds though.
Short term forecast Bering Sea/Aleutians (days 1 and 2...Tuesday and
the area will be dominated by two low pressure systems. One
is currently south of Dutch Harbor and will continue to weaken. It
is bringing gale-force easterly winds and some decent rain to the
eastern and central Aleutians. Counter-clockwise flow around the
low consumes the rest of the Bering Sea with numerous rain and
snow showers. The next low is currently tracking toward the akpen.
It will "steal" the energy from the afore mentioned low and
effectively "re-orient" the counter-clockwise flow. By Wednesday
afternoon the center of circulation will be south of Sand Point.
Gale-force east to northeast winds will spread over the eastern
Bering and the far eastern Aleutians with colder air and snow
showers dominating further west.
Long term forecast (days 3 through 7)...
Not much change in the synoptic weather pattern is expected over
the next 7 days as the upper level trough that has been anchored
over the Bering Sea and northern Pacific shows no signs of
dissipating. Several strong upper level lows and shortwaves will
drop into the North Pacific off the eastern coast of Russia
through next weekend which will help re-invigorate the longwave
trough and keep the weather pattern similar to that observed over
the past month. Models are in surprisingly good agreement through
the extended period and it appears unseasonably warm temperatures
will continue through southwest and southcentral Alaska. The
placement of the longwave trough keeps the Gulf of Alaska and
southcentral Alaska in the main storm track. Normally for this
time of the year...this could be a favorable set up to bring
snowfall to southcentral Alaska. However...the amplified trough
will bring low pressure systems for the subtropics up toward
Alaska and advect warm and moist air into the Alaska Mainland
(more favorable for rain across most locations). Temperatures
across south central will be well above normal with a lot of
locations seeing near or above freeing temperatures while southwest
Alaska will see temperatures anywhere from 5 to 15 degrees above
normal through the extended.
Marine...storm 132 138 150 352
gale 119 120 127 130 131 155 160 165 170 171
172 173 174 180 351
freezing spray 185
Synopsis and model discussion...ja
southwest Alaska/Bering Sea/Aleutians...MO