Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
411 PM akst Tuesday Mar 3 2015
Analysis and upper levels...
there is an upper level low to the southwest of Kodiak Island with
a trough extending northward across southern Alaska. There is an
upper level ridge to the east...stretching south from the Yukon
territory across the Panhandle to just off the coast of the lower
48 states (conus). There is a strong low over Kamchatka with a
leading front over the the western/central Bering Sea pushing
from the western Aleutians into the central Aleutians. There is
plenty of moisture and clouds over southern Alaska...but with
weak dynamics the precipitation is mostly light and variable.
the numerical models are in good agreement through the short term
and are not causing any difficulties in the forecast.
However...the nature of the precipitation (type...as well as the
variability mentioned above) makes for a somewhat difficult
forecast. Therefore the forecast confidence is near normal.
Short term forecast southcentral Alaska (days 1 and 2)...
a persistence pattern continues through Thursday afternoon as an
upper level low continues to spin in the vicinity of the Gulf.
Weak upper waves rotating through the flow brings rain showers
along the Gulf with a mix of rain and snow inland. Winds across
the Turnagain Arm and northern Gulf become relatively light by
Thursday morning as the surface front diminishes across
southcentral. Another front moving into the southern Gulf this
evening will be low impact with mainly rain along the boundary
which remains over the water through Thursday. On
Wednesday...southeasterly winds across the Gulf back to the north
across the western Gulf behind the front moving into the central
Gulf Wednesday and then vary in direction through Thursday with an
overall weak surface pattern.
Short term forecast southwest Alaska (days 1 and 2)...
the area of low pressure currently centered over the Kuskokwim
Delta area will shift inland tonight continuing to bring a mix of
rain and snow with it. Cool advection following the system will
progressively turn more of the precipitation over to snow from
west to east tonight before ridging tapers the precipitation off
to scattered showers on Wednesday. The next frontal system will
arrive quickly thereafter...reaching the Alaska Peninsula
Wednesday afternoon and the west Mainland coast Wednesday evening.
An accompanying cold upper level trough will swing onshore
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
out in the Aleutians and western Bering...a rather active weather
pattern will continue. As the frontal system which passed Shemya
around noon continues east widespread westerly gales will build
in behind it tonight and Wednesday. Brief ridging will follow
Wednesday night turning winds more northwesterly and diminishing somewhat.
The next strong frontal system however will rapidly swing into the
western Aleutians on Thursday.
Long term forecast (days 3 through 7)...
a sharp upper trough will bring precipitation to southcentral
Alaska Thursday night into Friday as it moves quickly
eastward. A progressive pattern will then continue through the
weekend as zonal flow is established beneath a strong polar jet
spanning from the western Aleutians across the southern Mainland.
This will keep precipitation over much of the Mainland as a broad
surface low tracks across the northern Bering and moves inland
near the Seward Peninsula on Saturday...with precipitation type
remaining an issue across southcentral Alaska as daytime temperatures
hover near freezing. Precipitation should transition to all snow
by Sunday as colder air begins to advect into the region. After
that...models remain in generally good agreement that a transition
back to a more amplified pattern will take place early next week
as a deep trough digs over the Mainland towards the eastern Gulf
and high pressure builds over the western Bering Sea. This lends
increasing confidence that much colder temperatures will return to
the region next week...with gusty outflow winds developing along
the northern Gulf Coast.
Marine...gale 170 173 174 175 176 177 178
heavy freezing spray 185
Synopsis and model discussion...bl
southwest Alaska/Bering Sea/Aleutians...Jr