Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
516 am akst Wednesday Mar 4 2015
Analysis and upper levels...
The diffuse highly amplified trough that started the evening over
the southwest Mainland has continued to track eastward with a weak
upper level low (and associated surface reflection as seen on
satellite and scatterometer passes) residing south of Kodiak
Island. Scattered rain showers have been observed across the Kenai
Peninsula with a few flurries falling toward northern Cook Inlet.
The ooz Anchorage sounding hinted at a decent dry layer extending
vertically to nearly 850 mb which has really limited precipitation
making it to the ground. Subsidence associated with an upper level
ridge building in the wake of the trough has created favorable
conditions for fog across southwest Alaska after the recent rain
and snowfall...with places from Dillingham to Cape Newenham up
toward Toksook Bay all reporting fog during the overnight hours.
An area of low pressure off the eastern coast of Russia continues
to make steady eastward progress toward the Bering Sea this
morning. The cold occlusion associated with the low extends south
toward Adak with a cold front trailing into the North Pacific. A
weak warm front near Nikolski continues to occlude but will likely
keep precipitation across the central Aleutian Islands as rain
initially before the colder air dives south later this morning.
Models continue to be in good synoptic agreement. All models
initialized the Kamchatka low and its frontal zone well when
analyzing surface wind speeds...the 500 mb vorticity maximum/min and
satellite images. This bodes well for the morning forecast as no
major discrepancies arise until late this week and into the
weekend with the track of a second Kamchatka low expected to skirt
the northern sea and bring a reinforcing shot of cold air to much
of Alaska. One feature of note is how all synoptic and hi-res
models are in good agreement with the trough consolidating all of
its energy as it pushes on shore on Thursday instead of fragmenting
the energy as seen in previous runs. This would potentially lead
to a decent snow event across portions of southwest and southcentral
Alaska. Overall...forecast confidence is above normal for the morning
Short term forecast southcentral Alaska (days 1 and 2)...
southerly flow continues to lift a moist relatively warm marine
air mass from the Gulf into south central Alaska this morning.
Light rain will continue to be fairly steady along the north Gulf
Coast and Prince William Sound with scattered rain and snow
showers further inland tapering off through the day. While
conditions will be stabilizing under a Flat Ridge tonight think
that stratus persisting and thickening overnight will be the more
likely result than much fog but will need watch any areas closely
that do get breaks in the clouds as the warm rather moist low
levels will be quite conducive to fog with any clearing.
The next significant incoming weather feature will be the
shortwave trough approaching from the west Thursday night and
early Friday morning. While much of the associated surface front
will have weakened and been left behind...the upper level dynamics
associated with the shortwave look strong enough to produce a fast
inch or two of snow as it crosses the area.
Short term forecast southwest Alaska (days 1 and 2)...
residual snow and rain showers will continue over the Kuskokwim
valley and interior Bristol Bay through tonight. Patchy fog will
continue each morning in sheltered areas or areas near the coast
with weak onshore flow. These showers will be continue to reside
over the region into tonight before finally being shunted east by
an approaching weather front that will enter southwest Alaska from
the Bering this afternoon. A cold upper level trough will swing
onshore Thursday and sharpen as it crosses the southwest
Mainland...bringing a brief respite before the next system arrives
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
the weakening weather front currently near the pribilofs and
eastern Aleutians will quickly track east and inland later today.
Behind this front...strong westerly winds will continue to impact
the southern half of the Bering. The next gale-force weather
system will move into the Bering Thursday morning and will race to
the eastern Bering by late Friday morning...bringing mainly rain
but there will be some snow especially along the periphery of the
main precipitation shield as it moves east. Behind the
front...scattered rain and snow showers will persist over a large
part of the Bering.
Long term forecast (days 3 through 7)...
a progressive pattern will 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
Marine...gale 173 175 176 177 178.
Heavy freezing spray 185.
Synopsis and model discussion...mc
southwest Alaska/Bering Sea/Aleutians...cirrocumulus