Small Craft Advisory 120, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
858 AM AKST Wed Feb 8 2017

corrected typo

.ANALYSIS AND UPPER LEVELS...
An upper level low over the eastern Bering is working to break
down the ridge that has resided across the state for the last several
days. To the west of this system, a stationary North Pacific low
has a front extending along the western Aleutian Chain to the
Kamchatka Peninsula with a long stream of moisture continuing to
stream up from 40N. At the surface, a pattern change is slowly
arising as a trough forms in the northern Gulf along with a second
trough just off the Kuskokwim Delta. Snow and rain showers are
developing around these systems early this morning.

&&

.MODEL DISCUSSION...
Models are in good agreement through the short range forecast into
Saturday morning, however they are mainly focusing precipitation
development along the best dynamic alignment. The challenges
through Friday will be stronger offshore winds and precipitation
associated with the upper low that traverses from the eastern
Bering to the Gulf. The NAM was preferred for the package as it
provided the best details for local edit areas.

&&

.AVIATION...
PANC...LIFR visibilities are expected to improve this afternoon
with a shift in the weather pattern as low pressure develops
across the northern gulf. A low VFR stratus deck and light
northerly flow sets up this evening through the end of the TAF
package. There is some uncertainty with snow development tonight
and Thursday as a shortwave slowly moves in from the eastern
Bering. Only flurries are expected, however updates may be needed
if the system moves in faster than expected.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Fog across the Anchorage Bowl and the northern Cook Inlet will
diminish throughout the afternoon. An upper level disturbance
dropping south toward Kodiak Island and a surface low moving into
the northern Gulf will bring increased chances of snow across
Southcentral tonight and into Thursday. Inland areas, including
the Anchorage Bowl and Mat-Su valleys, will see flurries/light
snow with little accumulation. Coastal locations will see
measurable snowfall, but not significant amounts. Another upper
low drops south Thursday night keeping chances of snow fairly
high along the North Gulf Coast and Copper River with chances
elsewhere inland. Outflow winds are expected to increase across
the eastern Kenai Peninsula and Western Gulf Thursday/Thursday
night as a surface low strengthens over the northern Gulf.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A deepening upper level trough moving along the coast will
continue to bring areas of light snow to much of the Southwest
today. Accumulations from this snow is still expected to remain
very minor less than an inch expected through tonight. The one
exception to this will be along the Bering coast of the AK Pen
where snow will linger into Thursday, which along with upslope
flow should allow for a few inches of fresh snow. Cold air will
then move back into the area late Thursday as a cold upper level
trough descends from the interior, producing below normal
temperatures that will continue into Friday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Snow showers from the developing upper level trough moving down
the Southwest coast will spread into the AK pen by this evening,
mostly to the Bering Coast. These showers along with increasing
northwesterly winds will also create areas of blowing snow to the
Bering Coast through Thursday. However with no transportable
snow currently in the area only a few inches of fresh snow this
is not expected to significantly reduce visibilities.

Over the Western Bering, a weakening storm force front currently
moving through the Western Aleutians will bring rain and strong
southeasterly winds through this evening. This front will then
stall out as it interacts with ridging over the Central Bering,
bringing persistent clouds and a chance of rain into Friday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A cold longwave trough over interior Alaska will begin to drop
down over Southern Alaska Friday morning, bringing colder
temperatures to much of the region through Sunday. As this colder
airmass settles in over the area Friday, a surface low over the
Gulf of Alaska begins to strengthen and move over Prince William
Sound. There is good agreement in the models and higher confidence
in precipitation developing along the Northern Gulf coast areas
and over parts of the Copper River Basin Friday and into Saturday.
However, models are still struggling with the positioning of the
upper level low and various surface features, which has lead to
lower confidence in snow potential over the Anchorage, Mat-Su
Valleys, and Western Kenai areas. One can say with high confidence
that several areas of low pressures will move into the Gulf of
Alaska this weekend through the middle of next week, but
confidence is low in the exact track of them.

Out west, a pattern change will also be underway over the Bering
Sea and northern Pacific, as the receding high pressure over the
areas gets pushes westward by the above mentioned cold longwave
trough tracking through the mainland. This will make way for the
upper level trough to set up over the Bering Sea and Northern
Pacific by early next week, with multiple systems at the surface
mainly staying along or south of the Aleutian chain through the
middle of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 178.
         Gale 130 150 176 177.
         Heavy Freezing Spray 180.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...TP