Small Craft Advisory 184, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
358 PM AKST Wed Mar 1 2017

.ANALYSIS AND UPPER LEVELS...
There is a deep upper level low over the Gulf of Alaska. A compact
surface low is centered over the northwestern Gulf and moving
towards the south. An upper level high is over the central Bering
Sea. Strong northerly flow aloft is over the eastern Bering
through southwest Alaska and the Alaska Peninsula to eastern
Aleutians. At the surface, offshore flow exists over most of
southern Alaska, strongest through south central Alaska gaps.
There is a low south of the western Aleutians that is moving
slowly towards the east northeast. A front associated with this
low stretches across the central and western Aleutians and
southwest Bering Sea.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through the short term
portion of the forecast. There are some differences in surface
lows over the Gulf of Alaska, but these are mainly just outside
of our forecast area. Forecast confidence is thus higher than
normal.

&&

.AVIATION...
PANC...VFR conditions will persist. North winds will continue,
with occasional fluctuations in strength.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The forecast looks pretty steady state for the next couple days
with continued cold and breezy conditions, except for the north
gulf coast where breezy can be replaced with downright windy (if
that even covers it). An upper level low continues to spin in the
Gulf of Alaska, which will keep the mainland in this cold,
outflow pattern. Temperatures and winds continue to be the most
difficult forecast elements as clouds and precipitation will be at
a minimum for the short term. Last night saw spotty decoupling of
the surface with some places, losing wind and having their
temperatures plummet, i.e. Glennallen or east Anchorage, while
others in the Matanuska Valley or around Cook Inlet, retained wind
and higher temperatures. Tonight's lows look much the same, there
should be enough wind and mixing around stopping temperatures
from dropping in most places while others will go calm and cold.

The more interesting weather feature is an uptick in outflow winds
as the mid-upper level flow becomes more favorable along the north
gulf coast. Combine the more favorable northerly flow with a cold
pool of air in the Copper River Basin, you have the recipe for a
High Wind Warning. Cold advection through the gaps and over the
mountains will keep winds elevated through Friday morning at
warning levels, but will still remain pretty gusty through late
Friday at least.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
With high pressure dominating the Bering Sea, dry, cold, and
northerly flow will continue over southwest Alaska through Friday.
The exception to the dry conditions will be on Thursday when a
weak shortwave pushes through the area bringing light snow showers
to higher elevations. Winds look to stay gusty until Friday when
they start to taper off as the low over the Gulf weakens and moves
south which will weaken the gradient over southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
High pressure over the central Bering will keep northerly flow
over the eastern Bering and southerly flow over the western
Bering. This will also keep the storm track over the Western
Aleutians with the systems getting stalled by the high pressure.
These systems will bring up enough warm air to have a mix of rain
and snow for the Central and Western Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Colder and drier conditions are expected through the extended
forecast as the Bering Sea ridge blocks any organized storm
systems from the southern mainland. On Friday night the upper
ridge is forced a little further south back into the Pacific as
low pressure in the western Bering Sea, along with a second
system from the Arctic, send strong shortwaves toward the southern
mainland. A weak front which manages to undercut the ridge in the
western Bering Sea sends a front into the central and northern
Bering Sea, however it weakens rapidly as the upper wave shears
apart as it rides along the northern periphery of the ridge. The
ridge re-amplifies across the Bering Sea in the late weekend as
the energy from the shortwave flows downstream of the ridge. The
ECMWF maintained the best consistency through the middle of next
week and was the primary influence in making minimal grid updates
with this slowly evolving pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 131.
MARINE...Storm 127 230 131 132 138.
Gale 119 121 126 127 128 136 137 352 150 155 160 165 175 176 177
178 180.
Heavy Freezing Spray 121 126 127 129 130 141 150 160 165 179 180
414.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...KH