Small Craft Advisory 106, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
525 AM AKST Wed Feb 1 2017

.ANALYSIS AND UPPER LEVELS...
The pattern continues to amplify this morning. The jet moves north
from the North Pacific at approximately 125 kts into the Western
Bering Sea. It then climbs up and over the building ridge at 135
kts before diving back through Bristol Bay at 85 kts. A 70 kt
finger of the jet continues to help support the decaying front
that is stretching north to south across Cook Inlet this morning.
The front kept precipitation fairly steady overnight across the
Western Susitna Valley, but radar is starting to reveal signs that
it is weakening. Thus, we have allowed the Winter Storm Warning to
expire. Broad, moist onshore flow across places from Kenai over
to Cordova are keeping rain and snow showers going along the
coast. Over the southwest portion of the mainland, the building
surface high pressure has allowed widespread freezing fog to form
in many places. Some of the fog is dense enough to put down an icy
coating in isolated locales. Over the Western Bering, a storm
force front is blasting through the Western Aleutians bringing
rain and some 30 foot seas.

&&

.MODEL DISCUSSION...
All models are locked on to the ridge that will build over the
mainland and direct the weather for the next several days. The
NAM was relied upon tonight for its higher resolution. The details
that are uncertain is exactly how strong the offshore winds will
be as the ridge establishes itself. And then, depending somewhat
on those winds, when and where the low stratus and fog will
materialize. The clouds and fog will also have a big impact on
temperatures depending on where it develops.

&&

.AVIATION...
PANC...As the front over the area falls apart today, the showers
along the mountains will also dissipate. VFR conditions will
persist through the daylight hours with northerly flow. There is
considerable uncertainty in the development of some fog and/or low
stratus tonight. The primary concern is that it would advect in
from the Knik Arm. Thus, have trended the forecast in that
direction.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The pattern change over Southcentral Alaska is getting underway
today as the upper level trough is moving eastward and the upper
level high is pushing into the interior of the state from the
west. This will taper off the snow showers over the area starting
with inland areas this morning and then they should end over the
northern Gulf this afternoon or evening. As skies clear the
biggest forecast question will be whether there will be widespread
areas of fog that develop. The most likely area will be around
Cook Inlet with the Copper river basin also becoming susceptible
by tomorrow. A warm upper level ridge and the corresponding
inversion set the stage for fog. The mitigating factor will be the
northerly winds that will also develop and whether that will be
enough to keep it at bay.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The upper level ridge is positioned along the Southwest Alaska
coastline extending southward through the Eastern Aleutians.
Therefore, fog and low stratus is the predominant weather
phenomena this morning. The Nighttime Microphysics satellite
imagery was showing a large swath of fog over the Kuskokwim Delta
extending southward just over Cape Newenham before streaming into
the Eastern Aleutians from Nelson Lagoon eastward to Pilot Point.
The aforementioned satellite imagery was also showing areas of fog
in the Lower Kuskokwim Valley east of Sleetmute this morning. Look
for visibilities of one quarter of a mile or less at times in the
Kuskokwim Delta region, Cape Newenham, and along the Eastern
Aleutians from Nelson Lagoon eastward to Pilot Point this morning.
The offshore flow has kept Dillingham from receiving any dense fog
that has developed in the different areas of the Southwest Alaska
region this morning. Look for the offshore flow to strengthen in
the afternoon today, and will inhibit any development of fog for
the Thursday morning time-frame.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The storm force occluded low just west of Shemya continues to
track towards the Kamchatka Peninsula. The associated front
continues eastward before stalling over the central Bering/Aleutians
by late tonight. By Thursday another North Pacific low tracks
southwest of the Western Aleutians with the frontal boundary
moving through the aforementioned region by Wednesday afternoon.
This brings warmer temperatures accompanied by gusty gale/storm
southeasterly force winds to the Western Aleutians, and the
Bering.

&&

.LONG TERM FORECAST (Days 3 through 7)...
There remains good agreement that a blocking pattern setting up
over the mainland late this week will bring a period of quiet
weather to much of the Mainland through this weekend. A weak ridge
associated with this blocking pattern has shifted a little further
to the east due to a stronger shortwave trough rotating around
the western edge of it. The result of this is a slightly warmer
forecast from Southcentral into the Copper River Basin, along with
weaker outflow winds than initially expected. This setup will
also put Cook Inlet closer to the ridge axis, which would be more
favorable for fog/low stratus development. This was left out of
the forecast however as the down inlet flow (while a bit weaker)
should be enough to limit significant fog development, but this
will need to be monitored in the coming days. Over the Western
Bering little has changed as stationary frontal boundary will
bring nearly persistent gale force winds with rain to much of the
area from late this week into the weekend.

Forecast confidence then quickly diminishes by early next week as
significant model disagreement in the track and intensity of both an
upper low moving developing over the Mainland and a polar low over
the Beaufort Sea. The exact track of these features will has a
significant impact in the forecast looking into early-mid next
week, especially with regards to temperature.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm Warning...173 175 176.
         Gale Warning...170 172 174 177 178 179 185.

&&

SYNOPSIS AND MODEL DISCUSSION...MO
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DK