Small Craft Advisory 109, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 AM AKST Thu Feb 2 2017

.ANALYSIS AND UPPER LEVELS...
A stout upper level ridge over the west coast of Alaska is
evolving into a sprawling closed high this morning as it is
undercut by a potent shortwave retrograding northwestward towards
the AK Peninsula. This high pressure is promoting tranquil
conditions and clear skies across the mainland, with modest
outflow winds over favored areas along the gulf coast. The
combination of residual low level moisture and light low level
winds beneath the building high is contributing to patchy fog
development across the Cook Inlet region and portions of the
northern gulf coast, which represents the primary forecast concern
for the morning forecast package. Meanwhile, the shortwave is
poised to bring showers and gusty southeast winds to the Akpen and
Eastern Aleutians today as it rapidly tracks into the Bering.
Farther west, a decaying frontal boundary is bringing rain and
gale force winds to the central Bering.

&&

.MODEL DISCUSSION...
Models show excellent agreement into the weekend as high pressure
remains the dominant weather feature in the short term. Continued
to utilize the Hi-Res NAM for its handling of localized wind
effects and also the depiction of precipitation associated with
the disturbance currently tracking into the Bering. All guidance
has shifted slightly farther west in the past 24 hours with the
front entering the Western Aleutians tonight, and therefore
adjusted timing of this feature accordingly.

&&

.AVIATION...
PANC...Patchy fog will linger over parts of Upper Cook Inlet and
the Knik Arm through mid to late morning, keeping the possibility
for occasional visibility reductions at PANC through the 18-20z
time frame. Otherwise, VFR conditions and light winds will persist
through Friday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The warm upper level ridge building over Southcentral Alaska will
keep all precipitation away from the area the next few days. Most
of the region will see clear skies with this pattern with the only
departure from this expected in the Cook Inlet area where there
will be some fog that develops. The northerly winds should help
keep down the amount that develops, but with the strong inversion
and warm air aloft it does set the stage for fog. There is a
chance some fog or low stratus could develop in the Copper River
Basin as well, but this looks less likely that the Cook Inlet
area and has been left out of the forecast at this point. Some
gusty northerly winds will persist into Friday along the North
Gulf coast in the usual locations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Thu and Fri)...
A robust area of high pressure continues to establish itself over
mainland AK. Meanwhile, a moderate shortwave is starting to trek
from the Gulf of AK towards the Bristol Bay area. These two
synoptic features are working in tandem to increase the offshore
pressure gradient. This offshore flow has strengthened enough
this morning to prevent much fog from forming. There is still some
low stratus hanging on in the lower Kuskokwim Valley, but we are
doubting that it will be able to hang in much longer with so much
dry air being advected in. The high pressure will remain the
dominant force through the forecast period. It will keep
conditions dry with clear skies. The one tricky part to the
forecast is the temperatures. As the high settles in, 850mb
temperatures will continue to warm as air sinks in the upper
levels. However, offshore flow will reinforce colder air at the
lowest levels. Thus, expect slightly cooler temperatures over each
of the next few days.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Thu and
Fri)...
One front occluded front stretches from the Central Aleutians up
through Eastern Russia while another will approach the Western
Aleutians later today. The first front is slowly weakening and
drifting to the west ever-so-slightly. It is still packing some
gale force winds, but those will drift out over the Bering Sea by
this evening. There is a thin swath of steady precipitation along
the front as well. While some of the Central Aleutians have
reported rain, colder air will cause the precipitation to turn to
more of a mix or just all snow by tonight. Tonight will also see
the stronger shortwave rotating from Bristol Bay around the
periphery of the ridge and into the Central Bering. This should
result in some rain and snow showers tracking from the AK
Peninsula up through the Pribilof Islands through Fri morning.
Gusty southeast winds will accompany these showers as well.
Finally, the front approaching the Western Aleutians will bring
gale-force winds to them by this afternoon. It will also bring
another round of steady rain and snow to Western and Central
Aleutians through Fri.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning late this week there remains very good agreement that a
blocking ridge setting up over the Mainland will bring sunny
skies throughout the area (with the exception of the Bering
Sea/Aleutians) into this weekend. The main concern from this
pattern will be for the potential for fog and stratus development
and outflow winds along the Gulf Coast. At this point it appears
that the strongest winds should occur from Eastern Prince William
Sound into the Copper River Delta where the strongest pressure
gradient will be able to tap into the available cold air in the
Copper River Basin. It is also very clear that Southcentral
temperatures under the blocking ridge will be typical for strong
inversions this time of year, with temperatures falling below
normal in the valleys while rising to near-above freezing along
higher elevations.

By early next week the models are beginning to come to a consensus
that the shortwave rotating around the blocking ridge will descend
into the Mainland as it strengthens, causing cold air to move back
into the region through the middle of next week. This trough will
remain very dry however, meaning chances of precipitation appear
to be very limited for much of the mainland into the middle of
next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray Warning 160
         Gale Warning 173-178, 411, 413, 414

&&

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
LONG TERM...DEK