Small Craft Advisory 190, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
430 PM AKST Fri Mar 3 2017

.ANALYSIS AND UPPER LEVELS...
There is an upper level ridge over the eastern and central Bering
Sea. There is an upper level low over the southeast Gulf of
Alaska moving to the south. North to northwest flow aloft is in
between these features over all of mainland southern Alaska and
the Alaska Peninsula. Offshore flow continues at the surface, but
is abating as the Gulf low weakens. There is an upper level low
centered to the southwest of the western Aleutians. An associated
front and large moisture plume is moving into the western and
central Aleutians into the western to west central Bering.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through the short term
portion of the forecast (Sunday afternoon). There are only minor
differences with a low moving into the western and central
Aleutians on Sunday. Forecast confidence is thus above normal.

&&

.AVIATION...
PANC...North winds will diminish late this afternoon to early
evening. VFR conditions are expected to persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sat and
Sun)...
The current weather pattern is going to hang on for a while.
Clear and cold will dominate the entire area. The one critical
element that will change some over the weekend is the wind. The
gradient and upper- level support is starting to weaken near
Valdez, so the high wind warning expiration time of 6 PM still
looks good. Winds should diminish across the entire area this
evening. This will allow most places to fully radiate out and
result in the coldest night of the past several days. By Sat, the
ridge over the Bering has reoriented somewhat bringing more
northwesterly flow rather than northeasterly. Some weak energy
will still make it over the ridge, but this time it will favor
westerly gaps such as Whittier and the Barren Islands more- so
than Thompson Pass.

By late Sat and Sun, a slightly stronger shortwave will drop from
the AK Range through the area. This should help to keep gusty
winds blowing through the gaps. Places that loose their winds will
see the coldest morning of this pattern on Sun. By Sun afternoon,
a deep arctic low will send another shortwave from north to south
through the area. We have increased winds with this feature with
this forecast update. Plenty of cold air and moderate upper-level
support will help ratchet the winds up once again through Valdez
and the Matanuska Valley. At this point, the jet does not look as
favorable as it did for earlier today. But with the number of
similarities, we will be monitoring this system for high wind
warning potential.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Partly cloudy skies with cold conditions will persist until Sat,
when a front brings some snow showers to the area. Snow shower
activity will end Sat night as the front weakens. Sunny and cold
conditions settle back over the area on Sun afternoon through Mon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A front will bring snow showers over the eastern Bering on Sat
which dissipate on Sun. A stronger front over the western Bering
will bring snow and rain showers to the western and central
Aleutians through Mon. This front will be accompanied by small
craft and gale force winds.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Expect a continuation of conditions of the last week; cold, dry,
and breezy, followed by moderating temperatures and wind by late
next week. Sunday afternoon begins the extended forecast where
the upper pattern looks identical as the one currently overhead. A
trough will continue to sit over the mainland as a ridge amplifies
over the central Bering. The cold outflow pattern will continue as
an arctic air mass gets forced through the coastal mountains,
driving the incredibly gusty winds. There is good agreement within
guidance of a shortwave trough (currently over the pole)
propagating southward over the mainland by late Sunday. The wave
will invigorate the winds around the area, possibly with more
warning level gusts in the Valdez area. Another wave comes through
the flow on Tuesday, enhancing the gradient once again.

A moderation in the pattern comes mid-week when ridging becomes
more established over the Bering Sea. There is discrepancy between
ensemble guidance and deterministic guidance on the nature of the
ridge. Confidence is high in it existing, however, in what shape
is still up in the air. Ensemble mean guidance wants to keep a
more defined ridge and even an omega block in place, while
deterministic guidance wants to beat the ridge down with
shortwaves on the north and eastern periphery. The change in
sensible weather would be a warmer and less windy airmass as
ridging builds in, but still cold/dry. Once these blocks get into
place it's hard to quickly move them out, so I'd put my money on
an established block at this point. Stay tuned.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 131.
MARINE...Gale 121 130-132 173-177 185.
		 Heavy Freezing Spray 121 129 130 138.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DS
LONG TERM...MTL