Gale Warning 106, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
427 PM AKST Fri Feb 8 2019

.ANALYSIS AND UPPER LEVELS...
Today's main weather focus is on the strong front moving over the
western Aleutians and Bering this afternoon associated with a
vertically stacked low situated northwest of Shemya. Adak has
already observed rain as this front progresses eastward, along
with strong winds, which have already gusted above 70 mph in
Shemya. Looking to the mainland, the omega block pattern remains
parked over the North Pacific extending northward across the
Gulf. High pressure and dry, yet cloudy conditions have been
observed across Southcentral. Fog and low stratus continues to
linger across the Copper River Basin through Cordova. The western
side of this "dirty" (cloudy) ridge continues to pull in moisture
and warm temperatures that extend across the AKPEN and Southwest
Alaska.

&&

.MODEL DISCUSSION...West of the Alaska and Aleutian Ranges, models
are in solid agreement. This is lending to overall high forecast
confidence, especially as it pertains to the high winds and waves
over the Aleutians. The one aspect that will require some hand
editing will be precipitation type. East of the Alaska Range, it
is a whole different story. As early as tomorrow morning, models
have some fairly staunch disagreements. The NAM has a much
stronger vort max moving through the Cook Inlet area. This would
bring light snow as early as Sat morning. However, the other
models have this as just a shear axis and no precipitation for
Southcentral for Sat. Then there are further disagreements with a
larger system sliding through Sun. The NAM is much further north
with this shortwave and its associated surface low. The net effect
is more precipitation across Cook Inlet and Kenai Peninsula based
off that model. For now, the forecasters are discounting the NAM
as an outlier and hedging towards a drier solution through the
weekend.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Right near the
end of the TAF period (00z), ceilings will start to lower to near
MVFR as some light snow tries to move in from the west.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
through Sunday)...

The aforementioned large forecast model discrepancies made for a
somewhat more challenging forecast than usual this afternoon.
However, going with the consensus solution, Southcentral can
expect to continue to see mainly quiet weather. The upper level
ridge working to deflect most of the hazardous weather continues
to remain in place. However, middle and upper level moisture will
continue to move over Southcentral, keeping most areas under
mostly cloudy skies. Most of that cloud cover will remain thin
enough that the sun will be able to be seen though the cloud
cover.

During the day Saturday, there may be a few snow showers over the
northern half of the Susitna Valley as southerly flow tries to
wring out a few of those snow showers with the passage of a weak
upper level wave. A reinforcing front moving east out of Southwest
Alaska will bring steady rains to Kodiak and the north Gulf Coast
Sunday morning. While it's expected to make more eastward progress
than its predecessors, the current forecast is that it will cause
increasing easterly gap flow winds across the Chugach, which are
expected to keep most of Anchorage and the Matanuska Valley
initially dry. The front and its associated upper level support
will rapidly shear apart during the day Sunday, resulting in rapid
weakening of the feature. Thus, the most likely scenario for
Sunday afternoon is that the decay of the front will result in
rather quick diminishing of the gap winds, which will quickly end
the downsloping associated therewith. However, since the lift that
helps form the snow will also be diminishing, it appears Anchorage
and the Matanuska Valley will get only some remnant snow showers
from it with most areas currently expected to stay under an inch
of new accumulation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Rain over southwest Alaska will taper off through the evening
before more light showers move back in over the area tonight in
warm, southerly flow. Saturday evening a front will push in from
the west and will bring more rainfall to southwest Alaska. Early
Sunday morning as the front pushes further inland it will
transition the rain over to snow from west to east. Sunday
afternoon ridging will build in behind the front and clear out
most of the remaining precipitation.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Strong cold air advection around the western Bering low will
continue to bring hurricane force winds to the western Bering
through the evening. The front associated with this low is pushing
through the central Aleutians and will make it to the eastern
Aleutians Saturday afternoon. It will then continue its track to
the east and be replaced by high pressure building into the Bering
behind it. Another deep system will approach the western Aleutians
on Sunday bringing a strong push of warm air up with it.

&&

.MARINE (Days 3 through 5)...

The active storm track in the Western Bering will continue Monday
through Wednesday as low after low moves northward along the
Russian coast. On Monday, a strong storm will cross the Bering Sea
and head towards the Bering Strait. This storm will bring strong
gale force winds from the east ahead of it, while behind the
front, southerly to southwesterly gale to storm force winds will
follow. This will be a broad area of storm force winds, and it is
expected to make its way into the Central Bering on Tuesday.
Westerly winds are expected to remain near gale force through the
Bering through Wednesday, when the next storm approaches from the
west. At this time, there is some difference between on the
timing and location of the next low, but it appears to be
consistently strong, so the potential for storm force winds ahead
of the front exists for the western Bering again on Wednesday.

Meanwhile, conditions in the Gulf of Alaska appear to be somewhat calmer
than the Bering for the 3 to 5 day period. High pressure building
in beforehand will weaken the trough that crosses the Gulf on
Monday. Behind this front, northwesterly winds will increase
through the Gulf, reaching gale force through the channeled areas
and the Barren Islands, but diminishing rapidly further away from
shore. There is some uncertainty whether these northwesterly winds
will weaken during the 5 day period, or whether they will
maintain gale force through Wednesday as a low develops in the
eastern Gulf.

&&

.LONG TERM FORECAST (Days 3 through 7)...

There is surprisingly good agreement between models at the
beginning of the long term forecast for what will be an active
storm period over the next week. A strong low pressure system somewhere
around 960mb will move northward along the western Bering,
bringing strong southerly to southwesterly flow for most of the
West Coast. With this low pressure system comes a large slug of
warm air, meaning that Monday will be warm, wet and windy along
the West Coast, which will then quickly be followed by more
seasonable cold temperatures on Tuesday. Conditions east of the
Alaska Range are a little more uncertain due to the fact that the
models are having difficulty resolving the strength and location
of the low that develops in the Gulf of Alaska. At this time, it
looks like a quick shot of precipitation (snow mixing with rain
further south) in the Monday time frame, then rapidly cooling with
gusty outflow winds beginning Tuesday.

Later in the week, the forecast becomes slightly more uncertain,
due to model differences on a developing low in the Western
Aleutians beginning Wednesday. However, a developing ridge ahead
of this front promises colder temperatures across the mainland
through Friday, with the possibility of outflow winds along the
coast in the usual windy areas. As for the Bering Sea, timing may
be uncertain, but stormy conditions are expected through the end
of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Hurricane Force winds 411. Storms 185 412.
         Gales 173 175-177 179 181 413 414.

&&

SYNOPSIS AND MODEL DISCUSSION...MO/ALH
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...LF