Gale Warning 234, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
920 AM AKST Wed Mar 6 2019

.ANALYSIS AND UPPER LEVELS...

The upper level pattern over southern Alaska is becoming more
progressive with time as a series of upper level waves moves over
the area. A longwave ridge is slowly moving eastward along the
Alaska-Yukon border. A weakening shortwave trough is currently
over southwest Alaska, helping to slowly move the surface front
eastward with time. Shortwave ridging is moving across the central
Bering as another large upper level trough digs southeastward over
the far western Bering.

The current Anchorage sounding shows a nocturnal inversion at the
surface underneath a nearly moist adiabatic sounding above that.
The cloud cover is the result of the aforementioned surface front
very slowly moving eastward over Southcentral. A new area of low
stratus over the Bering is moving into Southwest Alaska, resulting
in much lower ceilings over that area. Over the Bering, weak high
pressure associated with the low stratus is being moved eastward
by a strong low and associated leading front. The center of the
storm force low is currently approaching the western Aleutians, as
the leading front and associated rainfall move through Adak and
Atka.

&&

.MODEL DISCUSSION...

The models are in very good agreement overall as they have been
in lockstep the past several days with tracking the big lows and
their associated fronts as they move across the Bering. The
NAMnest was the model of choice once again owing to its higher
resolution of terrain features.

A front moving across the western Gulf Thursday night is causing
some disagreement in the models in regards how it interacts with
a rapidly changing upper level pattern at the time. The American
models latched on first to the front developing into a rather weak
low as it moves near Kodiak City late Thursday night, while the
foreign models took until the latest runs to depict a closed low.
This posed some challenge with the current forecast package. Other
than that feature and tracking the fog and low stratus across the
area, forecast confidence remains above average.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Late this
afternoon into tonight, a weakening disturbance will move through
which will increase the chances of flurries or light snow showers
to move across the airport. None of the snow is expected to
become heavy or last very long.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Ridging has broken down over the area making way for a trough to
swing through from the west. This trough will bring precip to
western portions of Southcentral Alaska, with the highest amounts
along the southern Kenai Peninsula and locations west of Cook
Inlet. It should also be cold enough for the majority of
locations to see snow for any new precipitation. The trough will
push off to the east tonight leaving lingering showers behind
before another trough moves in Thursday from the south. As this
second trough approaches it will spin up a low near Kodiak Island
Thursday evening, however there are some discrepancies amongst
the models on its location and intensity. This will factor into
the timing and location of precip moving into Southcentral
Alaska.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...Brief
ridging will maintain dry conditions into tonight, with patchy fog
possible around sunrise over much of Southwest, especially the
Kuskokwim Delta coast and Bristol Bay areas. The front associated
with a low currently approaching the western Aleutians will reach
the mainland Thursday morning, bringing increased winds and
precipitation. Though winds will predominantly be from the south
or southeast, expect precipitation to be mainly snow Thursday
morning. Areas of blowing snow are possible, but with expected
temperatures in the upper 20s Thursday morning, do not expect
classic advisory level conditions. As the front pushes inland and
dissipates, precipitation will transition to a rain or rain/snow
shower pattern Thursday afternoon. Cold air wrapping around the
backside of the low could change precipitation to predominantly
snow Thursday night into Friday...but QPF will generally be light.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...A storm
force low centered roughly 150 miles southwest of Attu and its
associated front will continue to impact the Bering Sea and
Aleutians. Winds briefly gusted to over 70 mph in Adak overnight.
Widespread gales with embedded storm force winds along the front
will continue today. The front is currently situated over the
central Aleutians, and as it continues its trek eastward
precipitation types will transition from snow to rain. As the low
moves to the northwest tonight into tomorrow, expect another swath
of storm force winds in cold air wrapped around the backside of
the low. High seas will persist as well... in particular, swell
originating from the heaviest swath of winds could push wave
heights above 40 feet south of the Rat Islands. Another storm
force low will approach the western Aleutians Friday, bringing
another round of precipitation and increased winds. While the
strongest winds should be concentrated to the south, out of the
Aleutian coastal waters, areas of gales are likely in the coastal
zones.

&&

.MARINE (Days 3 through 5)...
A large area of low pressure will move into the Bering Sea over
the weekend, closely following the low anticipated to move in
later this week. An increase in sea ice coverage is possible along
the west coast late Sunday behind this second low. Meanwhile, a
series of two lows will also move northeast into the Gulf of
Alaska; the first being Friday and the second on Sunday. This
means active weather and small craft to gale force winds for both
areas through the weekend. Confidence is high we will see active
weather and winds. However, confidence is low on the exact
placement of low pressure systems and winds surrounding them as
model guidance is erratic in the long term. This is detailed in
the long term forecast. Overall, gale force winds in the Bering
and Gulf of Alaska can be expected this weekend, with the forecast
needing to be honed further.

&&

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

The long term time frame starts Friday with a low in the eastern
Bering and a low in the Gulf of Alaska. As we continue into the
weekend, the active weather pattern continues as another round of
low pressure enters the Bering. Broad low pressure will encompass
the Bering and southwest Alaska and continue into early next
week. A low is expected to spin off this area of low pressure and
move into the northern Gulf of Alaska, which should bring some
weather to southcentral Alaska.

Models are in general agreement on this pattern, especially that
broad low pressure will be present in the Bering. However, models
are not doing well handling the specific placement of lows entering
the Bering and Gulf of Alaska. There is a considerable difference
between the GFS and other models for the low entering the Bering
this weekend, with the GFS favoring one stronger low and other
models resolving features with two lows. Placement is also an
issue with models for the low entering the Gulf of Alaska early
next week. So, we know there will be an active weather pattern
for all of our forecast area. However, due to large inconsistencies
between guidance on systems, confidence is low as to exactly how
the weather will play out in the long term.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 155 165 170 171 172 173 175 176
		       178 179 180 181 185 413 414.
		 Storms 174 177 411 412

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...BB