Gale Warning 275, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Wed Apr 5 2017

.ANALYSIS AND UPPER LEVELS...
A large upper level low circulation is centered over the Gulf of
Alaska with multiple centers embedded within. A single deep
surface low over the southern Gulf is drifting westward while an
occluded front, which extends eastward from the low center,
rotates northwestward across the northeast Gulf. A robust upper
level wave is driving this front toward Southcentral and these
features will play a key role in the weather over Southcentral
later today/tonight.

The bulk of rain with this system is falling across the western
Gulf and Kodiak Island, with lighter rain in the Prince William
Sound area as well as over the Alaska Peninsula in Bristol Bay.
An upper level trough axis and deformation zone extends from the
Gulf low northwestward across the southern Alaska Peninsula and
eastern Bering. This continues to produce steady snowfall along
the Alaska Peninsula from about Port Heiden southward. Strong
northwesterly winds also continue, with much stronger gusts
through channeled areas. King Cove Airport has observed wind
gusts as high as 77 mph.

Out west, a weak cold core low crossing the southern Bering is
producing a few showers along the Aleutians. Upstream, satellite
imagery shows a long front sweeping eastward from the Kamchatka
Peninsula into the western Bering.

&&

.MODEL DISCUSSION...
Numerical guidance is in excellent agreement with handling of
large scale features over the next couple days. One change, which
all solutions indicate, is a farther west track of the Gulf low,
passing south of Kodiak Island on Friday. There has been a
westward shift in the track of the Gulf low by all solutions, so
this will be reflected in the latest forecast. Overall forecast
confidence is high, though the rapid movement of the occluded
front across Southcentral this evening poses some challenges for
the wind forecast.

&&

.AVIATION...
PANC...Persistent easterly flow across the Kenai and Chugach Mtns
will largely keep PANC in a downslope hole with light winds and
fairly high VFR ceilings. The exception will be about a 3 hour
window approximately 05-08Z when a vigorous low level front/upper
level wave crosses overhead from east to west. Confidence is low,
but there may be a very brief period of stronger southeast winds
and lower ceilings (but remaining VFR) during this window.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The short term forecast will continue to focus around the very
slowly weakening low tracking towards the Southwestern Gulf. A
wave rotating around the northern edge of this low will bring a
surge of gusty winds to the north Gulf Coast and Turnagain Arm
this evening. These winds however are not expected at this point
to move into the Anchorage Bowl however, strong down Cook Inlet
flow should keep any Turnagain winds safely over northern Cook
Inlet. This wave will also bring another round of rain throughout
the Gulf Coast, especially to Kodiak Island where strong and
moist onshore flow will continue. Further west on the lee side of
the Chugach/Kenai mountains, downsloping most areas cloudy but dry
for most of the work week.

Winds over the North Gulf will then begin to slowly diminish on
Thursday and Friday as the low continues to dissipate just south
of Kodiak Island. Precipitation will continue however under
persistent southeasterly flow with cyclonic flow aloft, beginning
as rain on Thursday becoming snow on Friday as snow levels fall.
For Kodiak Island, rain and easterly flow will continue through
work week as the low slowly dissipates to the south.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The lower Southwestern Gulf has a 969 mb this evening that
continues to gradually track just southeast of Kodiak Island
becoming almost stationary by Friday. This results in wrap-around
moisture spilling over the Aleutian Range, Alaska Peninsula, and
extending into the Eastern Aleutians. Therefore, a showery regime
remains through the aforementioned region as we head into the
weekend. The Kuskokwim Delta, and the Lower Kuskokwim Valley will
have some precipitation this evening as some moisture spills over
from the Alaska Range. By Friday the Y-K Delta, and the Lower
Kuskokwim Valley has drier conditions due to the offshore flow.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The Western Aleutians has a gale force low approaching from the
Kamchatka Peninsula region with an associated front entering the
region by this evening. This system tracks to the southeast before
crossing the Central Aleutians into the North Pacific by Friday
morning. Meanwhile, the Eastern Aleutians continues with gusty
northwesterly winds. This synoptic feature combined with the
moisture spilling over from the low located near Kodiak Island
will produce areas of blowing snow along the Eastern Aleutians
through Friday afternoon. Otherwise, the central/northern Bering
will be under the influence of northerly flow heading into the
weekend. By Friday afternoon the Western Aleutians has a storm
force low approaching with the associated front entering the
aforementioned region by Friday Evening. This brings southerly
winds accompanied by warmer temperature resulting in a wintry mix
through the Western Aleutians.

&&

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

Beginning the extended forecast period Friday night, there will be
a high latitude blocking high over the Beaufort Sea and a gale
force low over the Western Bering Sea. Southcentral will be under
the influence of weak upper level troughing centered over Western
Alaska with an associated surface low near the Alaska Peninsula.
With the main Pacific storm track remaining well south of the
mainland, the challenge will be the interactions of weakening
lows moving into the NE Gulf of Alaska then merging with the
preexisting trough across Western Alaska. It does seem that this
will keep at least some clouds across the inland areas with slight
threats for precipitation, more so Sunday and Monday. Expect
temperatures to be near to slightly above normal as the general
pattern remains onshore.

Middle of next week there is growing uncertainty with the general
large scale pattern, but models are beginning to hint at a
shifting storm track into the Bering Sea with an amplifying NE
Pacific Ridge. Both the latest deterministic GFS and ECMWF are
hinting at a series of Bering lows shifting a trough axis/front
into Western Alaska. Should this happen, expect widespread rain
and warming temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 119. Gales 120 125 129 130 131 132 138 139 150 155
                          178.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...DEK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...JA