Small Craft Advisory 97, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKST Tue Jan 28 2020

.ANALYSIS AND UPPER LEVELS...
A broad long wave trough extends south across the mainland and
phases with a short wave over the southern Gulf of Alaska. A
strong southerly jet (120Kt plus), associated with a rapidly
occluding surface low in the southern Gulf of Alaska, is evident
by a pronounced dry slot on satellite imagery to the south and
east of the surface center. Satellite imagery also shows a well
defined occluded front associated with the low. Cold northerly air
flowing off the Southwest Mainland is evident by open and closed
cell cumulus over the eastern Bering Sea and eastern ALeutians.
Strong and gusty winds squeezing through the gaps in the Alaska
Peninsula are depicted by cloud streets south of the Alaska
Peninsula. Cold temperatures and gusty northerly winds continue to
produce low wind chills across Southwest Alaska.

&&

.MODEL DISCUSSION...
Models on synoptic scale are in generally good agreement in the
short term. They struggle though in the evolution and movement of
the occluding surface low and developing triple point center.
Timing and placement will affect winds and precipitation
potential.

&&

.AVIATION...
PANC...VFR conditions should persist through tonight. North winds
will increase this evening and stay fairly gusty through tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A storm force low has entered the southern Gulf this afternoon,
which will continue to be the predominant weather driver across
Southcentral for the next few days. A Blizzard Warning has been
issued for Kodiak Island starting this evening for high winds,
heavy snowfall and reduced visibility through tomorrow evening.
Areas near Kodiak City could receive snowfall totals of 9 to 18
inches.

As the low over the Gulf moves farther north, a barrier jet will
set up along the north Gulf coast, intensifying the pressure
gradient. This will increase winds for Seward and the Valdez area.
Thompson Pass will also see stronger winds in this pattern, which
has led to a Blizzard Warning being issued for this area starting
tonight through Wednesday afternoon. Winds will be the driving
factor, causing whiteout conditions at times, with only a few
inches of new snowfall accumulation.

The low will align just right that snow will develop tonight and
continue through Wednesday from Portage Valley through Turnagain
Pass. This alignment will allow for a Turnagain Arm wind to set up
across the area which will be responsible for bringing ample
moisture for another round of snow, which will be moderate to
heavy at times, into the area. A Winter Storm Watch has been
issued from Wednesday afternoon through late Wednesday night for
possible blizzard conditions as the snow and wind will increase in
intensity during this time. 4 to 8 inches with locally higher
amounts are possible in conjunction with the strongest winds that
could gust as high as 45 to 60 mph. Total snow amounts through the
duration of the event - tonight through Wednesday night - of 12
to 24 inches are expected.

Warmer temperatures are expected across areas of Southcentral,
however, most precipitation looks to remain frozen with the
potential for a short switchover to rain for Cordova. The backside
of the low sees arctic air wrapping into it which looks to end the
warm temperatures as soon as Thursday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Arctic high pressure persists over northern Alaska, maintaining
strong northeast winds and cold, clear conditions over much of the
southwest Mainland. A Wind Chill Advisory remains in effect for
the Kuskokwim Delta and Bristol Bay area through Thursday. A low
approaching the Gulf Wednesday will bring an increase in cloud
cover and an increase in winds, particularly for the interior
Bristol Bay/AKPEN area. Expect a slight warm-up from the increased
cloud cover and easterly flow, but winds will ramp up in
conjunction with the warm up, so hazardous wind chills remain
possible. Precipitation from the low will generally be focused on
the south side of the Alaska/Aleutian range. That said, as the low
drifts into Cook Inlet and occludes late Wednesday, moisture
wrapped around it should overrun cold air in place in the
Kuskokwim Valley/interior Bristol Bay area. This could bring
prolonged light snow to the middle to lower Kuskokwim Valley and
the Alaska Range foothills (generally east of Koliganek and
Igiugig) late Wednesday into Thursday. Precipitation will diminish
Friday as a ridge builds over the Bering, stabilizing conditions.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Arctic high pressure persists over northern Alaska, maintaining
strong northeast flow and cold air advection over the Bering and
Aleutians. This setup, in conjunction with a low in the Gulf, is
causing enhanced gap winds through the eastern Aleutians. Gap
winds will likely gust to storm force late tonight and Wednesday
into Thursday, as general flow backs to NNW and geostrophic winds
peak. South of the eastern AKPEN (i.e., from Chignik east), gusts
could flirt with hurricane force late tonight, as the Gulf low
deepens. Periods of ocean-effect snow will persist over the Bering
Sea, Pribilof Islands and Aleutians for the next few days as cold
air flows over the warmer waters of the Bering. A Winter Weather
Advisory remains in effect for blowing snow along the AKPEN
through Wednesday evening, and highest snow accumulations will be
on the peaks, but given the expected winds it won't take much snow
to limit visibility's in low-lying areas. Ocean-effect snow will
continue to impact Unalaska, but temperatures will be a bit warmer
than the AKPEN and winds won't be quite as strong thus advisory
level conditions are not expected at this time. Meanwhile, high
pressure over eastern Siberia maintains a relatively warmer air
mass over the western Bering and western Aleutians. Though snow
will continue in the central and western Aleutians, significant
impacts from blowing snow are unlikely. A strong low will approach
the western Aleutians from the southwest Friday.

&&

.MARINE (Days 3 through 5...Friday through Sunday)
Gulf of Alaska: Persistent low pressure is expected to remain in
the Gulf through Saturday. While the easterly winds along the
northern Gulf coast will taper, strong northwesterly flow will
persist through the usual gaps and passes, especially over
Kamishak Bay and Wide Bay south of Kodiak Island through Saturday.
By Saturday night, a strong front enters the western Gulf. Gales
are likely with this front, and storm force winds are possible.

Bering Sea and Aleutians: Gusty northerly flow will taper over the
eastern Bering by Friday morning. A weak low in the northern
Bering may spread some gales in over the Pribilof Islands and
northward as it lifts to the north and exits the Bering by
Saturday morning. Attention shifts to a strong ~960 mb low moving
over the western Aleutians Saturday morning. Gales are expected,
though there is increasing confidence in storm force winds with
this system. Models have not settled on the track of this low,
though it is likely to impact the Bering through early next week.

&&

.LONG TERM FORECAST (Days 4 through 7...Saturday through Tuesday)
The persistent upper level trough that has been in place over the
Gulf will eventually shift eastward as an upper level ridge
approaches Saturday. There is increasing confidence in a strong
area of low pressure entering the Bering/western Aleutians
Saturday morning. Models are hinting at a sharp temperature
gradient forming over the Bering late Saturday into Sunday, which
could potentially fuel the development of several additional areas
of low pressure. Depending on if these lows form, and where they
track, there remains potential for a pattern change across
southern Alaska for early next week as warmer southerly flow
advances eastward.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 131 171.
 Blowing Snow Advisory 181.
 Wind Chill Advisory 155 161.
 Winter Storm Watch 125.
MARINE...Storm Warning 119 120 130 131 138.
 Gale Warning 127 128 132 136 137 139 150 155 165 170>174 179 180.
 Heavy Freezing Spray 121 127 130 138 139 141 150 155 165 170>172
179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...CK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...KO