Small Craft Advisory 1009, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
614 AM AKST Sat Dec 26 2020

.ANALYSIS AND UPPER LEVELS...There is a weak surface low (988 mb)
entering Prince William Sound this morning with moisture wrapped
around producing an organized signature on the Middleton Island
radar. There is a major low (945 mb) in the North Pacific. Out
west the jet core that is driving the strong front has an
estimated intensity of 150 knots. On ASCAT (Advanced
Scatterometer) gales were detected south of Cordova and both gale
and storm force winds were detected south of Attu Island and
Shemya. Additionally, there is a low north of Bethel and Hooper
Bay and the remnants of a low near Dillingham. These two features
are still producing snow showers which have been detected by the
radars at Bethel and King Salmon.

&&

.MODEL DISCUSSION...Model consensus has emerged with the synoptic
pattern from the Bering to the North Pacific and the Gulf Of
Alaska. There are minor differences with the intensity of the
surface low in the North Pacific but all the models are
advertising a juggernaut with a widespread tight pressure
gradient and a widespread precipitation shield. There is a weak
low moving into Prince William Sound and and area of troughing
over the Cook Inlet. The forecast thermal profile of the boundary
layer is slightly different with each model which will impact the
snow level in the Chugach mountains.

&&

.AVIATION...
PANC...30-60 percent POPs (probability of precipitation) were
forecast for the Anchorage Bowl from 12z today to 9z Sunday. The
radar is actively being monitored. The potential for the cigs to
drop at PANC is credible. Amendments will be made to the TAF at
PANC as needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Saturday through Monday)...

Low pressure is moving into the Prince William Sound area. It is
well observed on satellite and the Middleton Island RADAR. While
the this low has been expected, models are still having difficulty
handling the track right up to its arrival. Therefore, some last
minute adjustments were made to its course tonight, bringing the
low center a little farther west through Prince William Sound.
So some minor tweaks for the weather in the area. The Blizzard
Warning for Thompson Pass is still in effect, with gap winds
through other areas as well. A little more westward track sending
some light precipitation in Anchorage, so the forecast was adjusted
there to include some light snow. This low will move quickly inland
and is still anticipated to bring snow to the Susitna Valley.

After this low exits, weather is quiet for a short while until
Sunday, when the next front moves northeast through the Western
Gulf. This will bring high winds and rain to Kodiak and
gaps/passes and through the Kennedy Entrance. Turnagain Arm wind
and winds on the hillside of Anchorage Bowl will also increase
ahead of this front. Beyond Sunday, model guidance does not agree
well at all for weather in the gulf, where each of our major
models have major placement differences for the next low pressure
system. So, low forecast confidence for coastal areas Monday with
changes in the forecast sure to come. Weather looks quiet for
interior areas of Southcentral to start the week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A shortwave trough and associated weakening surface low over
Southwest Alaska will continue to produce areas of light snow
showers today. These showers will diminish through the afternoon
hours, however, as both features lift northeast over interior
Alaska. A ridge centered over the eastern Bering will then slide
across the region later today, weakening as it does. This ridge
will then be quickly replaced by a strong frontal system tracking
toward the coast by early Sunday morning.

Southerly winds will quickly increase ahead of and along the front
as it moves across the AKPEN late tonight and to the coast for
Sunday. Precipitation along the front will initially begin as a
brief period of snow for most places along the AKPEN and Bristol
Bay. However, warmer air ushered in by storm-force southerly winds
will quickly scour away any cold air in place at the surface,
changing the snow to rain. For locations along the Kuskokwim
Valley and Delta, much colder air is place. Thus, the snow that
develops will stick around longer before changing to a mix of rain
and snow by Sunday night. The combination of strong winds and snow
along the Kuskokwim Delta coast will make for blizzard conditions
from very early Sunday morning through around noon. A Blizzard
Warning is in effect for this area. Elsewhere, snow and blowing
snow may also briefly reduce visibilities to one half mile for
Dillingham and Togiak before the snow changes to rain around mid-
morning. As the front pushes inland, the precipitation will become
more showery in nature, with mixed rain/snow showers eventually
changing back to all snow showers by Monday afternoon as colder
air works back in.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A storm-force low with hurricane-force wind gusts is tracking
northeast toward the Rat Islands this morning. Ahead of the low,
a front is moving across the southern Bering and central
Aleutians. Storm-force winds and widespread precipitation is
associated with this front with rain and gusty winds already
impacting Adak and Atka. Rain and gusty winds will overspread
Dutch Harbor by mid-morning and Cold Bay and Saint Paul by the
afternoon, where wind gusts could approach 60 mph. With some
colder air in place, precipitation over the eastern Aleutians and
Pribilofs could start as a brief period of snow. Any snow that
does fall will be accompanied by very strong winds and could
reduce visibilities to one half mile for these locations before a
changeover to rain.

Farther west, snow and blowing snow continue for Attu and Shemya,
where hurricane-force gusts have been reported overnight. A
Winter Storm Warning remains in effect for Shemya through mid-
morning when the strongest of winds is expected to diminish.

By Sunday, rain and continued gusty, southerly winds, will
encompass much of the Bering as the low stalls over the southern
Bering. A shortwave wrapping around the main low will spin up a
polar low that will bring another round of very strong winds to
Shemya. Precipitation type remains the question though, as
slightly warmer air looks to work in with this next system. Rain
and snow showers will remain over the Bering through early next
week as the low remains in place and weakens.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska: There is increasing confidence in a low tracking
from the North Pacific into the western Gulf on Monday, with a
front crossing the Gulf waters. This will likely produce at least
gale force winds Monday through Monday night, with good potential
for at least a small area of storm force winds. Confidence is low
for Tuesday through Wednesday, though the pattern will remain
favorable for one or more additional lows to move up from the
Pacific.

Aleutians/Bering: Expect a series of gale to storm force lows to
track across the region MOnday through Wednesday. It's hard to say
where individual storms will track, but most, if not all of the
Bering Sea/Aleutians/Southwest Alaska waters will be impacted.

&&

.LONG TERM FORECAST (Days 3 through 7: Monday through Friday)...

Upper level troughing extending from the Bering into the North
Pacific moves through the Gulf next week, fizzling out as it
pushes to the North Gulf Coast. Multiple shortwaves propagating
off a strong Bering low cross south to north across the Southwest
Monday through Wednesday, resulting in bands of precipitation
across the AKPEN and the Mainland. By mid-week the gradient
weakens, transitioning from a closed low to a high amplitude
trough feeding into a North Pacific low. There is weak surface
reflection with this, thus, impacts are expected to be minimal.
The next system of concern will be for a strong low developing
West of Shemya late next week. There is high model discrepancy
with this, where the EC/Canadian models want to move the low to
the north near the Kamchatka Peninsula and become relatively
stationary, while the GFS takes a straight shot eastward into the
Southern Bering. The GFS solution is also significantly stronger,
bringing widespread strong, gusty winds to much of the Bering,
Aleutian Chain and Coastal Southwest, and a leading front that
could result in widespread precipitation across much of the
Mainland, with heaviest likely located along the AKPEN.

High pressure dominates the upper levels across Southcentral
through late next week. A short-lived weak surface low tracks
north across the Western Gulf early next week, dissipating as it
crosses the Barren Islands, resulting in some possibly gusty down
Inlet flow.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155 131.
Winter Storm Warning 191.
MARINE...Hurricane Force Wind Warning 178. Heavy Freezing Spray
181. Storm 119 411 412 413 414 150 155 160 165 170 172 174 176 179
180 185. Gale 127 130 131 132 136 137 138 351 352 171 173 175 177
181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BJB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...MK/KM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
322 PM AKST SAT DEC 26 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0321 PM     SNOW             POTTER VALLEY           61.06N 149.76W
12/26/2020  M1.4 INCH        ANCHORAGE          AK   TRAINED SPOTTER

&&

CJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
337 PM AKST SAT DEC 26 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0335 PM     SNOW             2 MILES ESE POTTER HILL 61.08N 149.78W
12/26/2020  M1.3 INCH        ANCHORAGE          AK   PUBLIC

&&

CJ