Ashfall Advisory 1, NWS Anchorage, AK

137 
WWAK72 PAFC 221308
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
408 AM AKST Thu Nov 22 2018

AKZ181-221900-
/O.EXT.PAFC.AF.Y.0001.000000T0000Z-181122T1900Z/
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
408 AM AKST Thu Nov 22 2018

...ASHFALL ADVISORY NOW IN EFFECT UNTIL 10 AM AKST THIS MORNING
FOR PERRYVILLE...

* LOCATION...Along the coast near Perryville.

* ASHFALL...Trace amounts to less than one quarter of an inch of
  ash.

* TIMING...Now through mid morning. 

* IMPACTS...Persons with respiratory problems may have  
  difficulty breathing when outside. Electronic devices may be 
  damaged if not protected. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

An ashfall advisory means that ash will be deposited in the
advisory area. People in areas of ashfall should seal windows and
doors. Protect electronics and cover air intakes and open water
supplies. Minimize driving. Listen to your radio station for
further information.

Please report any observations of ashfall to the Alaska Volcano
Observatory by calling 907-786-7497 or visiting
https://www.avo.alaska.edu/ashfall/ashreport.php.

&&

$$

975 
WWAK72 PAFC 221902
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
1002 AM AKST Thu Nov 22 2018

AKZ181-222015-
/O.EXP.PAFC.AF.Y.0001.000000T0000Z-181122T1900Z/
Alaska Peninsula-
Including the cities of Cold Bay and Sand Point
1002 AM AKST Thu Nov 22 2018

...ASHFALL ADVISORY HAS EXPIRED FOR PERRYVILLE...

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKST Wed Nov 21 2018

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low is traveling southeastward from Mekoryuk
Island to the Lower Kuskokwim Delta. A negatively tilted, long
wave trough extends over mainland Alaska and over the entire Gulf
of Alaska. At 300 mb, the jet stream is oriented northwesterly-
southeasterly over the eastern Aleutians with a 120 kt streak
skirting the Aleutian chain. Increased vorticity is present in the
area of the low and the jet streak over the eastern Aleutians. A
front is moving over the western Aleutians which can be observed
in satellite imagery. Sandwiched between the long wave trough and
the incoming front, a ridge is quickly building over the Bering
Sea. The Bering remains relatively cloud free with mostly cumulus
present under the ridge and corresponding surface high pressure.
Stratus is making its way into the western Bering with the
associated front. Mainland Alaska is generally covered in stratus
and scattered precipitation as seen on radar imagery. In the
northern Gulf of Alaska, the low is in its final stages of
occlusion as it moves inland over eastern Prince William Sound.
Northerly flow continues to increase across the mainland advecting
a deep layer of cold air over the northern and western parts of
the state. Patchy clearing over Southcentral is leading to
increased surface cooling causing fog to persist for locations
along the the Cook Inlet/Kink Arm this morning. Thus, the Dense
Fog Advisory will continue for Anchorage through noon on
Wednesday.

&&

.MODEL DISCUSSION...

No major model discrepancies were noted in the short term with
decent consensus on the significant features impacting the area.
Some fairly significant differences begin to show up by the
weekend with the arrival of the next major system into the Gulf of
Alaska from the North Pacific. The NAM seems to be the outlier
right now as it depicts a 975 mb surface low moving north over
Kodiak Saturday morning with an associated front pushing across
the Gulf Coast later in the day. The EC/GFS are in better
agreement and keep the low out over the southern Gulf with a later
arrival of the front to the coast. The current forecast leans
towards the later solution.

&&

.AVIATION...

Dense fog is expected to persist through most of the day today
with little change in the overall pattern expected. There could
be some temporary improvement and lifting of the fog later this
afternoon but weak winds and a strengthening surface inversion as
ridging builds in from the west will promote fog redevelopment tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Stable conditions across the Anchorage Bowl/Kenai Peninsula have
given rise to fairly widespread fog. Little changes
atmospherically tonight in these areas so we may see a repeat
performance. Gusty northeasterly winds are expected over the
Matanuska Valley today and tonight, so any fog around this morning
is not likely to reappear tonight. Light snow will continue
across the Copper River Basin into the early afternoon hours. Snow
accumulations should be fairly light. Patchy fog will likely
develop in that region overnight with decreasing upper cloud
cover.

A weakening surface low retrogrades west today the dissipates
tonight. An upper level low center moves from the Southwest
Mainland to south of the Gulf tonight. In response, a broad
inverted surface trough will setup over the Gulf and encompass
several small low centers. The net effect will be increased
offshore flow with local gusty gap winds across the north Gulf
Coast and brisk northwest winds over the western Gulf. These
conditions should diminish later Thursday.

&&

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

Snow develops across Bristol Bay this morning as a surface low
slowly slides southeast to the Gulf. The upper level low driving
the front may initiate a few showers through tonight as it shears
apart. Patchy fog should improve tonight as subsidence mixes dry
air down to the surface ahead of an approaching Bering ridge. A
dry cold air mass advects across the region tonight through Friday
night bringing colder than normal temperatures for the end of the
week.

&&

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

Snow showers will develop along the eastern Bering through the
afternoon as an upper level shortwave overhead elongates on the
backside of a closed low, which exits southeast later today.
A cold dry air mass vies for dominance across the Bering
as it drops southward behind the exiting low; meanwhile, a strong
warm front pushes across the western Aleutians. The colder air
mass begins to lose its hold tonight as the subtropical jet pushes
the warm front eastward. This front will bring gusty gales along
with rain as the boundary undercuts the cold air mass across the
southern Bering; although a brief period of mixed precipitation is
possible at the onset. The front progresses to the Alaska
Peninsula and the Pribilof Islands Thursday night with a mix of
rain and snow along the boundary as it slows and re-organizes
through Friday.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

A series of fronts and areas of low pressure are expected to
impact Southern mainland Alaska and will make for a warmer,
cloudier, and wetter second half of the Thanksgiving holiday
weekend. A front over the southern and central Gulf Saturday
morning will initiate the process of warming temperatures and
returning the area to a wet pattern. The front will track
northward into the north Gulf Coast by Saturday evening. As the
warmer air moves in, downsloping will likely help to keep
Anchorage and the surrounding areas drier, though perhaps not
entirely precipitation-free. The downsloping will also help to
quickly scour out any cold air as well. A second front will follow
right on the heels of the first for Sunday. However, by then the
models are in disagreement as to how quickly that front will move
through the Gulf into Southcentral. This is largely due to
disagreements on the track and strength of a much stronger 950 mb
low which will be centered near the Alaska Peninsula Sunday
morning. This low is likely to remain nearly stationary or follow
a looping pattern around that area, which in turn will keep
southerly flow of warm air moving into southern mainland Alaska
while winter-like cold air remains well out west over the Bering.
This pattern is likely to persist through much of the rest of the
final week of November, which will keep the area much more wet and
icy than snowy.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory 101.
MARINE...Gales 170 172 173 174 175 176 177 178 411 413 .

&&

SYNOPSIS AND MODEL DISCUSSION...KVP/RA
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...JW