Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 300111
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 PM AKST Tue Nov 29 2016

.ANALYSIS AND UPPER LEVELS...
The large upper level low remains over the Arctic Ocean northwest
of Barrow. A trough extends southeast from the low over the
mainland part of the state and into the northeast Gulf of Alaska
where it is interacting with a strong surface low in that area.
This strong low combined with high pressure over the interior of
the state is producing strong outflow winds along the north Gulf
Coast and Prince William Sound.

A second trough extends over the central Bering Sea where it meets
up with a surface low located a little southwest of Adak this
afternoon. This low will elongate as it heads east-northeast
through tomorrow night.

&&

.MODEL DISCUSSION...
Like yesterday, the models are in good agreement with the synoptic
scale elements but there are still some more subtle differences
that will impact the forecast. This has been the case with the low
in the northeast Gulf which has tracked slightly farther eastward
than expected which pushed the snowfall along the north Gulf
Coast and Copper River Basin farther eastward today. The biggest
issue for the region will be the way the low, which is currently
in the ALeutians, elongates over the northwest Gulf of Alaska
Wednesday and Wednesday night. While it is a small difference, the
amount the warm front pushes to the northwest over the Kenai/Chugach
Mountains and into Cook Inlet is a key factor. The ECMWF and GFS
models push the front into Cook Inlet which will put the main area
of snowfall over the Inlet and Northwestward. The NAM and most
recent Canadian model run stall it out over the Kenai and Chugach
Mountains putting the snowfall over the Kenai Peninsula and
northward toward Anchorage.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through the
night.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An impressive storm force Gulf low is moving inland toward the
ALCAN this evening but will rapidly weaken through the remainder
of evening. Strong offshore coastal pressure gradients will
rapidly weaken...along with associated gap winds. There is some
blowing snow along with very light falling snow through Thompson
Pass, but with the sharp drop-off in winds expected, any
significant blowing snow conditions will rapidly diminish this
evening. Otherwise, another cold night is in store as arctic air
remains entrenched and skies clear tonight. A fast moving warm
front will then quickly track toward the North Gulf Coast
tomorrow, bringing easterly coastal winds and coastal rain/snow.
With the front stalling along the coast, downslope flow will
remain mostly dominant across inland locations, but it will
remain cold enough for all snow, most of which will be rather
light and sporadic west of the Chugach Mountains/Kenai Mountains.

Closer to the coast, snow will quickly change to rain or a
rain/snow mix as the front moves inland, but places along the
coast such as Cordova may experience a brief burst of moderate
snow along with strong east-southeast winds before changing over
in the evening. For Valdez and Thompson Pass, snow may be heavy
at times through Thursday, with the possibility of periodic
changeovers to rain in Valdez Thursday night and Friday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The ridge across north central Alaska remains stationary as low
pressure pushes across the Western Aleutian chain to the Alaska
Peninsula Wednesday afternoon. This approaching system tightens
the pressure gradient between the two systems which increases
winds tonight, mainly for the Kuskokwim Delta and the Western
Capes. Gusty conditions persist through Thursday morning and then
tapers down as the surface low slips southeast of the Alaska
Peninsula. A front moving ahead of the Aleutian surface low brings
increased chances for snow along the Aleutian Range Wednesday and
into Thursday. Otherwise, dry conditions prevail under offshore
flow across the Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Low pressure along the Central Aleutians moves a gusty gale force
front across the central Bering this evening with the eastward
edge of the boundary progressing across the Alaska Peninsula. The
surface low center pushing the front tracks due east across the
Central Aleutians to the Alaska Peninsula on Wednesday, then takes
a southeast turn toward the Gulf early Thursday. An unsettled
weather pattern continues for the Bering on Thursday as an upper
level disturbance dives from Kamchatka and another surface front
moves into the Western Aleutian chain.

&&

.LONG TERM FORECAST (Days 3 through 7...Fri through Tue)...
There is growing confidence that some snow could reach inland to
the Cook Inlet Region late Thu into early Fri. Another low will
develop along the polar jet axis down over the Gulf of AK. This
low will then wrap some more moisture over areas from the Kenai
Peninsula through the Matanuska Valley. While it certainly does
not look like much in the way of accumulation at this time on
the lee side of the Chugach, any mention of snow in this very dry
pattern is note-worthy. The set-up is quite convoluted, which
only further muddles the details.

Beyond the late week snow threat, be prepared for the coldest
temperatures of the season this weekend. As the aforementioned
low moves toward SE AK, some more energy will dive from the Seward
Peninsula into the base of the longwave trough over the Gulf.
Then a ridge building over the Bering will serve to reinforce
very cold, dry air moving over the AK Range and into Southcentral
AK. Clouds could help to keep the bottom from falling out, but
skies should clear by Mon allowing for the coldest morning of the
2016 winter.

The cold air will also help to usher in some impressive outflow
winds. Typical places like Thompson Pass, Whittier, and the Copper
River Delta could see very strong gusts. But gaps along the AK
Range will likely see the strongest winds with gusts approaching
hurricane-force as they blast into Shelikof Strait.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 131.
 Wind Chill Advisory 155.
MARINE...Heavy Freezing Spray Warning 121 129 140 160 180 181.
         Gale Warning 119 120 125 130 131 138 139 150 155 160 165
  170 172 173 174 175 176 177 178 179 180 181 185.


&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MO



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