Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 161347
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 AM AKST Sat Dec 16 2017

.ANALYSIS AND UPPER LEVELS...
A sprawling upper level low encompasses the eastern Bering and
southwest mainland this morning, promoting widespread shower
activity across much of the region as broad and relatively unstable
onshore flow remains focused over Southcentral AK. A strong front
is pushing inland along the North Gulf Coast, bringing steadier rain
to coastal locations and initiating a brief push of gusty
southeast winds into the Anchorage and Palmer areas as the down
inlet pressure gradient is quickly reversed by a meso low moving
up the inlet. Farther west, more snow is beginning to mix in with
the abundant showers over the central Bering as colder air filters
into the region on the back side of the low.

&&

.MODEL DISCUSSION...
Models remain in excellent short term agreement as the low shifts
eastward into the Gulf by Sunday, continuing the recent cooling
trend across the southern mainland. Shower activity will also
trend down across the region by late Sunday into Monday as the low
pulls off to the east and transient ridging moves in behind it,
initiating a brief offshore flow regime. Attention then turns to
a strong front sweeping across the Bering from west to east on
Sunday as deep low parallels the Kamchatka coast. Primarily used
the NAM for the morning package given the strong overall
agreement, but also blended in some GFS for the next Bering system
as it depicts slightly stronger winds along the front.

&&

.AVIATION...
PANC...VFR conditions are expected to prevail through most of the
TAF period in a showery southwest flow regime, however occasional
MVFR conditions will remain possible through this evening as any
showers move over the terminal. A departing front will bring a
brief window of gusty southeast winds to the terminal early this
morning, with winds diminishing somewhat by mid morning and then
continuing to trend down through the afternoon as the pressure
gradient weakens.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper low along the west coast of Alaska will move east
through Sunday night, with its axis centered near the Kenai
Peninsula around noon Sunday, and south of Yakutat late Sunday
night. The front along the north Gulf coast will move inland and
dissipate today, with winds diminishing over most land areas.
Showers will continue over southern Alaska as the trough traverses
the area. This will also usher in a colder air mass, with snow
levels dropping to the surface this afternoon and tonight. A
ridge will build into the area later Sunday and Sunday night. This
will set up an offshore flow regime at the surface, with the usual
areas (such as Whittier and Seward) seeing gusty winds. Showers
will end from west to east Sunday afternoon through Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Low pressure along the eastern Bering keeps ongoing showers across
the Southwest through Sunday night then slides across to the gulf.
Precipitation will mainly be snow with cooling temperatures
aloft, however a slightly modified air mass along coastal Bristol
Bay may bring a brief period of rain showers during peak heating
today. Gusty south winds shift to the west and north late sunday
as the surface low departs. The next front moves to the southwest
coast early Monday bringing strong southerly winds and snow as it
pushes eastward. There is still a bit of uncertainty with this
system for precipitation types, but it looks like a warmer air
mass changes snow over to rain along the much of the southwest
coast and just inland across Bristol Bay.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

An active pattern continues through Tuesday night as low pressure
over the east Bering exits to the Gulf and is quickly followed by
a stronger North Pacific storm system. The first system currently
spinning over Nunivak Island advects colder air from eastern
Russia which pushes across the Aleutians and Alaska Peninsula
tonight. Weak short waves rotating about the upper level low will
bring snow showers along the northern waters through Sunday, with
a mix of rain and snow along the southern waters changing over to
snow tonight.

The next powerful storm system moves to the western Aleutian Chain
late tonight and quickly spreads precipitation and strong gusty
southerly flow to the central Bering by Sunday afternoon.
Precipitation along the front may start as snow, however this warm
core system changes the type quickly over to rain as a strong
subtropical jet amplifies across to the northern Bering. Gusty southerly
flow continues through late Tuesday as the storm center remains
organized as it slowly fills on a northerly track toward the
Bering Strait.

&&

.LONG TERM FORECAST (Days 3 through 7...Mon through Fri)...
The weather picture for next week is starting to become clearer.
There are 2 major features to focus on. The first will be a very
deep low over the Western Bering Mon and its associated front. The
low will bottom out somewhere in the 945 mb range late Sun into
early Mon. But its trek across the Bering will impact the whole
area to start the week. Along the front, storm-force winds and
moderate rain should be expected through the Aleutian chain as it
pushes from west to east. Behind the front, expect widespread
showers (transitioning from rain to snow) and gusty winds as cold
air wraps around. As the front impacts SW AK, it will start out as
snow with some gusty winds. This could create some difficult
travel conditions, so stay tuned to this portion of the forecast.
But with warm air and onshore flow, the snow should transition
fairly quickly to rain. Today models have come into better
agreement that this feature will hold together long enough to make
it into the Cook Inlet region. If a few ingredients hold together,
this could have the making of a decent snow event for the
Anchorage area. But there is still a lot of time and variables
that have to match before there is much certainty in this
solution.

The second major feature will be a building ridge over the North
Pacific to end the week. There is still abundant uncertainty as to
exactly where this feature will establish itself. On its western
edge, it will bring moderate to heavy precipitation and warm and
windy conditions. Underneath the ridge axis, it will likely be
cold and foggy. Stay tuned to the forecast to see exactly how this
pattern unfolds and what the sensible weather will be at the
surface as we move towards Christmas Weekend.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...Storm Warning 177 178 411 413
 Gale Warning 150 155 165 170 171 172 173 174 175 176 179 185
  412 414

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CB
AVIATION...CB
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...MSO



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