Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 101644 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
744 AM AKST Fri Jan 10 2020

.ANALYSIS AND UPPER LEVELS...

Clear and very cold conditions continue from the Copper River
Basin west to the Kuskokwim Valley as a 1036 mb ridge extends
across the Alaska Interior. Overnight temperatures have once
again dropped to -30F to -45F over the Copper River Basin and
upper and middle Kuskokwim Valley. Over the Susitna Valley,
temperatures have largely been dependent on winds, with overnight
lows ranging from -15F to -30F for Palmer, Skwentna, and Willow
(where winds have been calm) to 0F to +10F for Talkeetna and areas
north of Wasilla (where winds of 10kts or greater have persisted).

Snow has come to an end overnight for Kodiak City as a front
associated with a 979mb low over the southern Gulf tracks
southeast. The pressure gradient between this low and the interior
ridge is keeping winds quite gusty across the Southcentral coast,
especially through gaps and passes (e.g. Valdez, Passage Canal,
Seward, Thompson Pass).

Low clouds and areas of light snow remain across coastal Southwest
as an occluded front continues to fall apart as its tries to push
east. Infrared satellite imagery also shows a deepening 964 mb
low lifting north across the western Aleutians with a warm and
cold front extending from the center of circulation across the
southern Bering and central Aleutians. The latest ASCAT
scatterometer pass indicates a wide area of gale-force winds,
as well as some embedded storm-force winds, wrapping around both
this low and a second occluded 972 mb low west of this first
system. Warmer air is also being advected north across the central
Aleutians with temperatures climbing into the mid 40s for Adak
and Atka. Snow has returned to Shemya as colder air wraps back
around the backside of the low.

&&

.MODEL DISCUSSION...

Models are in good agreement with the overall synoptic pattern
across the area over the next few days. High resolution models
continue to be favored with respect to the local effect gap
winds. By Sunday, the NAM diverges from the other deterministic
models, trying to not only progress a front further east across
the state, but also spinning up a triple point low over Bristol
Bay and moving that low over the interior, eventually developing a
new low in the northern Gulf. Other guidance slows the track of
the front and keeps any low development south of Kodiak Island and
movement of this feature across the southern Gulf. Thus, the NAM
was discounted in favor of the GFS for any updates to the forecast
by day three.

&&

.AVIATION...

PANC...VFR conditions and light winds are expected to persist.
However, there is still some fog lingering over the northern half
of Knik Arm, and it is possible, given the light and variable
winds, fog may drift far enough south to impact the airport
complex. Confidence in this scenario is very low. Thus, VCFG
remains in the forecast.

&&

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

An occluded front from a parent low over the western Bering looks
to spin off a triple point low southwest of Kodiak Island late
Friday night into Saturday morning. This frontal system will take
a similar track to the low we saw earlier this week, in that it
will stay well south of the north Gulf coast. The difference,
however, is it looks to make a southeastern progression across the
Gulf and move quite rapidly. After a lull in gap winds, this
frontal system will tighten pressure gradients once again along
the north Gulf coast. This combined with the cold arctic air in
place over the Copper River Basin will increase winds out of bays
and passes: Resurrection Bay, Whittier, the Valdez waters and the
Copper River Delta through Saturday. A Wind Chill Advisory
remains in effect for Thompson Pass through Sunday at 10 AM AKST
as winds and cold air persist.

The passage of this frontal system sets up favorable pressure
gradients to produce a Matanuska Valley wind. The cold air sitting
in the Copper River Basin also contributes to this wind. Based on
observed winds yesterday, Palmer has managed to stay out of the
gustier conditions, with winds headed westward across portions of
Wasilla. This makes sense since most of the pressure gradient is
stacked up north and east of Palmer, and there is nothing to force
the wind southward as it exits the Matanuska River Valley. Thus,
winds have been updated to reflect this general wind pattern for
today.

High pressure remains over mainland Alaska that will continue to
bring sub-zero temperatures to most of Southcentral through the
weekend. The overall increase in winds across the region (not
necessarily at the surface, but in the low levels) has eroded much
of the fog that has been in the Anchorage area the past week.
However, the threat of fog could return as the low level flow
lightens up over the weekend. The Copper River Basin would be
another favorable area to watch for fog.

&&

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

Snow showers will begin to taper off along the Southwest coast
from Toksook Bay to Pilot Point through the morning hours as an
occluded front dissipates. However, there will be a short period
of calm conditions across the Southwest before the next warm front
approaches the Alaska Peninsula late morning and then into the
into mainland by this afternoon. This quick moving, well
organized front will bring widespread snow extending across the
Kuskokwim Delta through Bristol Bay, which could bring a few
inches of snowfall across the region. As this feature moves inland
overnight into Saturday afternoon, the front will weaken as snow
showers continue over the Kuskokwim Valley and eastern portions of
interior Bristol Bay.

Southwest Alaska will have another quick break in snow before a
second front moves in late Saturday afternoon into through Sunday.
This system should also bring a few inches of new snowfall to
interior locations, which will still see temperatures well below
the freezing mark. Temperatures across the region will continue
to be on an upward trend throughout the weekend as these warm
systems keep moving in, with coastal locations and the Alaska
Peninsula likely to see temperatures near or slightly above the
freezing mark. This will keep any precipitation in these areas as
rain or a rain/snow mix.

&&

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

A storm force low positioned near Shemya this morning will
continue to lift northward through late tonight, keeping strong
winds and high seas stretched across much of the Bering and
Aleutian Chain. The strongest core of storm force winds will
remain over the western and central Bering through Saturday
morning. Widespread rain and snow showers will also accompany this
system as it continues into the northern Bering through Saturday.

A weak, yet fast moving surface low will move from the North
Pacific to the central Aleutians near Dutch Harbor by Saturday
afternoon, which will bring an area of gale force winds with it.
This feature will then move into the Southwest mainland by Sunday
morning. Strong winds will continue across the entire domain
through Sunday afternoon when a period of quiet conditions moves
into the area.

&&

.MARINE (Days 3 through 5)...

Sunday into Monday a weak surface low develops and tracks east
across the southern Gulf of Alaska. This will bring gusty northerly
winds across the western waters which may be gale force if the low
deepens more than currently progged. For the Bering on Sunday,
westerly gales start the forecast along the northern waters which
taper down Sunday night. The next North Pacific front moves to the
western and Central Aleutians Monday night bringing max gales winds
and rain across the western waters through Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Below normal temperatures and dry conditions continue for much of
the southern mainland in the forecast Sunday through next
Thursday. Gusty offshore flow along the gulf also persists as the
dominant ridge across the interior resides over the the Alcan.
The most active weather focuses over the Bering as new upper level
parent develops over the North Pacific moves to the Kamchatka
Peninsula Sunday night. This gale force systems front maintains
strength as additional energy propagates around the base of its
trough mid week. The southwestern areas of the state are expected
to trend slightly warmer at the beginning of next week as a
subtropical air mass advects northward...however, temperatures
will remain below normal.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...

PUBLIC...Flood Warning 121.
 Wind Chill Advisory 131.
MARINE...Heavy Freezing Spray Warning 119 121 126 127 128
     129 130 139 185.
         Storm Warning 411 177 178.
         Gale Warning 121 127 128 412 413 414 155 165 170
         171 172 173 174 175 176 179 180 181 185.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...CK/SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KH



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