Heavy Freezing Spray Warning 2, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKST Fri Jan 13 2017

.ANALYSIS AND UPPER LEVELS...
There is a broad upper level trough settling in over much of
northern Alaska. Fairly strong westerly to southwesterly flow
aloft continues over the southern mainland. There is an upper
level ridge over the western Bering sea with a very thin eastward
extension into the central Aleutians. Another large upper trough
is stationed south of the Aleutians with a band of moisture that
stretches from just south of the Western Aleutians eastward into
the southern Gulf. Weak offshore flow exists at the surface over
the southern mainland, with satellite imagery from this morning
showing fog dissipating over the cook inlet region but remaining
over parts of the Southcentral interior. Current observations over
the Bering and Aleutians show Cold northerly flow and showery
conditions continuing as we move into the morning hours.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through Sunday
morning, with some minor differences in the placement of the
surface low today/tonight as it moves north-northeast into the
Prince William Sound area by Saturday morning. Small differences
in the placement of this low can create considerable differences
in the precipitation field, resulting in below normal forecast
confidence. However, with the general trend of all the models
toward the GFS and Canadian solution over the past couple of days,
one could be slightly more confident in seeing a moderate amount
of snow with this system.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through this
morning. Snow will move into the area Friday afternoon resulting
in MVFR/IFR conditions through Saturday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The radar is rapidly filling in over the Gulf of Alaska and
southern Cook Inlet as the warm front makes it way into
Southcentral Alaska. Precipitation will be all snow with the
exception of Kodiak Island and parts of the Prince William Sound
area...especially the southeastern Sound near Cordova where the
warmest air will be. Snowfall accumulations will be significant in
the mountains around Thompson Pass but winds should remain well
below blizzard criteria. However visibilities may be significantly
reduced due to snowfall rates alone. Snowfall rates in the
Anchorage bowl and Mat-Su valleys should be greatest between
midnight tonight and Saturday early morning. At this time snowfall
amounts in the Anchorage area look to be in the 4 to 8 inch range
through Saturday morning. Depending on how fast this system moves
through snow amounts could end up being higher but the 4 to 8 inch
range seems very reasonable at this time.

Cold air will move into the Cook Inlet region Saturday and bring
rather gusty south to southwest winds thought the Inlet. The strong
winds streaming through the Kamishak Gap on the west side of the
Inlet will move into Kachemak Bay. This will bring Gale force
winds into the bay and in Homer as well.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
Offshore flow will continue through Friday night as a trough
pushes through the area. As the parent low moves to the northeast
Saturday, winds over southwest Alaska will calm. The low is also
helping to bring in colder air that will last through the weekend.
Light snow is possible for areas near the Alaska and Aleutian
Ranges this afternoon and evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
Cold northerly flow will dominate the Bering and Aleutians
through the weekend. This will bring snow showers to the area as
well as gusty gap flow winds along the Alaska Peninsula. Freezing
spray will also be a concern with the exception of marine areas
around the Western Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Confidence is beginning to improve beginning Sunday that most of
the cold air moving into the Mainland will generally remain west
of the Alaska Range due to much better agreement in the placement
of the arctic trough. As result temperatures over the Southwest
Mainland late this weekend are expected to fall below, but not
well below normal as was possible only a few days ago. From
Southcentral eastward, there is now increasing agreement of a much
warmer and active pattern due to the further west placement of
the upper level trough. In particular, there is much better agreement
in recent runs of the GFS and EC in a rapidly moving and much
deeper low into the Gulf Sun-Mon. It is beginning to look more
likely that this system will bringing widespread snow and a
chance for gusty winds to the Gulf Coast and Southcentral into
early next week, however confidence is low exact impact of it. It
is also important to note that this system will likely bring
temperatures east of the Alaska Range above normal by Monday, a
large change in the forecast over the last few days.

By the middle of next the models are good agreement that the
arctic trough will begin to spread over much of the Mainland. This
setup would bring the best potential for widespread cold
throughout the area, however with the large amount of recent
variability in the long term models there is fairly low confidence
in any particular solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...GALE WARNING...119 120 125 130 131 138 139 141 155 165
170 172 173 174 175 179 180. HEAVY FREEZING SPRAY WARNING...130
139 140 141 160 165 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...MTL