Small Craft Advisory 107, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
644 AM AKST Sat Feb 1 2020

.ANALYSIS AND UPPER LEVELS...
A pattern shift is underway this morning as the mature low over
the Gulf weakens while a much stronger storm system is pushing a
front to the western and central Aleutian Chain. Light snow
developed across the Matanuska Valley to the northern Kenai
Peninsula late last night on the backside of the weakening low,
however, only trace accumulations were reported. Low level clouds
around this low kept temperatures from plummeting, but cooling
trends were evidenced shortly after midnight as the low clouds
scattered out. Gusty winds increased for Kodiak during the early
morning hours with gusts reported to 43 knots. Gusty winds were also
noted across the western half of the Aleutian Chain as the next
front pushed across around midnight.

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.MODEL DISCUSSION...
Models are relatively in good agreement through the weekend,
resulting in only minor changes to the morning forecast package. The
higher resolution data from the NAM/nest was favored for the
southern mainland and surrounding waters.

&&

.AVIATION...
PANC...VFR conditions and northerly flow are expected to prevail
through late Sunday morning.

&&

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

A tightening pressure gradient and a shortwave trough dropping
down over Shelikof Strait and Kodiak this morning will keep strong
winds through this afternoon. Winds will then begin to weaken as
an upper level ridge begins to build in from the west. The
tightening pressure gradient and weak cold air advection across
Southcentral will peak late this morning, which will keep strong
winds through Resurrection Bay and Passage Canal through late this
afternoon before diminishing tonight. Dry conditions will move
across Southcentral as the upper level ridge begins to build in
across the region later today into the overnight hours.

The pattern quickly changes with a warm front moving across Kodiak
and into the Gulf by Sunday morning and will continue to lift into
Southcentral throughout the day. Strong winds and widespread snow
will accompany this system as it moves inland through Sunday night,
even giving Anchorage a chance for snow on Sunday afternoon. An
approaching short-wave trough is favorable for snow in Anchorage,
though strong low level southeast downslope flow may prevent any of
the snow from reaching the ground. Thus, any snow that does fall
will be light. There is also the potential for blowing snow across
the eastern Kenai Peninsula near Whittier and Portage Valley with
strong easterly winds. However, no products have been issued at this
time with some model disagreement on a potential triple point low
development over the Gulf which could impact the strength of the
winds.

&&

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

An upper level trough is currently over the mainland with
shortwave energy on the backside of it, which happens to be over
southwest Alaska. A ridge axis just upstream will glide into the
area later today, resulting in a brief dry period before the next
system approaches. By Sunday, a frontal boundary reaches the
coast and moves across the Alaska Peninsula. This front will bring
snow to the region and also usher warmer temperatures into the
region. A warm up will begin on Sunday and continue Monday.

&&

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

A mature low south of Attu Island has brought an occlusion and a
warm front into the region. The surface low was estimated at 946 mb
early this morning. As a result, there is a tight pressure gradient
force, which spans from Kamchatka to Adak, with a swath of storm
force winds stretching across the Bering. Later today, the enhanced
gradient will span northward and eastward, weakening through tonight
as it moves into the Southwest coast by Sunday morning. Expect gusty
winds and enhanced seas along with precipitation.

&&

.MARINE (Days 3 through 5 Monday through Wednesday)...

Bering Sea and Aleutian Coastal Waters: A large strong low south
of the Aleutians will have a front/trough extending through the
central Bering Sea northeast to the Kuskokwim Delta coast. North
and west of this trough a tight pressure gradient will keep gale
force wind going across the western Bering Sea through Wednesday.
This storm will usher in warmer air that will help to reduce the
amount and extent of freezing spray in the Bering Sea waters.

Gulf of Alaska: A low rapidly moves through the Gulf of Alaska
Monday that will be followed by another low that rapidly moves
across the Gulf of Alaska from west to east late Tuesday and
Wednesday. Gale force wind is likely in the Gulf of Alaska with
the first low Monday. Storm force wind is possible along the North
Gulf Coast Monday north of the low. The second low will be
crossing the southern Gulf of Alaska, thus any gales associated
with it will likely remain south of 55N.

&&

.LONG TERM FORECAST (Days 3 through 7, Monday through Friday)...
The long term forecast begins with a large north Pacific low south
of the Aleutians pushing warm air into the eastern and central Bering
Sea. We also have a moderately strong low moving across the Gulf
of Alaska into the North Gulf Coast Monday. Here the models
diverge on how strong this low will be, thus confidence on how strong
the wind will be along the North Gulf Coast is not high. This
could result in storm force wind, or minimal gale force wind and
will bear watching through the weekend. The location and intensity
of the low impacting the Aleutians is in good agreement Monday. As
we continue through the week the synoptic level pattern is in
decent agreement and the overall theme is an upper level low
anchored over the northwest Arctic coast that supports a series of
lows that transit across the Gulf of Alaska and mainland Alaska.
The models do struggle with how the low moves through the Bering Sea
Tuesday and beyond. The differences in the model solution translate
to lower confidence in any one model solution, thus we will take a
more blended approach and any changes to the forecast beyond Tuesday
will be minimal and trend to a blended solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 130 176 178.
         Heavy Freezing Spray 119 121 126 127 129 130 131 132 136-138
                              139 141
         Gales 120 121 125 129 131 132 136 138 139 150 155 165 170-175
               177 179 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...ALH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...SA