Small Craft Advisory 38, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
942 PM AKST Fri Jan 10 2020

.ANALYSIS AND UPPER LEVELS...

A deep upper level high will slowly weaken as it lifts north across
the western Bering Sea. Beneath this upper level high is a strong
surface low that sits north of Shemya. Attached to this low is a
weather front that stretches to the east, across the Pribilof
Islands, and south towards the eastern AKPEN. This front is
bringing snowfall and onshore flow to much of SW Alaska. This same
front is responsible for deteriorating snowy conditions on
Kodiak. Across central AK, clear skies and cold conditions
remain. The incredibly cold airmass across the Copper River Valley
persists, with temperatures inching into the lower negative 30's
this afternoon. The dense airmass is pushing out of channeled
areas, bringing strong winds across the Copper River Delta,
Thompson Pass Region and across a channeled corridor of the Glen
Hwy in the MatSu, not curving into Palmer as it usually does, but
remaining across northern Wasilla. Clouds are attempting to work
closer towards the southern Kenai Peninsula, but the vast majority
of the region remains clear.

&&

.MODEL DISCUSSION...

Models continue to remain in good agreement with the overall
synoptic pattern across the area over the next few days. All
guidance portrays similar outcomes with the Bering low, and first
front moving across the AKPEN and SW Alaska today. The biggest
differences start to appear towards the weekend, where the
location and movement of a triple point low, south of Kodiak, will
develop and how that corresponds to the weekend warm up and snow.

&&

.AVIATION...

PANC...VFR conditions and light winds are expected to persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

Very cold, clear conditions continue over much of Southcentral as
an Arctic air mass over western Canada maintains general northeast
flow. There are a few exceptions... a triple point low associated
with a broader low over the western Bering developed near Kodiak
Island. Snow is falling in Kodiak, and will likely continue
through late tonight. The low will drift eastward through the Gulf
Saturday, and strong offshore gap winds out of the usual bays and
passes (Resurrection Bay, Whittier, Valdez waters and the Copper
River Delta) through Saturday. Of note, since these winds have
promoted mixing, temperatures have been highly variable in the
windier places. Of note, the Wasilla airport went from -19 degrees
to 18 degrees between 11:00 am and 1:00 pm AKST... as winds
switched from the southwest to the northeast out of the Matanuska
Valley and promoted mixing. With such a steep inversion in this
Arctic air mass, it doesn't take much vertical mixing to bump
temperatures up substantially. On that note, the wind chill
advisory in Thompson Pass has been cancelled. Though winds remain
over 40 mph, temperatures have jumped up slightly. But, there
remains potential for intermittent dangerously cold wind chills,
and basic safety measures should still be followed if going
outside.

Moving forward, the next challenge will be a triple point low
expected to develop near Kodiak Island Sunday. Precipitation type
may be a challenge on Kodiak... much will depend on ambient
temperatures ahead of the warm front. Precipitation will be all
snow for points farther north, though there's uncertainty as to
how far north precipitation will propagate. Confidence is growing
that the Kenai Peninsula will see snow, but whether the Anchorage
Bowl gets anything is uncertain. Much will depend on the track of
the low.

&&

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

The next in a series of fronts continues to make inroads towards
the coast, with it expected to make landfall for most areas by
late this evening, before progressing further inland through
tomorrow. Widespread snow has accompanied this front, with even a
couple coastal areas seeing reduced visibilities. These lower
visibilities will improve over the next few hours though, as the
heavier snow band associated immediately on the cool side of the
front (over-running setup) moves inland while decreasing in
intensity, as the front slowly weakens.

Farther southwest, temperatures really signify where the front is,
as Pilot point is in the lower teens with an east wind, and Port
Heiden has punched into the warm sector, switching over to rain
while pushing 40 degrees.

Yet another front will approach the Alaska Peninsula and southwest
coast Saturday night into Sunday morning, bringing another round
of snowfall with light accumulations expected, along with a
renewed push of warmer air. This will allow for afternoon highs to
increase some more on Sunday, before some cooling commences early
next week as the flow aloft becomes more west to northwesterly,
allowing colder air to filter back in.

&&

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

A storm force low will exit the western Bering over the next 24
hours, with winds subsiding to gales. Here, seas will remain in
the 20 to 30 feet range, before subsiding on Saturday as the low
moves away from the region.

As it departs the area, a disturbance aloft dropping into the
Bering will allow frontogenesis (the development or strengthening
of a front) to take hold, with this front stretching from Saint
Matthew Island, through the Pribilof Islands, to near Dutch Harbor
by Saturday evening. Along the tail end of this front, a weak
area of low pressure will enter the region from the north Pacific,
and trek eastward along the Aleutian chain. Ahead of these
features, winds in the high-end small craft to low-end gale force
(basically winds of 30 to 35 KT) are expected, with waves of 10
to 15 feet Bering side and 15 to 20 feet Pacific side forecast.

Heading into Sunday and Monday, winds and waves will decrease for
most locations, the exception being the northern Bering, where a
long fetch length and winds at or just below gale force will allow
waves of 20 to 25 feet to persist. Precipitation wise, a general
showery type pattern will continue, with the overall trend for any
precipitation to become more brief/less intense/more isolated to
widely scattered in nature.

&&

.MARINE (Days 3 through 5)...
The western gulf will see gusty northerly flow Monday through
Wednesday of next week as the pressure gradient tights between low
pressure near the Gulf and a ridge moving to the Southwest
mainland. Small craft to gale force winds will taper down for a
short time Monday night; however, gusty winds return by late
Tuesday Morning. Across the Bering...relatively quiet weather on
Monday is followed by a gale force front moving to the western
waters Monday night. This front moves slowly across to the
central waters on Wednesday. There is still high uncertainty on
the strength of the front on Wednesday and should be monitored as
it has the potential to be stronger than currently forecast.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Dry and colder than normal conditions are on tap for much of the
southern mainland in the extended forecast Monday night through
Friday. A few snow showers will be possible across the southwest
as several weak fronts push inland. The Bering will see the most
active weather pattern as a North Pacific storm send a front to
the across the western Aleutians late Monday night. This front
moves slowly east bringing strong gusty winds and rain to the
Eastern Aleutians to Pribilof Islands. There is still some
uncertainty on the strength of this system and should be monitored
for updates. The forecast for Wednesday night through Friday will
generally be a persistent forecast with dry cold conditions over
the southern mainland and active weather over Bering and Gulf.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 121.
MARINE...Heavy Freezing Spray Warning 119 121 126 127 128 129 130
		 139 141.
		 Gale Warning 127 128 411-414 170 172 175-185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SS
SOUTHCENTRAL ALASKA...MM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...KH