Small Craft Advisory 131, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 PM AKST Fri Feb 9 2018

.ANALYSIS AND UPPER LEVELS...
An active pattern continues across the Bering with a broad
long-wave trough spread over the Bering Sea and north Pacific.
The next closed low within the flow is on a northward track just
south of Dutch Harbor today. Moisture-rich southerly flow
streaming from the north Pacific spans across Kodiak Island and
into Southwest Alaska today, with rain and snow being observed
across the majority of the area. Otherwise, the synoptic pattern
remains highly amplified with a ridge centered across the eastern
portion of the mainland, with more dry and clear conditions being
observed over Southcentral.

&&

.MODEL DISCUSSION...
Models remain in good agreement with the synoptic pattern through
Sunday, then begin to struggle with the details regarding the next
system tracking across the AK Pen overnight Sunday into Monday.
There are some important differences between the models in the
evolution and track of this system as it progresses northeastward
through the Gulf Sunday night into Monday. During this time frame,
models are in agreement with a warmer airmass pushing over the
Southern Mainland and briefly moderating the temperatures over the
area. However, confidence remains low as the models continue to
struggle with the timing and precipitation type details as this
system tracks over the area.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

Upper-level ridging which has been the dominant feature in our
weather the past couple of nights, aiding in fog development,
will continue to slide of to the east overnight before refocusing
its center across the Northeast Pacific on Sunday. With increasing
winds/mixing extending from the Kenai Peninsula northward through
the Anchorage Bowl into the Matanuska valley, fog concerns here
will be minimal with perhaps some localized development in the
tighter valleys where winds may be more sheltered. Still, temporal
and spatial coverage was low enough to preclude it being in the
zone forecasts.

Further east across the Copper River Valley, the ridge will be
directly overhead tonight and area web cams suggest some stratus
off in the distance from Gulkana to McCarthy. Given this has been
prevalent the past couple of days and the ridge overhead, we opted
to keep the previously mentioned patchy fog in the forecast
through Saturday morning, while removing it for the afternoon
hours as southerly winds develop behind the departing ridge.

The next item of interest will be a weakening will be a fairly
potent front currently affecting the AKpen through southwest
Alaska. This front has brought near hurricane force gusts to some
parts of that region. However, the front will be bumping up
against the departing ridge with 500 mb plots showing the
vorticity associated with it elongating while as frontolysis
commences. Still, it'll have enough forcing with it for high end
gales/low end storm force winds to persist through tonight from
the Barren Islands through the Kodiak/Western Gulf area.

Although the actual surface front will approach the Kenai
Peninsula in a weakening state, disturbances crossing the front
aloft will be instrumental in allowing precipitation chances to
spread through the region into the Anchorage Bowl/Matanuska
Valley and along the Gulf coast, decreasing in coverage towards
the Copper River Valley. As for precipitation type, most
locations will likely see snowfall across the interior with some
light accumulations a good bet. The exception to this will be the
lower Cook Inlet, and near the coastal locations where enough
maritime warming should allow for more of a mix to occur. Another
storm system also looks to impact the region just beyond the short
term period.

&&

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

The weather front currently bringing strong winds and widespread
precip to most of the region will slowly lift northward tonight
through Saturday. Hazardous blowing snow conditions are occurring
along the Bering coast north of Toksook Bay, and will continue
through the evening. Temperatures have warmed into the 30s across
the Bristol Bay zone and parts of the Kuskokwim Delta, and as
winds slowly shift to more southerly over the weekend these mild
temperatures will continue and will actually spread even further
inland. Meanwhile, the steady precipitation will taper off from
south to north, but shower conditions in the onshore flow will
continue through Sunday afternoon.

&&

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

With the weather front now pushing away from the area and into the
Southwest Mainland, the next storm to impact the region is already
beginning to move northward out of the Pacific toward the central
Aleutians. This storm will struggle to produce more than gale-
force winds, and even these will not be terribly widespread. In
general, temperatures will be warm enough that even on the
west/cold side of the storm (near the Central ALeutians)
temperatures should stay near or above freezing, so even where
snow will be the dominant precipitation type no significant
accumulations are expected. There will be a break between storms
Saturday Night and Sunday, another storm will follow the same
track and impact the Aleutians by Monday morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A change to a warmer pattern remains in store for the beginning
of next week. On Monday, a low pressure system approaches the AK
Pen from the North Pacific and then moves into the eastern Bering
Sea. This system is accompanied by a lot of warm air, which makes
precipitation type a challenge for Monday's forecast. Models have
been somewhat inconsistent with the track of this low as well,
finally coming into some agreement with this morning's 18Z run.
Current forecast brings keeps a more southerly flow aloft, which
indicates a greater chance for precip reaching the lee side of the
mountains. This will also prevent a true snow-eater Chinook in
Southcentral, but some liquid precipitation is expected with
temperatures rising into the 30s at the surface.

On Tuesday and Wednesday, a short wave ridge will move through the
region, temporarily clearing skies first in the eastern Bering,
then over the mainland. This ridge is followed by a series of low
pressure systems that move into the central and western Bering.
Models forecasts have been very inconsistent on these next
systems, so there is little confidence in the forecast past
Wednesday. Still, the pattern looks to remain active through the
end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 155.
MARINE...Storm 130.
         Gale 120 131 132 136 137 138 139 150 155 160 180.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AMD
LONG TERM...LF