Small Craft Advisory 82, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
358 PM AKST Fri Jan 25 2019

.ANALYSIS AND UPPER LEVELS...
A long-wave trough over the eastern Bering is weakening as the
associated upper level low continues to migrate northward towards
Norton Sound. This trough is advecting cooler air over the western
mainland and pushing it towards Southcentral. Ahead of the
trough, a ridge is building over the central and eastern Gulf. The
jet stream is vertically oriented over the Gulf, coupled with the
western edge of the upper level ridge. The winds in the jet
streak are approaching 150 kts at 300 mb. This jet streak can be
observed in IR satellite imagery as a swath of cloud cover
extending from the Pacific Ocean through the Gulf into Southeast
Alaska. Another section of the jet, albeit weaker, is over the
central Aleutians. This portion of the jet coincides with a
vertically stacked, intensifying North Pacific low that is
advancing towards the western Aleutians.

At the surface, an occluding front continues to move inland ahead
of the upper level trough over the eastern Bering. This front,
and associated cooler air, has created precipitation and
southerly flow throughout southern Alaska. The influx of cooler
air will cause temperatures to drop just below freezing through
Southcentral tonight. The strong winds experienced through the
Turnagain Arm, Cook Inlet and Shelikof Straight continue to be
blow as that front moves through the area. A second front is
moving over the western and central Aleutians ahead of the
incoming low in the North Pacific, which is ramping up winds in
the area.

&&

.MODEL DISCUSSION...
Models overall are in relatively good agreement through Sunday
afternoon. Models differ some on placement of the low centers
within the complex moving into the Aleutians in the low complex
approaching the Aleutians/Bering Sea tonight and Saturday.
However, they all have a similar handling the the frontal trough
and pressure gradients and resultant wind fields.

&&

.AVIATION...
PANC...VFR conditions are expected. Their could be a brief period
of MVFR showers this afternoon, but the probability is low. Gusty
southerly winds across the airport complex will weaken later this
evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Breezy southerly winds will continue to diminish through the
evening as today's frontal system lifts further away to the north.
Cold advection from an upper level trough pushing in from the
west will drop temperatures steadily overnight with snow levels
dropping back down to sea level. In most areas, however,
precipitation has already tapered off to scattered or isolated
showers with exceptions being the northern Gulf coast, Talkeetna,
and northern Chugach mountains and northern Susitna where showers
are more abundant. Snow showers in these areas are expected to
continue overnight with the support of the cold, unstable air mass
pushing over the area and then taper off through Saturday
morning. An inch or two of snow is possible in the Talkeetna area
with 3 to 6 inches further north and in the Hatcher Pass
vicinity.

Upper level ridging will build back over Southcentral Alaska
Saturday afternoon through Saturday night bringing a period of
drier conditions. The upper ridge will amplify and shift east on
Sunday, opening the Gulf back up to southerly flow aloft with the
next frontal system moving into the southern Gulf Sunday
afternoon.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The remnants of a system have pushed across Southwest today. The
latest METARs and other observations across the region depict a
mosaic of rain and snow. The radars at King Salmon/PAKC and
Bethel/PABC still have pockets of light precipitation on them as
of 3:43 PM or 0043Z. Significant accumulations are not expected
tonight but there is still a little juice left in the air. Expect
a short break between systems, then a Bering storm will usher
another batch of moisture into the region. Looking at thickness
values and model soundings, again there is a chance for a wintry
mix or rain/snow. Between the complex terrain and the complex
thermal profiles, it will be really tricky pinpointing the exact
p-type for each location, but very confident on the track of the
storm into Southwest Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A progressive and unsettled pattern is on tap this forecast
period. There is a decaying surface low near Norton Sound, a
surface low southwest of Adak and a secondary surface low near
Attu Island. There is a mature frontal boundary south of the
Aleutians and looking at model data and the latest Himawari
satellite image the associated cold front extends all the way
south to the Mariana Islands. Tonight expect the surface low
associated with this boundary to jump the chain and deepen a
little. The low near Attu will become absorbed into the longwave
pattern. A secondary wave will develop along the baroclinic zone
south of the Aleutians this weekend. Meanwhile, an entirely new
low will undergo rapid cyclogenesis east of Japan and begin to
track towards the Western Aleutians. But the brunt of this storm
is expected just beyond this forecast period.

&&

.MARINE (Days 3 through 5)...
The models have come into good agreement with the low near the
western Aleutians Sunday night into Monday resulting in high
confidence in the area seeing storm force winds. Confidence lowers
on Tuesday as the models diverge with the track of the low, but
there is agreement that the wind speed will weaken. The models are
also struggling out east in the Gulf with a low tracking into the
area from the south on Monday. Some of the guidance is looking at
gale force winds through much of the marine areas in and around
the Gulf on Monday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast is plagued by model uncertainty resulting
in a forecast leaning towards the ensemble means. The area of
highest confidence is with a storm force low approaching the
western Aleutians Sunday night into Monday. There is also decent
confidence in ridging over the panhandle holding over the area
into mid week with multiple lows tracking through the area to the
west of the ridging. The models are struggling with the timing
and intensity of these lows resulting in the ensembles being
preferred. This setup will likely result in more above average
temperatures for most locations in the southern mainland.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 155 172.
 Gale Warning 150 160 165 170 171 174 176 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RA/RC
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...DK