Small Craft Advisory 186, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
418 AM AKST Thu Mar 1 2018

.ANALYSIS AND UPPER LEVELS...
The upper level pattern remains highly amplified this morning,
with a full latitude ridge extending over the west coast of Alaska
bounded by longwave troughs over the Bering Sea and western
Canada. This is keeping broad northerly flow focused over
Southcentral Alaska, with strong outflow winds being aided by a
140 kt jet streak diving down the back side of the Canadian
trough. Much calmer conditions prevail across the southwest
mainland beneath the ridge. Meanwhile, a strong front is
continuing its steady eastward progression across the Bering Sea,
bringing southerly gales and occasionally heavy rain to the
Pribilofs and Eastern Aleutians overnight.

&&

.MODEL DISCUSSION...
Guidance remains in good synoptic agreement into the weekend as
the ridge slides eastward across the mainland, bringing a gradual
end to the outflow wind regime over the course of the next 24
hours and keeping a progressive pattern going beyond the short
term. The most notable model difference occurs near the end of the
short term as the next trough moves across the state and brings
another chance for snow to Southcentral on Saturday. The 00Z NAM
is notably drier than the other guidance, and was treated as the
outlier for the morning package. Otherwise, continued to utilize
Hi-Res NAM guidance to handle the final few periods of the outflow
wind event.

&&

.AVIATION...
PANC...VFR conditions and northerly winds will prevail through the
TAF period. Winds should become less gusty through this morning as
the best upper level support moves off to the east.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Strong gap winds along the North Gulf Coast and Prince William
Sound will continue to gradually diminish today as the upper level
jet exits to the southeast and an upper level ridge approaches
from the west. Winds will drop off more significantly tonight as
the ridge moves overhead of Southcentral. Winds blowing through
the Matanuska Valley will follow a similar trend.

Otherwise, expect another sunny day across the region with
temperatures below average for this time of year. Cirrus clouds
will move in tonight, but it doesn't look like enough clouds to
limit radiational cooling very much, so it will be another cold
night. A weak front will stall over Southwest Alaska on Friday
while a low moves up from the North Pacific toward the Alaska
Peninsula. Kodiak Island will remain on the northern periphery
of the low, so the best chance for precipitation will be the
south end of the island.

It looks favorable for a light snow event for Southcentral Friday
night into Saturday as an upper level short-wave marches eastward.
Vertical motion will come mostly from the upper levels, with very
little going on in the low levels. With a neutrally tilted trough
and an inland track of the strongest part of the wave, snow will
be most likely from Anchorage and the Mat-Su eastward to the
Copper River Basin. Unlike recent storms, best estimate for
accumulation at this point is an inch or two, with perhaps a
bit more on the west side of the Talkeetna Mountains. While some
snow may move in as early as Friday night, the most likely period
of snow will be Saturday as the trough cross through Southcentral.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...
Ridging over Southwest Alaska will continue to track east today
and as the ridge axis moves east of the area late this morning,
warm southerly flow will be ushered in over the area helping to
raise temps. This evening the front over the Bering will push in
over southwest Alaska bringing snow to the Kuskokwim Delta. As it
pushes further inland, part of the front will stall in a corridor
from the Bristol Bay area through the Lower Kuskokwim Valley that
will produce showers through Friday and into early Saturday
morning. Then weak ridging will move in ahead of another front
that will make it to the Kuskokwim Delta Saturday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...
The front that extends across the Pribilof Islands and eastern
Aleutians is tracking east and will make it over the mainland this
evening. Cold westerly flow with embedded snow showers will then
dominate the area until a new system moves in over the western
Aleutians Friday afternoon. This front will make it to the central
Aleutians Saturday morning and the eastern Bering Saturday evening.
It is also pulling up enough warm air to bring rain or a mix of
rain and snow to the islands as it passes.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The operational run of the GFS continues to display good run to
run continuity. At the onset of the forecast period, the GFS
ensemble members are tightly clustered with the low near
Kamchatka, the high south of the Central Aleutians and a low south
of Prince William Sound. As the forecast period unfolds, the
ensemble members remain grouped for the dome of high pressure in
the North Pacific, but the consensus quickly unravels in the
Bering. Very confident in the progressive nature of the pattern.
The GFS continues to depict three distinct frontal passages
across the Bering this forecast period with the remnants of these
systems moving into Southwest Alaska. East Domain (Kodiak,
Anchorage and Valdez) sensible weather highlights include a batch
of wintry precipitation for Kodiak and the southern Kenai
Peninsula Saturday March 3rd that will move across the Gulf of
Alaska later Saturday and Sunday. Monday, a new batch of wintry
weather is anticipated to impact Kodiak with moisture working its
way up Cook Inlet later Monday impacting the Anchorage Metro Area
Tuesday and Wednesday. The third batch of wintry weather is
anticipated for Southcentral late Thursday. In a nutshell, the
Anchorage Bowl and the Mat-Su Valleys can expect more snow! Stay
tuned for more details.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 127 128 155 165 170 172 178 180 181 414.
 Heavy Freezing Spray: 160.

&&

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...PJS