Gale Warning 127, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKST Wed Feb 27 2019

.ANALYSIS AND UPPER LEVELS...
The ridge over mainland Alaska has shifted eastward to over the
Alcan border this afternoon, resulting in dry conditions across
Southcentral today. Stratus has developed along Cook Inlet and the
Kenai Peninsula earlier today and will be the deciding factor if
Anchorage and surrounding areas see blue skies again today. This
blocking high ridge pattern is less amplified than it was over
the past few days and is starting to weaken, due to the remnants
from yesterday's Bering low shearing along the ridge access. A few
snow showers have been observed along the Kuskokwim coast
associated with this low that has now moved into the northern
Bering. Out west, a low situated over Adak and the central
Aleutians has brought gale force winds and mainly rain showers, as
this long fetch of moisture and southerly winds move up from the
North Pacific.

&&

.MODEL DISCUSSION...
Models have been in good consensus over the past few model runs,
thus leading to good confidence in the synoptic pattern through
the forecast package. The GFS/NAM continue to be in agreement with
intensity and placement of the strong low that moves north across
the Bering Sea through Friday. Models over the Gulf agree that
this ridge pattern will break down Friday morning, but models
differ in whether high pressure will remain over the Gulf, or if
a trough of low pressure and showers along the coast (NAM
solution), will be the next pattern. More details are discussed
in the Southcentral section.

&&

.AVIATION...
PANC...Once again, patchy fog will be a threat at the terminal.
Going with pure persistence, the general thinking is that fog will
develop toward morning, but will be more patchy instead of
widespread. Confidence is not high however since the pattern is
slightly different than previous days.

&&

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

An upper-level shortwave is shearing apart as it moves east of the
Susitna Valley. Behind this system, a weak northerly lower and
mid-level flow will develop, aiding in the erosion the low
stratus deck situated over Cook Inlet. Areas of fog are possible
again overnight across northern Portions of Cook Inlet and the
Anchorage Bowl as the northerly flow weakens and radiational
cooling under mostly clear skies reestablishes strong surface
inversions. The pattern then begins to slowly change on Thursday
as the ridge weakens and a shortwave advancing from the west acts
to split the upper-level ridge, with half the ridge moving north
towards northern Alaska and the other half drifting south through
the Gulf. The split will leave the Southcentral mainland in a This
will leave the Southcentral mainland in a "col", with high
pressure to the north and south and troughs situated to the east
and west. Between these features, conditions to will remain for
the most part clear and dry, with only some patchy overnight/early
morning fog along Cook Inlet and some lingering outflow winds
near the Copper River Delta. An easterly shortwave trough will
dive south through the Copper River Basin on Friday, displacing
the split ridges to the north and south, respectively. From this
shortwave, a surface trough will develop along the northern Gulf
coast, bringing clouds and a chance for scattered rain/snow
showers from the Copper River Delta west to Prince William Sound
Friday evening through Saturday. Farther west, a shortwave
advancing east from the AKPEN will bring clouds and precipitation
to Kodiak Island and the southern half of Cook inlet by the
weekend.

&&

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

Overall, a similar pattern is in store with southerly flow and
relatively warmer temperatures. The remnants of a frontal system
are drifting eastward over Southwest and as the leading front
associated with a storm force Bering low continues to track to the
northeast, and it will soon be hard to tell the difference
between the stalling front and the arriving front. Southerly flow
along the AKPEN will allow for some gusty conditions through the
usual gaps and passes overnight tonight before diminishing
Thursday afternoon. Temperatures across the Kuskokwim Delta will
initially be cold enough for snow, however as warm air arrives by
Thursday afternoon, a change to a rain/snow mix or even all rain
is possible. Meanwhile, temperatures along the AKPEN and Bristol
Bay area will be warm enough for precipitation to fall as rain. As
the associated Bering low lifts northward out of the Bering by
Thursday afternoon, gusty southerly winds will persist along the
Southwest coast through Thursday evening before diminishing early
Friday morning. Generally fair conditions are in store for Friday,
with any remaining precipitation falling as a rain/snow mix.

&&

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

A North Pacific low is moving over the central Aleutians. Its
leading front is bringing in a large area of warm southerly flow
over the central and eastern Aleutians. Precipitation associated
with this front will fall as rain along the eastern Aleutians as
temperatures will initially be warm. As the low moves further
north into the Bering by Thursday morning, cold air on the back
side of the low will allow for snow showers across the western and
central Bering through Thursday evening. More notably, a large
area of gales with embedded storm force winds will track northward
through Thursday with southerly gales and storm force winds over
the eastern Bering. This swath of storm force winds will cross
over the Pribilof Islands Thursday morning before lifting
northward out of the Bering by Thursday afternoon. Much quieter
conditions are in store for Friday before the next Bering low
approaches the western Aleutians for the weekend.

&&

.MARINE (Days 3 through 5)...

Confidence is high for upper end southerly gales and storm force
gusts to develop over the western Aleutians overnight Friday into
Saturday along a cold front associated with a strong low moving
into the Bering. The core of the low center will track just west
of Attu Saturday night and thus strong winds and high seas will
persist there through much of Sunday. Otherwise, the
aforementioned front will continue to track west to east over the
weekend. Winds will diminish and seas subside as the front
approaches the strong blocking ridge that has been in place over
the mainland for several days. Sustained gales appear less likely
east of Cold Bay. Sub gales and lower seas are expected Monday
across the Bering in weaker westerly flow behind the departing
low.

Sub gales and generally calm seas continue over the Gulf through
Monday under a strong ridge.

&&

.LONG TERM FORECAST (Days 3 through 7)...

A cold front associated with a low over the western Bering is
expected to bring moderate precipitation to the Aleutians this
weekend. As there is southerly flow ahead of the front, this will
be in the form of rain or a rain/snow mix for many areas.
Agreement slightly deteriorates after Sunday, with the GFS
solution indicating a weaker low departing much quicker just to
the west of Nunivak Island by Monday afternoon whereas the ECMWF
and Canadian models show a stronger low centered west of St. Paul.
The latter solutions would favor longer duration precipitation
for the eastern Aleutians and the southwest mainland, where there
could be the chance of accumulating snowfall. In general all
models show a weak ridge building in behind the aforementioned
low on Tuesday. Confidence is moderate for a strong, broad low to
move roughly over Attu Wednesday. The associated front will bring
strong southerly flow and moderate rain and quickly (with strong
westerly winds behind it) track west to east across the Aleutians.

Fair skies expected over Southcentral Saturday under a ridge. A
weak shortwave trough will move over the region Sunday. Exact
timing is still uncertain (ECMWF slightly faster) however overcast
skies are likely and brief light snow cannot be ruled out. A ridge
will build in behind the front on Monday. ECMWF is more amplified
given the stronger low digging behind it as mentioned above. This
would lead to clearer skies as opposed to the less-amplified GFS
solution. The strong blocking ridge that has persisted over
Southcentral the past week will finally fully depart the region
Tuesday as the GFS and Canadian models indicate a possible snow-
producing trough moving over the region. While the ECMWF is not as
aggressive, it appears a more active pattern is likely mid to
late next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 165 171 175 177 180 181.
		 Storm 170 172 173 174 176 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AH
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...AP/KVP