Small Craft Advisory 857, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
409 AM AKDT Fri Nov 2 2018

.ANALYSIS AND UPPER LEVELS...

A fairly amplified omega block extended from the Gulf through
central Alaska this morning, with just a few high clouds passing
by as subsidence under this ridge is really helping to suppress
moisture condensation. The exception to this is along the eastern
edge of the ridge, where low stratus is once again developing
across portions of the Copper River Valley.

Farther west, a 160+ knot upper-level jet is helping to deepen a
surface low southwest of Dutch Harbor, as left exit dynamics
provide plenty of support aloft to foster this. Currently the low
has strengthened to 957 mb, with storm force winds and heavy
rainfall accompanying it near the low pressure center itself.

&&

.MODEL DISCUSSION...

This mornings numerical runs are in excellent agreement at the
surface and aloft, with virtually all of the models on top of one
another in their numerical fields. This leads to a high confidence
forecast in the short term, with just minor temporal differences
as the system progresses into the weekend.

&&

.AVIATION...
PANC...Locally dense fog this morning is expected to burn off this
afternoon. With a front moving in this afternoon, cloud cover is
expected to keep fog from redeveloping again overnight. Winds will
be below 10 knots and VFR for the remainder of the TAF period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure over the area will slowly slide north through
Saturday afternoon as a low currently over the eastern Aleutians
moves east into the western Gulf. An occluded front associated
with this low will bring rain and gale force winds into Kodiak
this morning, and then to the north Gulf Coast by this evening.
The front will then stall and weaken tonight into Saturday, and
then dissipate Saturday night. Most of the precipitation with this
system will fall along the southern and eastern Kenai Peninsula,
with very little or none expected further inland. The high
pressure to the north will begin to build back southward Saturday
night as the upper low moves eastward across the Gulf.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today through
Saturday Night)...

A very quiet morning weather-wise across Southwest Alaska will
begin to get a bit more active through the day today. Cold high
pressure over interior Alaska contrasting with the strong low and
front heading towards the area will make the upcoming system
primarily a wind-maker over the next 24 to 36 hours. Along with
the gusty winds will be rain moving in this afternoon along the
coast across portions of Bristol Bay. The strong easterly winds
will induce downsloping to areas to the lee of the Alaska Range
and Kuskokwim Mountains, so the main areas expected to get
precipitation will be through Dillingham and northward along the
east side of the Kuskokwim Mountains. For the most part the valley
rain and mountain snow will be light. Warmer air associated with
the front will be the reason any precipitation later today should
fall as rain, while higher elevations of the Kuskokwim Mountains
along with locations further inland may see a bit of light, wind-
driven snow. No major accumulations are expected as the front
falls apart and weakens quickly as it presses northward into
Southwest Alaska. The winds are likely to persist into the day
Saturday, though diminishing with time as the parent low itself
weakens and tracks to the south of the Alaska Peninsula on
Saturday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
through Saturday Night)...

A strong low currently centered southwest of Unalaska Island
remains the primary weather maker across the area this morning.
Localized areas of storm force winds with widespread gales are
ongoing across the Aleutians and the waters on either side of the
Alaska Peninsula. Since the low has somewhat warmer air associated
with it, all of the associated precipitation at lower elevations
is falling as rain. Wind is the primary impacting weather
associated with the low. The strongest winds are associated with
the occluded front tracking east away from the center of the low
through the Alaska Peninsula. The front itself has begun
weakening, which should gradually diminish the threat of storm
force winds today, however, gales will persist until the front
falls apart this evening. The low center has largely stalled out,
but will begin a slow eastward movement by tonight, tracking along
the Pacific side of the Alaska Peninsula on Saturday. Meanwhile
the low is likely near its peak intensity now and will weaken
steadily through the day Saturday. Weak surface ridging will
follow behind the low Saturday and Saturday night across the
central and eastern Bering, while a cold front associated with a
Kamchatka low enters the western Bering late Saturday night. This
front will be the main weather maker across the Bering through
Monday.

&&

.LONG TERM FORECAST (Days 3 through 7/Sunday through Thursday)...

The extended forecast still looks to have high amplitude ridging
over mainland Alaska, with a low in the Bering Sea this weekend
into early next week. One difference from yesterday is that the
GFS is no longer attempting to push the low in the Bering through
the high pressure over mainland Alaska. It has come into alignment
with the other major models, so confidence is now high the solution
long term will be calm weather for southcentral Alaska under high
pressure, with active weather in the Aleutians due to low pressure
there. Gale force winds will be likely in the Bering with this low.

Toward the end of the forecast period (Wednesday through Thursday),
there is another low that tracks through the Gulf of Alaska
underneath the high pressure system over mainland AK. There is
some uncertainty with the track of this low, with some models
favoring a southerly track in open water, while others keep it
closer to the coast. The more coastal track would bring some
active weather along the coast of Southcentral AK. Right now, due
to the overall pattern, the southerly track looks more likely.
However, this does bear watching next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 119 120 130 131 132 136 137 138 139 155 160 165 170
174 179 180 351 352 414 Storm 150

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...BJB