Small Craft Advisory 473, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
546 AM AKDT Sat Jun 16 2018

.ANALYSIS AND UPPER LEVELS...

The well-advertised low moving north out of the Pacific has
reached southern Alaska this morning. The center of the sprawling
low remains just south of Dutch Harbor. However, nearly
unidirectional southwest flow throughout the atmosphere along with
a favorable upper level patten lead to widespread precipitation
over nearly all of southern Alaska into the evening. Currently
most of the heaviest precipitation is shifting eastward along the
north Gulf Coast and Prince William Sound. However, widespread
light rainfall continues over much of southwest Alaska ahead of
both the primary low near Dutch Harbor and a weakening trough over
northwest Alaska as part of a deformation zone.

Rainfall totals across Southcentral varied from a quarter inch in
the Anchorage Bowl, a half to three quarters inch in the Mat-Su,
three quarters to one and a half inches along the Kenai, and up to
two inches along Prince William Sound.

Winds were also a significant factor with this low. Gusts
generally were in the 30-40 mph range for most of Anchorage and
the Matanuska Valley. Palmer had a few gusts approach 50 mph. The
usual windy spots along the Anchorage Hillside had gusts of 60-70
mph, and the highest wind gust reported was a station on the
Hillside which reached 77 mph. A report of a number of downed
trees was received from Upper DeArmoun Road from the heavy winds
last evening.

&&

.MODEL DISCUSSION...

The models are in excellent agreement with the track of the
sprawling low over the Aleutians and eastern Bering as it spins
and weakens over the weekend. Disagreement between the models is
primarily focused on the next significant low to move out of the
Pacific into southern Alaska. The timing of the low is Sunday
evening through into Monday morning. The GFS is the outlier from
the other deterministic models, showing a much slower solution,
resulting in a later timing of the return of steady precipitation
to Southcentral. With the NAM/EC/GEM all in much closer agreement
and were chosen for this morning's forecast package. The high
resolution NAM was the preferred of the remaining models.

&&

.AVIATION...
PANC...SE winds associated with the Turnagain Arm Jet will
continue across Chickaloon Bay and Fire Island through the
morning. This will continue to cause LLWS to the south and west of
the airport. The Turnagain Arm wind will move back into south and
west Anchorage for the afternoon, causing gusty SE winds, which
will persist through the overnight and gradually weaken into
Sunday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Moist southerly flow aloft will continue through Sunday night with
the main upper low remain over the eastern Bering and eastern
Aleutians. Showery and fairly cloudy conditions are expected,
periodically enhanced by passing upper level short-wave troughs.
The first of these will reach the Southcentral mainland later this
morning, with another (weaker) one tonight. Fairly strong surface
pressure gradients will continue, with gusty winds through
Turnagain Arm and the Copper River valley. A more substantial
system with an associated surface low will spin up south of the
Gulf early Sunday, then race northward during the day.
Precipitation from the leading front will reach the Gulf coast
late Sunday afternoon and spread inland Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Widespread rain is falling over much southwest Alaska as the
occluded front pushes inland from Bristol Bay. This system will
slowly drift north. Expect the surface low to weaken and the front
will undergo the process of frontolysis.  The low that anchored
the occluded front will stall over the Eastern Bering and decay.
The models have that low through midweek resulting in a cooling
trend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

The North Pacific low continues its trek towards the Aleutians.
Widespread precipitation expected today for the central and
Eastern Aleutians. The surface low will cross the chain near
Unalaska today. Expect cyclonic flow over much of the Bering this
weekend. Anticipate cloudy skies and stratiform precipitation
over most of the region through the weekend. Winds and waves
reaching small craft advisory criteria will begin to subside
Saturday evening as the low dissipates.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period forecast Monday night, there will be
a very broad and impressive longwave trough stretching from the
Beaufort Sea to the eastern Bering and into the North Pacific.
Wet and cloudy weather will continue to rule the Great Land as the
blocky Eastern Pacific ridge keeps the overall synoptic pattern
blocked. By mid to late week the trough will remain in place but
will begin to weaken, resulting in stratiform rain turning more to
showers heading into Thursday and Friday. By the weekend there is
large overall model discrepancy with the ECMWF much more bullish
in moving the trough east and weak ridging building in from the
west. For now a blended ensemble approach was favored which
favors a climatological normal pattern...a trough over the
eastern Bering and weak inland ridging. Either way it does seem
that it will slowly dry out by the weekend with at least some
warming.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

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