Small Craft Advisory 537, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKDT Tue Jul 10 2018

.ANALYSIS AND UPPER LEVELS...

A broad upper level trough is still in place over much of the
state this morning. The slow-moving 991 mb surface low has inched
inland over Kipnuk and radar indicates rain is still falling over
much of southwest Alaska and the AKPEN. The effects of this low
are also reaching Southcentral as the leading edge of the front
has remained nearly stationary overnight in the central Gulf. This
southerly flow continues to pump moisture into the southern
Mainland this morning with rainy conditions observed along the
entire Gulf coast and into the Mat-Su Valleys (though very little
rain has been observed in the Anchorage area due to downsloping).
Gusty southeast winds are still occurring along the coastal areas
of Prince William Sound and in localized areas across the
Matanuska Valley. Behind the low, drier northwest flow has
increased, allowing for some areas of dissipating cloud cover in
the southern Bering.

&&

.MODEL DISCUSSION...

Models remain in good agreement with the timing and strength of
the low moving inland over the southwestern part of the state.
Uncertainty arises mid-week as a Kamchatka low enters the western
Bering and a North Pacific low approaches the Aleutians from the
south. At this time, the GFS has a more easterly position for
both of these lows, while the NAM hangs back to the west. By the
end of the week, models disagree on the timing and location of the
convergence of these lows over the southern Bering. However, one
noticeably consistent feature is a ridge ahead of these lows (to
the east) that lifts over Southcentral toward the end of the week.

&&

.AVIATION...

With down-inlet flow pulling the Turnagain Arm winds further away
from PANC and the overall southeasterly pressure gradient
weakening, winds at PANC have switched to light northeasterly
early this morning and precipitation is having an easier time
holding together as it spreads over the terminal. Southeasterly
winds will return around midday and then gain more of a southerly
component as the afternoon and evening progress. In addition to
this shift in wind direction, an increase in instability will aid
in bring more numerous showers training over the Anchorage area
with heavier showers having the possibility to briefly lower
conditions to MVFR at times.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper low centered over the Kuskokwim Delta will be nearly
stationary today, drifting only very slowly eastward. A fairly
strong trough associated with this low will push through
Southcentral today, brining rain and showers to much of the area.
This trough will then slide east of the area this evening. Tonight
the main upper low will accelerate eastward, becoming an open
trough by Wednesday morning as it pushes through Southcentral.
This will bring more showers over the area. The trough will then
slide east of the area Wednesday night, and a ridge will begin to
move in behind it. Showers will taper off and/or end as a drying
trend begins.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The weakening low over the Kuskokwim Delta will continue to
support cool and cloudy conditions characterized by widespread
showers across the southwest mainland through tonight as it
tracks eastward towards the Alaska/Aleutian Ranges. Showers will
diminish in coverage from west to east on Wednesday as the low
departs to the east, with partial clearing allowing afternoon high
temperatures to creep back up towards seasonal normal values. The
respite from the cool and wet pattern will continue into Thursday
as weak transient ridging moves through the region in advance of
the next system developing in the Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Weak cold advection on the back side of the low sitting over
Southwest AK will continue to support scattered showers across the
eastern half of the Bering today before tapering off by late
evening as the system moves off to the east. Attention then turns
to a pair of systems poised to enter the western Bering as another
low drops out of eastern Russia this evening and then a North
Pacific disturbance move over the Central Aleutians late
Wednesday. These two systems will phase with one another and bring
another round of rainy and windy conditions to the central Bering
before moving inland late Thursday.

&&

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

The long term forecast periods begins Thursday evening with a
departing upper level trough moving into Canada and a deepening
low over the Bering Sea. The models have dramatically slowed down
the eastward progression of the Bering low, so it now seems that
Thursday looks to be a nice "break" in the weather across Southern
Alaska as shortwave ridging builds inland. The Bering warm front
will then move into Southwest on Thursday night and early Friday
then make quick eastward progress into Southcentral by Saturday.
The low will merge with a series of shortwave troughs moving down
from the Arctic region, so it does seem that the low will linger
over Southern Alaska through at least Monday before moving east
and weakening. Models continue to strongly hint at some form of
Bering ridging building in early next week which means warming and
inland drying seem increasingly likely.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 145
MARINE...None

&&

SYNOPSIS AND MODEL DISCUSSION...KO
AVIATION...JR
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...Ahsenmacher

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