Small Craft Advisory 578, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKDT Mon Aug 7 2017

.ANALYSIS AND UPPER LEVELS...
The synoptic pattern features a broad upper level low with the
center of circulation south of Cold Bay. With robust ridging to
the east...this vortex has been quasi-stationary but has managed
to eject multiple short waves into the AK Peninsula and SW
Alaska...resulting in precipitation and instability. On the back
side of the low...an enhanced pressure gradient has developed
producing gusty winds over the western Aleutians.

&&

.MODEL DISCUSSION...
The models continue to be in good agreement through the short term
from SE AK to the Central Aleutians, and there has been excellent
run to run consistency. The models are out of sync with the next
Bering low to impact the western Aleutians. The ECMWF is a little
more bullish with its trajectory bringing the storm in 12+hrs
ahead of the GFS and the NAM. Hedged towards a more subtle
progression of this low.

&&

.AVIATION...
PANC...VFR conditions expected for the ensuing 36 hr period.
Turnagain Arm winds expected to materialize later in the day.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
While today will still be the day that Southcentral Alaska starts
to see the pattern shift to a cooler and more moist one, the
transition will be slightly slower allowing another overall nice
day today. This will be especially true for the farther inland
areas of the region. This is due to the ridge being a little
slower in breaking down, but the ridge is giving way and tonight
into tomorrow will see a marked change.
The big forecast question for Tuesday and Wednesday is how far
inland the rain will make it and how much will rain will be
dissipated by the downsloping off the Kenai and Chugach Mountains.
At this time it looks more likely for the rain to make a more
significant push into Anchorage and the Mat-Su on Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A period of showery southeasterly flow is setting up across the
mainland. Another round of afternoon showers with embedded
thunderstorms are expected for the Kuskokwim Delta, however,
lightning activity as we saw last night is not expected again.
Showers will increase in coverage this afternoon and evening for
the Bristol Bay area as an upper level disturbance rotates in from
the Pacific. A brief break is in store, but still with some spotty
shower activity on Tuesday, but the next disturbance comes in
quickly late Tuesday in to Wednesday.

The front/disturbance will be stronger than previous, accompanied
by gusty southeasterly winds, which will take some bite out of the
precipitation along the Aleutian Range. Once the disturbance and
front pass, a showery and cloudy southeasterly flow will remain
with near normal temperatures.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A front entering the western Bering divides two air masses; fog
and low stratus to the west, and the showery upper low to the
east. The front will stall in place tonight as the connected low
pressure system drops in behind it. A stronger front and
disturbance enter the eastern Bering Sea late Tuesday into
Wednesday bringing steadier rain and stronger winds.

&&

.LONG TERM FORECAST (Days 4 through 7)...
A progressive wet weather pattern remains through the long range
forecast. On Wednesday night, a front will be pushing across the
southern mainland with ongoing precipitation into Thursday as
additional upper level waves pinwheel around a low tracking near
the Alaska Peninsula to the southeastern gulf. For the end of the
week, the pattern is expected to stay active as energy dives south
from the the arctic and another wave moves toward the western
Bering. The models all shifted out of agreement on the long range
solutions today, so kept the inherited forecast intact as the
previous tracks of the synoptic systems looked more reasonable.
The most challenging forecast problem for both the ECMWF and GFS
is that there are multiple strong waves moving toward the mainland
into next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...KH