Gale Warning 380, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Fri Aug 11 2017

.ANALYSIS AND UPPER LEVELS...
The pattern is starting to get a whole lot more interesting.
First, the synoptic set-up continues to be dominated by two closed
upper level lows. The first is centered over Bristol Bay, while
the second is parked over the high Arctic. The first low will
migrate into the northern Gulf of AK through the day. As it does
so, it will reinforce the widespread rain (and embedded moderate
showers) along the Gulf Coast up through Prince William Sound.
Some of this rain is making its way over the Chugach and Kenai
mountains and we should only continue to see the radar become more
active through the morning. While there are several weak waves
rotating around this low, the primary front is still centered over
the Gulf of AK and won't bring the heaviest precipitation to
Southern AK until later tonight.

Low #2 is clearly visible on satellite centered way up at 80N.
However, the piece of energy it is ejecting southward is over the
Bering Strait region. It is moving quickly along 105 kt polar jet
and has an associated -26C cold pocket at 500mb. With that much
instability, we have seen a rather impressive lightning show
unfold overnight from NE Russia down through the northern portion
of the Bering. This low will set the tone for a cooler and wetter
end of the week and weekend for much of Southern AK, especially
over the southwest.

&&

.MODEL DISCUSSION...
Models continue to handle the overall synoptic pattern fairly
well, but are not in agreement on some of the smaller-scale items.
This is lending to overall low-moderate forecast confidence,
especially regarding exact timing and intensity of precipitation.
The American models were preferred in handling the Bristol Bay low
as it "reforms" in the Gulf and in the stronger trough diving down
from the Bering Strait. The EC has been struggling with both of
these features the past 4 runs or so. Some of the key areas of
uncertainty are with precipitation around Cook Inlet today,
thunderstorms holding together over the Bering, and exactly cold
the airmass will be Sat night-Sun as it crosses the AK Range.

&&

.AVIATION...
PANC...Light rain this morning will yield to some heavier rain
this evening, which would likely produce MVFR ceilings for a short
period. Winds will remain light.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A upper low complex near the AK Pen continues broad southerly flow
aloft over much of Southcentral. A large plume of moist air
associated with a frontal boundary and north advancing low over
the Gulf will bring moderate to locally heavy rains along the
coast today. Rain, though not as heavy, will spread inland west
and north of the Chugach this afternoon and evening. Rain will
likely continue along the coastal locations through tonight, but
should diminish inland. Winds will start to ramp up today across
the North Gulf marine areas as the surface low intensifies and
heads north.

On Saturday, the upper low currently over the AK Pen moves into
the Gulf then is pushed north as a vigorous cold upper trough digs
across Bristol bay and the western Gulf. This system will likely
bring cooler air and more unstable air across much of the Gulf and
Southcentral. The convective nature of this system will bring an
enhancement of the rain/showers Saturday afternoon/night.
Current thinking is that snow levels should remain above
4500 ft Saturday night/Sunday morning. Low level cold advection
with and instability will also give rise to brisk and gusty winds
across the western Gulf Saturday/Saturday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Energy will get kicked out of the vortex over the AK Pen resulting
in another round of unsettled weather. Generally expecting showers
and isolated thunderstorms. As time elapses...expecting a strong
cold front to push across the Bering Sea and into the Mainland.
Temperatures will plummet with this storm and this will bring a
taste of fall to the region. Sensible weather-wise...expect gusty
winds...another round of rain, and snow at higher elevations.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A strong low will move into the domain later today. Expecting
another round of precipitation. Gale force winds are expected
mainly along the coastal waters of the Kuskokwim Delta late Friday
night through early Sunday morning. All the while...the eastern
edge of a high pressure system over Russia will influence the
Western Aleutians bringing widespread northerly flow and making
things relatively mild this forecast period.

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

Beginning the extended forecast period Sunday evening, there will
be an exiting dynamic arctic trough moving east through the Gulf
of Alaska with a series of smaller scale troughs extending from
the North Pacific to the Bering Sea. Showers and rain will be
ending across most of Southern Alaska as offshore flow ramps up as
the upper wind regime becomes more westerly behind the departing
trough. Rather quiescent weather with mostly diurnal showers and
clouds looks to dominate through early Wednesday before the
pattern amplifies once again. It seems rather likely that another
arctic trough will dig into the Eastern Bering Sea and merge with
a southern stream trough over the Western Bering Sea, setting in
motion another period of wet weather as Alaska quickly transitions
into the typical wetter pattern for mid-August.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
LONG TERM...JA