Gale Warning 411, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKDT Sat Sep 14 2019

.ANALYSIS AND UPPER LEVELS...
Today is the break in between systems as an upper level ridge
builds over the mainland part of the state. The low that has been
in the Bering Sea for days has now kicked southeast and is now in
the far southeast Gulf of Alaska. The next low is in the Western
Bering Sea and moving eastward rather quickly. The jet stream is
helping to move things along as the 250 mb jet is over 150 kt as
it moves through the Bering Sea, southwest mainland Alaska and
through the Gulf of Alaska.

&&

.MODEL DISCUSSION...
Overall there is good agreement with the models into early next
week. There are some subtle differences in the expected amount of
downsloping on the models. That are impacting the amount of QPF on
the lee side of the mountain ranges, but it does look overall like
the downsloping will be minimal in part due to the amount of
moisture in the system.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through
tonight. Turnagain Arm winds will be present on Sunday morning
into the afternoon. This could bring some gusty southeast conditions
into the terminal for a few hours, but confidence in the exact
timing is low. Rain will move in to the area around noon on Sunday
and may bring ceilings down to the MVFR level.

&&

.FIRE WEATHER...

Most of Southcentral will see wetting rains with the system moving
in on Sunday. Gusty southeast winds will also develop through the
typical gaps, to include Turnagain and Knik Arms and the Copper
River Valley.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Offshore flow and diminishing cloud cover will prevail tonight as
a low in the Gulf exits to the southeast. Sunday will bring a
return to wet weather, as a low in the Bering pushes eastward.
Expect a triple point low to form south of the parent low.
Enhanced southeast gap winds are likely along Turnagain Arm and
the Knik River Valley Sunday morning, then in the Copper River
Valley Sunday afternoon as the east to west pressure gradient
increases. Despite southeast flow at the surface, the upper low
should maintain steady south/southwest winds aloft. Thus,
confidence is high that precipitation will be widespread, and even
areas that are frequently shadowed, including Anchorage and the
eastern Kenai Peninsula, will see up to a half inch of rain
by Sunday night.

The parent low will shift eastward through the Gulf Monday, and
the main area of showers will pull east as well. Shortwaves
rotating around the backside of the low could bring some showers
to the Copper River Basin, but in general a drying trend will be
underway Monday as a ridge begins to build over Southwest AK.

As for marine weather, widespread small craft advisory level
winds and seas are expected in the Gulf Sunday into Monday.
Highest winds and seas will initially be in the western Gulf, then
spread to the eastern Gulf by Sunday evening as the surface low
tracks eastward. In addition, a gale force barrier jet is
expected along the north Gulf coast, east of Prince William
Sound. Areas of gales are likely as early as Sunday night, as
cold northwest flow wraps around the backside of the low and
enhances the pressure gradient.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-2: Sat-Mon)...

The stacked low pressure system over the central Bering pushes
eastward overnight with the associated front moving inland across
the Southwest this evening. This system slows down as is moves
across land which will result in rain accumulations between one
half to one inch, with locally higher amounts. Light onshore flow
this evening will be variable on Sunday. In the wake of this
system the general flow will be from the north. The next front is
quick to follow with the boundary expected to push to the
Southwest coast early Tuesday morning...spreading inland through
the afternoon. This system will bring another round of appreciable
rainfall...especially for Bristol Bay and the Kuskokwim Valley
late Tuesday into Wednesday as the subtropical jet noses across
from the eastern Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

An active weather pattern is in store through Tuesday as one
storm system currently over the Bering is followed by the next
system Sunday night. The low currently over the Bering tracks
eastward tonight, passing over Saint Matthew Island by early
Sunday morning. The associated front will bring southerly small
craft winds and widespread rain across the central and eastern
waters through early Sunday morning before tapering off.

The next low pushes a front to the Central and Western Aleutians
Sunday night. Winds and precipitation chances were increased for
much of the the Bering locations as models trend toward better
agreement on the strength and track of this system through
Tuesday. The 997 mb low driving the front crosses over the
Central Aleutians by Monday afternoon and tracks to the Pribilof
Islands at 991 mb Tuesday afternoon.

&&

.MARINE (Days 3 through 5)...
There is high confidence of a low moving through the Central
Bering on Tuesday that will bring gale force winds to the area. As
the low tracks to the east and weakens, winds will diminish for
the Bering and Gulf. There is good confidence that another low
will approach the Aleutians Wednesday into Thursday and that it
will bring small craft winds to the islands.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Models are starting to fall in line with the system tracking
across the Bering Tuesday and there is now good agreement of
widespread rain for southern Alaska Tuesday and Wednesday. On
Wednesday another low approaches the western Aleutians from the
North Pacific with it expected to stay south of the Aleutians
through Thursday while it tracks to the east. Thursday night the
models struggle with what to do with this system, lowering
confidence heading towards the weekend. Because of this the
ensembles were preferred by the end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 150-160, 172, 177, 352, 132.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ/MSO
SOUTHCENTRAL ALASKA...MM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
MARINE/LONG TERM...DK