Gale Warning 510, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 PM AKDT Sat Oct 26 2019

.ANALYSIS AND UPPER LEVELS...
The large 975 mb low near Adak, which is extra-tropical remnant
of former-typhoon Neoguri, is weakening as it slowly heads
eastward. The jet stream is running between this low and a strong
ridge in the eastern Gulf of Alaska and reaching into the Chukchi
Sea. This is also bringing a tap of tropical moisture from south
of 30N and transporting it into the state. This jet will be slow
to move eastward and is the focal point for additional waves to
develop and move along the front associated with the main low.

&&

.MODEL DISCUSSION...
Models are in good overall agreement on the synoptic scale, but
there are other model differences that are important to note. The
first is that the GFS model has consistently been the strongest
with the strength of the winds along the front impacting
Southwest and Southcentral Alaska. These higher winds have not
verified over the past few days so the wind strengths reflected
on the NAM and some of the high resolution models were preferred
to the GFS.

&&

.AVIATION...
PANC...VFR conditions should persist through the TAF period even
with the strong front moving into the region. The winds at
mountaintop level should remain from the southeast which will
diminish the intensity of the rainfall over the terminal and
therefore limit the potential for MVFR ceilings or visibilities.

Winds are another matter as the wind situation is rather complex.
While it looks likely that the southeast surface winds out of
Turnagain Arm will move over the terminal, it is not a sure thing
and there is a chance light northwest winds could persist or come
and go due to the winds being in an eddy should the core of the
Turnagain Arm winds remain south of the terminal. This also would
greatly increase the magnitude wind shear over the airport
through this evening. Surface winds should bend to the northeast
overnight which will cause some low level wind shear into Sunday.

&&

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

An atmospheric river currently bringing moderate to heavy
precipitation to the AKPEN and Kodiak Island will continue
shifting eastward tonight into tomorrow. Snow will continue
tonight in the northern Susitna Valley, including Broad Pass. A
winter weather advisory remains in effect for this. By tomorrow
afternoon, the cold air in place will have eroded and snow will
change over the rain. Moderate to heavy precipitation will spread
into the eastern Kenai Peninsula late tonight into Sunday. A Flood
Advisory has been issued for the Seward area, with total
precipitation of 4 to 6 inches expected by late Monday. Elevated
winds over much of Southcentral are expected with this system. In
particular, expect gusts to 75 mph along Turnagain arm as the warm
front pushes into the Northern Gulf Sunday afternoon. With strong
cross-barrier flow, expect the usual lee-side areas to get
somewhat rain shadowed, including the western Kenai Peninsula, the
Anchorage Bowl, and Matanuska Valley. However, considering the
amount of moisture being drawn northward with tropical
connections, these areas should all see some rain Sunday... the
challenge is timing. In addition, as flow aloft veers to southerly
Monday, precipitation chance in the usual downslope areas should
be somewhat enhanced, and the forecast was updated to reflect
that.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
With low pressure to the west and ridging to the east, southwest
Alaska will keep southeast winds over the area through Monday. The
strongest winds will be tonight with gusts up to 65 MPH through
the Kamishak gap. The pressure gradient will weaken through Monday
diminishing winds across the area. This setup is also bringing an
abundance of moisture to southwest Alaska resulting in widespread
rain through Sunday with lighter rain on Monday. There is enough
warm air to expect rain around the area with the exception of the
some of the higher mountains.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Low pressure south of the central Aleutians will continue to bring
storm force winds to the western Bering and Aleutians through
early portions of tonight. Winds will then diminish through Sunday
as the low weakens and slowly tracks east. A triple point low that
will form near the Alaska Peninsula will track into the Bering
Sunday and absorb the other low. This will keep cyclonic flow over
the Bering with westerly winds expected over the Aleutians at
small craft levels. This setup will keep rain showers over most
locations through the forecast period.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

A North Pacific low approaching the south side of the Alaska
Peninsula Wednesday morning will produce gales in that area from
Wednesday into Thursday morning over the Gulf. A potential barrier
jet Thursday morning may also briefly produce gale force winds
Thursday morning. Elsewhere, gales are not expected through
Thursday in the Bering/Aleutians.

&&

.LONG TERM FORECAST (Days 3 through 7: Tuesday through Saturday)...

A surface trough of low pressure centered off the coast of the
Kuskokwim Delta will move inland Tuesday. Widespread shower
activity is expected out ahead of this feature, in both Southwest
and Southcentral. The approach of the low, despite its weakening,
will keep Turnagain Arm and Upper Hillside winds gusty through the
day, though without much else to speed up the winds, strong winds
are not expected.

The next North Pacific low will approach the Alaska Peninsula
early Wednesday morning. The low is expected to track northeast,
as associated rain tracks well ahead of the center of the low,
thanks in part to the remnants of the low that moves into Southern
Mainland Alaska. The low center tracks up Shelikof Strait on
Thursday, and becomes a diffuse area of low pressure over
Southcentral by Friday. Along this track, warm, wet, and windy
weather is likely to continue in Southcentral potentially into
Friday. As is typical for the long-term forecast, the details of
all of this are highly uncertain and will be refined in future
forecasts.

Despite the uncertainty in the details, the models are in decent
agreement that behind this low there will be a significant
pattern shift in the late Friday or Friday night period. The shift
will consist of significantly colder and drier weather with strong
outflow winds across Southern Alaska as an area of high pressure
builds in through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High wind warning 101, Flood advisory 125 Snow advisory 145.
MARINE...Storms 130 131 177 411.
         Gales 120 132 136 137 150 160 175 178 180 185 351 352 412 413.
FIRE WEATHER...NONE.

&&

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