Small Craft Advisory 365, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 AM AKDT Fri May 10 2019

.ANALYSIS AND UPPER LEVELS...
A powerful low pressure system (especially for this time of year)
is moving north through the Gulf of Alaska. The well wrapped
center of this low is currently located along the eastern coast of
Kodiak Island, with its frontal systems just approaching the
southcentral coast. Of note, the moisture stream helping to fuel
this system stretches south all the way into the central Pacific.
This stream of moisture is resulting in plenty of rain as the low
moves inland. Showers are present in southwest AK wrapping around
the backside of the low, while a band of heavier rain is
currently (as of 4AM local time) approaching the southcentral
coast.

Winds associated with this system have already begun to increase
along Turnagain Arm and some buoy locations near the Barren
Islands. Overnight adjustments were made to the forecast in order
to capture these stronger wind speeds. Details in relation to the
models are below.

&&

.MODEL DISCUSSION...
Models seem to be in good agreement for the short term. They are
performing well on the track of the incoming low pressure system.
However, models seem to have underestimated the strength of the
incoming low. This is based on early observations from buoy data
reporting stronger than anticipated winds and the Turnagain winds
already gusting around 50 mph. This will have to be closely
watched ast the low approaches, as additional adjustments to the
forecast may be necessary.

&&

.AVIATION...
PANC...Ceilings and visibility will remain VFR for the TAF period.
Winds associated with an incoming frontal system will create very
strong surface winds. Mountain wave turbulence is expected over
and in the vicinity of the airfield. Strongest winds and turbulence
will be this afternoon into the evening hours.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Fri and
Sat)...
A windy day is in store for all of Southcentral AK. A modestly
strong area of low pressure is down to about 985 mb this morning.
It is crossing over Kodiak Island early this morning and tracking
quickly to the north. The system will maintain its strength as it
pushes through the AK Range this afternoon. The pressure gradient
will continue to tighten across the area and winds will ramp up
through the day, especially out of southeast to northwest oriented
terrain (Turnagain and Knik Arm, etc). The strongest winds will
likely hug the Turnagain Arm and the Anchorage Hillside. However,
as the low center itself moves north of Anchorage, southeast
winds will overspread all of the Anchorage Bowl. Gusts will be
able to exceed 50 mph late this afternoon into the early evening.
There is some indication that some mountain wave activity could
set up with this dynamic low. Coupled with some instability here
in early May, there could be some erratic stronger gusts if the
mountain waves happen to break over the lower elevations.

The other story with this system will be very heavy precipitation
along coastal areas. An area of deep-subtropical moisture is being
pulled north with the low. While it won't be an overly expansive
(west to east) area of QPF, if the proverbial "firehose" lines up
near Seward and lingers there into Sat morning, several inches of
rain are possible. We will continue to monitor this component
closely.

Saturday will remain breezy and cool across the entire area.
Southwest flow and some upper level energy will make for numerous
showers. Steady rainfall will continue for portions of the coast
with the heaviest rainfall amounts shifting over to the Eastern
portion of Prince William

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The frontal system currently stretched across Southwest Alaska
will continue to swing slowly to the west today as its parent
surface low just to the west of Kodiak Island turns to the
northwest and tracks across the mountains and into Southwest
Alaska early this afternoon. The low will then slowly continue to
the northwest through the afternoon and evening, changing steady
rain over to showers. Isolated thunderstorms are possible as well
this afternoon and evening over the lower Kuskokwim valley and
Kilbuck Mountains. Showers will continue across the area tonight
through Saturday before diminishing somewhat Saturday night.
Another frontal wave will lift in from the southeast,
reinvigorating showers Sunday and Sunday night, particularly
along the coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A large upper level low remains stretched across the Bering with
one center located over the southcentral Bering and a second
center associated with the low near Kodiak Island. The central
Bering upper low will swing to the southeast and over the eastern
Aleutians tonight and as the more eastern low rotates northwest
across Southwest Alaska and broadens into a more diffuse trough.
The main upper low center will continue slowly to the east along
the Alaska Peninsula Saturday and Sunday with troughing remaining
over the central and eastern Bering.

&&

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

A North Pacific low lifts northward over the Alaska Peninsula and
into the eastern Bering on Sunday. Small craft winds are expected
in the southwestern Gulf of Alaska beginning Sat evening. Winds
will diminish by Sun afternoon. There is high confidence a broad
area of weak low pressure will remain over the Bering through Tue
with no significant winds or waves expected. Meanwhile, a second,
weaker North Pacific low approaches the Gulf Mon evening. At this
time, no significant winds or waves are expected for the Gulf of
Alaska through Tue.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

The long term trend includes a broad upper level trough over the
eastern Bering with a ridge over the Alaska-Yukon border. By
Tuesday, the area of high pressure shifts over the northern half
of the state, allowing the trough to extend all the way over the
central Gulf. Models struggle to resolve how these two features
will interact, however there is a growing consensus that a series
of upper level shortwaves will rotate around the trough and lift
over the southern Mainland through Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101
MARINE...STORM: 352
         GALE:  119 120 125 129 131 132 150 155 351
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
MARINE/LONG TERM...JPW