Small Craft Advisory 927, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 PM AKST Fri Nov 23 2018

.ANALYSIS AND UPPER LEVELS...
High pressure lingers over Southcentral Alaska ahead of a front
that is moving through the Bristol Bay area as it tracks to the
northeast. Higher level cloud cover is already moving in over
Southcentral Alaska out ahead of the front. South of the Gulf,
a low has formed along the front and is now progressing north
towards the Gulf as it deepens. Out west the parent low of the
front moving through Southwest Alaska is over the central
Aleutians and is weakening as it slowly pushes south.

&&

.MODEL DISCUSSION...
The models have been struggling with the multiple lows moving
through this pattern and they continue to do so today. There is
somewhat better agreement with a low tracking through the Gulf
Saturday but they still differ with when and were the low center
will make landfall along the north Gulf coast which will have an
impact on timing and intensity of winds in the area. There is also
disagreement with multiple lows south of the Aleutians and where
those lows will move. Specifically, there are large discrepancies
with a low that will be somewhere south of the Alaska Peninsula on
Sunday. Some solutions have the low near the southern end of
Kodiak Island while others have it much further south.

&&

.AVIATION...
PANC...VFR conditions will persist until through at least
00Z/Nov 25th (3pm Saturday). Light snow will then spread over
the mountains, though a robust northerly wind at the surface may
maintain enough dry low level air to keep precipitation as virga.
Will maintain VFR ceilings for now, but hint at lowering ceilings
as snow moves into the area.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
through Sunday)...

A strong area of low pressure and a front following right behind
it are forecast to make their way quickly northward across the
Gulf and into Southcentral over the next couple days. As they
approach the area, they are both expected to bring strong winds,
heavy rain, and much warmer air to the area. Rain has already
begun in Kodiak associated with the low. As it tracks northward,
it is expected to peak in intensity as it moves over the offshore
Gulf waters Saturday afternoon, then make landfall somewhere over
the Kenai Peninsula Saturday evening. There remains significant
uncertainty with the low track, which in turn has very large
implications for the impacts that will occur as a result. The
going forecast takes the low over Seward, which if it occurs will
result in very strong winds through Passage Canal, Turnagain Arm,
and to a somewhat lesser extent, the Anchorage Hillside. A High
Wind Watch is in effect for the eastern Turnagain Arm for wind
gusts of 75 to 85 mph, which is currently most likely to occur
between 8pm and 2am Saturday night. For Passage Canal and the
Hillside, gusts of 55 to 65 mph are possible. In addition, after
the low passes, the gusty northerly winds through Seward and
Resurrection Bay will quickly shift even stronger out of the south
for a few hours Saturday night. Occasionally heavy rain is
expected all along the coast with this low as warm air moves in
behind it. As that low tracks inland, the warm air will have a
difficult time making it inland along with it initially, which in
turn may make for a brief period of snow showers for the western
Kenai Peninsula, Anchorage, and the Mat-Su Valleys Saturday
evening.

Several other models take the low center further east, along the
western Prince William Sound. This would significantly reduce the
impacts as far as winds go through Passage Canal and Turnagain
Arm, and instead result in the northerly winds increasing further
through Resurrection Bay and Seward, while on the other side of
the low, there would be potential for the low to push a strong
barrier jet into Cordova and the eastern Prince William Sound as
strong southerly winds help to push the barrier jet into the
coast. If this occurs there may be warning level winds in Cordova.

Behind the low there will be a brief relaxation of the winds for
Sunday morning before another strong front barrels into the Gulf
Coast. There is potential for winds to once again increase to
similar levels as Saturday night again on Sunday afternoon as that
feature moves in for the Gulf Coast, Prince William Sound, and
Turnagain Arm and higher elevations. What is more certain is the
front will reinforce the warm air during the day Sunday, allowing
it to infiltrate well inland, resulting in rising snow levels and
chances for plain rain even past Talkeetna as temperatures warm to
around 40 degrees Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

Snow is falling from Kuskokwim Bay to King Salmon this evening as
a front continues its northward progression from the AKPEN toward
the southwest mainland. An upper level disturbance sliding along
the coast will help to ratchet up the gusty winds along the coast
overnight as well as drive the front inland before dissipating
tomorrow afternoon. A Winter Weather Advisory remains in effect
through noon Saturday for the north Bristol Bay area with
generally 4 to 8 inches of snow expected from Dillingham to
Togiak with locally higher amount inland around the Kilbuck
Mountains.

The forecast then becomes quite challenging as a fast-moving
North Pacific low races north toward the AKPEN late Saturday. This
system looks to spin up a secondary area low pressure along its
occluding front by early Sunday, with this new low positioned
southwest of Kodiak Island. Its warm front is then expected to
push along the AKPEN early Sunday morning and over Bristol Bay by
midday Sunday. A strong southerly flow accompanying this boundary
means this system will advect a much warmer airmass (850mb temps
approaching 0 deg C) over the region on Sunday. At the surface, a
northeasterly wind will keep temperatures at the surface below
freezing for the onset of this event. Precipitation should begin
as all snow for the southwest mainland, but quickly change over
to rain from Iliamna south along the AKPEN as downsloping winds
off the Aleutian and Alaska Ranges help mix the warmer air down to
the surface. It is a different story farther north and west,
where the colder air at the surface will remain in place for the
longer period of time. This will result in a changeover to a
wintry mix of snow/sleet/freezing rain by late Sunday after some
initial light snow accumulations for locations along the north
Bristol Bay coast northeast to Sleetmute. Here, upwards of a
tenth of and inch of freezing rain could fall before temperatures
warm to above freezing late Sunday night. The warmer air will have
a harder time making it over the Kilbuck Mountains as it runs
into a second system anchored near Nunivak Island advecting colder
air south over the eastern Bering. Therefore, snow should remain
the dominant precipitation type across the lower Kuskokwim Delta
where only light accumulations are expected.

No advisories have yet been issued with this next system, as there
is still quite a bit of uncertainty with timing and strength of
the warm air advection. This will be re-evaluated by the night
crew when the latest suite of forecast guidance becomes
available.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

A series of North Pacific lows will continue to dominate the
weather over the Bering through the weekend as the region remains
under a broad cyclonic flow. Expect frequent directional wind
changes with these actively moving systems. Cold air advects back
across the western half of the Bering during the latter part of
the weekend as the parent low over the central Aleutians moves
south and the next low dives across the Bering Strait. Farther
west, a developing Kamchatka low will move toward the western
Aleutians by Monday.

&&

.LONG TERM FORECAST (Days 3 through 7: Monday Nov 26th through
Friday Nov 30th)...

The forecast period commences with the longwave trough across the
Bering and the North Pacific with a ridge axis over the Western
Aleutians. At the onset of the forecast period, the models
generally ping into the same features however, there are some
timing and tracking issues. The most glaring difference is with
the low entering the Gulf Of Alaska on Monday. The GFS and ECMWF
are about 350 NM apart with the placement of the surface low
south of Kodiak and the ECMWF being the most southerly solution
for this storm. Overall, it looks like an unsettle pattern for
both the Bering and the Gulf Of Alaska. Also noteworthy is the
emergence of the "Atmospheric River" in the Gulf Of Alaska. The
current thinking is that the bulk of the "Atmospheric River" will
move into Southeast Alaska, and Southcentral will only get a
portion of the moisture plume. The pops were bumped up again this
forecast package for the Prince William Sound Region. In addition
to the moisture, this system has a tight pressure gradient
associated with it, gusty winds expected in some inland locations
as well as over the water.

All the while, an assembly of lows from the Sea Of Okhotsk and
Bering are depicted in the operational runs of the global models.
The first is anticipated late Monday and Tuesday. The GFS is a
skosh quicker bringing this low eastward, but both the GFS and
the ECMWF place the track directly over the Chain. In its wake a
weak ridge axis will push across the Aleutians. Last but not
least, a cyclone will move out of the Sea Of Okhotsk and into the
Western Bering late in the period. But given the run to run
consistency issues only minor adjustments for the later portion of
this forecast package, as we all wait for the details of these
cyclones to flesh out.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 125.
		 Winter Weather Advisory 161.
MARINE...Storm Warning 119 120 125 130 131 139.
 Gale Warning 121 127 128 129 132 140 150 155 172 173 174 175 176
177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...PS