Small Craft Advisory 859, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
519 AM AKST Wed Nov 11 2020

.ANALYSIS AND UPPER LEVELS...

The subtropical jetstream continues to remain south of 50N west
of 150W, then curves northward to over the AlCan border. A large
area of low pressure located in the left-exit region of this jet
is currently over the eastern Bering is moving northeastward
towards the Kuskokwim Delta and northern Bristol Bay. This low is
also gradually weakening as it becomes more vertically stacked as
well as it becomes more decoupled from the core of the jet. A
negatively-tilted trough currently extends from the center of the
aforementioned low through the central Gulf of Alaska. A triple
point low is developing over Kodiak Island and is moving
northeastward towards the Kenai Peninsula.

Closer to the surface, radar imagery shows precipitation moving
northeastward across Cook Inlet into the Mat-Su Valley, Kenai
Peninsula, Bristol Bay and the Kuskokwim Delta. There are a
variety of precipitation types across the area. Warmer locations
over the water and along the coast of the western Kenai Peninsula,
precipitation is falling as rain. Farther inland across lower
elevations (including portions of the Anchorage Bowl),
precipitation is currently freezing rain. Snow is falling over the
Kenai Mountains and across the Susitna Valley as temperatures
remain cold enough at the surface and in the mid-levels. Across
Southwest Alaska, radar imagery shows rain showers over the
Kuskokwim Delta as temperatures remain above freezing. Snow
showers are over the Ahlkun and Kilbuck Mountains as temperatures
are below freezing in these locations.

&&

.MODEL DISCUSSION...

Guidance seems to be in good agreement with the placement and
orientation of synoptic scale features at the surface and in the
upper levels through Friday afternoon. Discrepancies increase
Friday evening as models begin showing different solutions for the
placement of the surface lows. Confidence is above average through
Friday afternoon and moderate for Friday evening through Saturday.
High resolution models were favored for local effects.

&&

.AVIATION...
PANC...VFR conditons will prevail until 21z. Snow showers moving
through the area through 16z can reduce conditions to IFR as
ceilings are expected to drop near 500ft. Strong directional low-level
wind shear will continue until 21z. MVFR conditions will prevail
from 21z Wednesday through 18z Thursday as celings remain between
1000-300ft.

&&

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

A strong front is tracking across the Gulf of Alaska and bending
back into Southcentral Alaska this morning. This is bringing
rainfall to the coastal area, though much of the lee side of the
coast mountain ranges are downsloping.
The winds coming through the mountains are causing a large range
of temperature differences over short distances. An example is
how early this morning the winds through the Knik River are in the
mid 40s while the winds out of the Matanuska river are in the mid
20s. This is causing the Palmer area to see temperatures
fluctuate wildly this morning. Anchorage is keeping a more
northwesterly wind which has kept the temperatures in the lower
elevations below freezing all night. This may be a set up for some
freezing rain this morning before the upper level trough moves
through from the south and brings in colder air aloft which should
then turn precipitation back to snow.

This cold air aloft is quite strong and destabilizing the
atmosphere behind the front. An area of thunderstorms caused by
this cold air aloft has been tracking south of the Alaska
Peninsula overnight and may bring a few thunderstorms into the
Gulf of Alaska today.

Another cold upper level low will move from southwest Alaska into
SOuthcentral tonight into Thursday. This will keep the potential
for some snow showers around through Thursday. After that, there
should be a cooling and drying trend over Southcentral into the
weekend.

&&

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

The next anticipated low pressure is just pulling ashore in
Southwest Alaska, with the low center over Kuskokwim Bay and
headed northeast. It is producing some showery precipitation
along coastal areas, with a detached occluded front over Interior
SW. This low will push inland today and then be absorbed by a
broad area of low pressure sitting over mainland AK. This broad
low is stagnant, which will keep weather in Southwest AK unsettled
through the rest of the week. So expect continued showery
precipitation. Another low moving across the Bering will approach
the Southwest Coast on Friday, but models have not discerned much
regarding that system yet, so stay tuned there.

Regarding the Coastal Flood Advisory for the Bristol Bay Coast, it
remains in effect with strong winds associated with the current
low pushing towards the coast. The highest tide and highest potential
water rises should have occurred overnight, but with strong winds
continuing the threat is not over. Therefore, left the advisory
out. So, please continue to monitor this situation if you are
along the Bristol Bay Coast.

&&

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

A matured, well wrapped occluded system is currently moving
through the Eastern Bering and just about to move onshore. A tight
pressure gradient with cold air advection on the backside of this
low is producing storm force winds in the Eastern Bering, verified
earlier this evening by observations at St. Paul Island and ASCAT
imagery. This means the forecast continues to be on track for
windy conditions in the Bering.

This low will exit the Bering today, but strong north to
northwesterly flow will remain behind it. Cold air advection will
be present with it, which will change the precipitation type to
snow over the Bering by Friday. With cold air moving in, upped
wind speeds in the Eastern Bering and South of the Eastern
Aleutians/AK Peninsula into Friday. On Friday, the next low
pressure system will move into the Western Bering from Eastern
Siberia, taking a different track from the lows so far this week.
This will keep winds out of the north and temperatures cooler.
Models are still deciding what to do about this low, so stayed
tuned over the next couple of days.

&&

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

Gulf of Alaska:

A Northern Gulf low drifts eastward through Sun. While track and
development of the low varies, easterly small craft winds linger
along coastal waters through Fri.  Confidence is good for
widespread westerly high- end gale force winds and waves from the
Alaska Peninsula across the Gulf to diminish on Sat. A new front
crosses the Alaska Peninsula Sat with northwesterly small craft
and local gale force winds near channeled areas entering the
Western Gulf Sun.

Bering Sea:

A polar front sweeps south over the Bering through Sat.
Confidence is good for widespread small craft winds and waves over
the Bering with local gale force winds with a St Matthew Island
low Fri that crosses the Eastern Aleutians Sat, and all parts
diminishing through Sun. A well-developed front approaches the
Western Aleutians and Bering Sat. Increasing confidence for
widespread southerly high-end gale force winds developing across
the Western Aleutians and Bering through Sun.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

On Saturday the primary feature will be a highly amplified upper ridge
developing across eastern Siberia into the far western Bering.
Ahead of this ridge, strong northerly flow and cold advection
looks to set up across the Bering, Aleutians and western coastal
areas. Expect this northerly flow to bring widespread snow showers
across the Bering/Aleutians and western coastal areas along with
gusty winds, especially through the gaps in the Aleutians. On
Sunday, this northerly flow will weaken as a storm system
approaches the far western Aleutians. This storm will bring a
return to southerly winds and warmer temperatures for the Western
Aleutians while another cold system starts to approach the Bering
Strait region.

Fairly quiet weather will be found across the mainland through
the weekend outside of a few snow showers along the Northern Gulf
Coast. Offshore winds could be a bit breezy in some of the local
gaps across Southcentral. Temperatures could fall slightly below
normal (Anchorage-High 27F, Low 15F) for mid- November with clear
skies.

For Monday and Tuesday, high pressure looks to park over mainland
Alaska, with a broad/weak low in the Gulf. This should result in
mostly dry weather, with the main risks being for occasional
strong winds along the Northern Gulf Coast due to a cold airmass
remaining in the Copper River Basin and a continued moderate
pressure gradient along the Northern Gulf Coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 125 130 131 132 136 137 138 160 173 174
180 181 185 351 352 412 413.
Storm Warning 150 155 165 170 171 172 179 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...MK/BG

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1053 AM AKST Wed Nov 11 2020

AKZ101-120600-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1053 AM AKST Wed Nov 11 2020

...A WINTERY MIX ACROSS THE ANCHORAGE BOWL THIS AFTERNOON THROUGH
EARLY EVENING...

A weakening weather front heads north this afternoon and will
bring a more steady wintery mix of precipitation across the
Anchorage Bowl. Moisture will generally fall as snow, but will mix
and possibly a few pockets of light freezing rain times before
tapering off this evening. Some light snow accumulations, an inch
or less, are also possible. Motorists should expect winter driving
conditions and allow extra for travel.

SPECIAL WEATHER STATEMENT...CORRECTED
National Weather Service ANCHORAGE AK
1105 AM AKST Wed Nov 11 2020

AKZ101-120600-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1105 AM AKST Wed Nov 11 2020

...A WINTERY MIX ACROSS THE ANCHORAGE BOWL THIS AFTERNOON THROUGH
EARLY EVENING...

A weakening weather front heads north this afternoon and will
bring a more steady wintery mix of precipitation across the
Anchorage Bowl. Moisture will generally fall as snow, but will mix
and possibly a few pockets of light freezing rain times before
tapering off this evening. Some light snow accumulations, an inch
or less, are also possible. Motorists should expect winter driving
conditions and allow extra time for travel.