Small Craft Advisory 850, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKST Sat Nov 7 2020

.ANALYSIS AND UPPER LEVELS...
The upper level ridge has now amplified over the eastern Gulf and
AlCan border this afternoon with strong southerly flow riding up
the jet stream on the ridge's western flank. As expected, a
surface low has developed near the Alaska Peninsula this
afternoon which is in the rear inflow sector of the jet stream as
the jet intensifies over the northern part of the ridge. This is
the main low that will track into the Southwest Alaska mainland
overnight. This farther west track is bringing in warmer air to
Southcentral Alaska and Southwest mainland Alaska as well.

&&

.MODEL DISCUSSION...
Models are now in good agreement with the low moving into southern
Alaska taking a more northwesterly track and developing a triple
point low in Cook Inlet later than on previous runs. That has
shifted the forecasts to a warmer solution overall.

Models then remain in good synoptic agreement with the low
moving through the western to northern part of the Bering Sea
Sunday through Monday night. The next low that approaches the
southern Bering Sea on Monday night is seeing considerable spread
in model track and strength which is causing increased uncertainty
for the Aleutians through southwest mainland Alaska for the
middle of next week.

&&

.AVIATION...
PANC...Wind shear will be prevalent as winds aloft will be strong
from the southeast with north-to-northwest winds at the surface.
This could develop into one of those wind shear situations where
the direction in the shear layer could be approaching 180 degrees
opposite directions.

MVFR conditions should prevail overnight and through Sunday with
some periods of IFR possible as snow and then rain move through
the terminal area. Snow should turn to rain after midnight and
then there may be a switch back to snow Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3):

The longwave pattern features a dirty ridge over Southcentral.
With the impulses of shortwave energy embedded in this dirty
ridge, cloud coverage and flurries/snow anticipated today
depending on which part of Southcentral you reside in. A strong
North Pacific low moving is racing towards Southcentral and will
push that ridge axis to the east, and Southcentral will get a
full-fledged cyclone. This storm will make for very active weather
across Southcentral this weekend. The confidence is high and a
Winter Storm Warning was issued for the Susitna Valley. The
Susitna Valley may get 9-20 inches of snow mainly from Talkeetna
north and west. A Winter Weather Advisory for the Richardson
Highway and areas north of Glennallen was issued for snow and
begins tonight at 9 PM AKST through 9 PM AKST Sunday night. The
pressure gradient will be strong with this storm. Additionally, a
High Wind Warning is in effect for Turnagain Arm and higher
elevations for wind gusts to 75 mph tonight.

The surface low will move across Seward and Chenega Sunday
morning. The latest runs of the models do show a pocket of warmer
air in the boundary layer along Cook Inlet. The potential for a
rain/snow mix or sleet is possible for the Anchorage Bowl on
Sunday. Very strong pressure rises along the Kenai Mountains and
Prince William Sound will cause strong winds. With a fresh blanket
of snow and gusty winds Thompson Pass can anticipate blowing snow
Sunday and Monday. As this system evolves, moderate to heavy snow
across the Copper River Basin could result in over a foot of new
snow accumulation from Sunday and potentially lasting into Monday
morning.

By Monday 12z (3 AM AKST), the surface low will be northeast of
Yakutat and a ridge axis will be spanning from the AKPEN to
Dillingham to McGrath. The pressure gradient again will be tight
and widespread northerly flow is projected for the Gulf Of Alaska.
By Tuesday 00z (3 PM AKST) that ridge axis will be directly over
Kodiak and Skwentna. However, this ridge won't last long over
Southcentral as the models bring a new front into the western Gulf
early Wednesday.

&&

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

A low tracking over Bristol Bay is currently bringing steady
precipitation across nearly all of Southwest Alaska. Rain is
expected to continue through the evening across the Bristol Bay
coast and Kuskokwim Delta. With the track slightly farther north,
temperatures are a couple degrees warmer that expected in the
Middle Kuskokwim Valley. As such, rain is also occurring from
Sleetmute westward through Aniak. While precipitation in this
area is expected to change to snow and persist through Sunday
morning, the current rain will cut into the snowfall totals,
though isolated amounts of up to a foot remain possible. Rain will
also change to snow farther west over the portions of the
Kuskokwim Valley as the low departs over Southcentral, thus
turning winds due north and advecting in colder air. However,
accumulations will be minimal.

Skies will partially clear overnight Sunday into Monday under a
weak ridge. A front will move onshore over the Kuskokwim Delta
Monday morning and remain nearly stationary through Tuesday
morning. Any snow would be brief ahead of the front given the
strong southwest flow. Coastal flooding remains possible, though
winds are not overly impressive and tides will be low (mid-range
gales). The Bristol Bay and interior regions will remain dry over
this time. Another, stronger front will move onshore over all of
Southwest Alaska. It is somewhat too early to determine
precipitation type, however as usual, it looks to be more rain
along the coast with mixing or snow inland.

&&

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

Rain will continue generally east of Unalaska tapering off
through the evening as the associated low departs to the
northwest. Quiet conditions will persist through Tuesday morning
under a weak ridge. A front will track eastward across the western
and central Aleutians bringing moderate rain and gusty southerly
winds Sunday afternoon through Monday night as a low moves over
the western Bering. Rain will develop over the entire
Bering/Aleutians/Pribilofs by Tuesday as a double-barrel low
tracks into the central Bering.

&&

.MARINE (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska:

A frontal system from the North Pacific will usher gales
southeast of Kodiak and offshore starting Tuesday night. As this
front moves east-northeast, the gales will be following closely
too along the frontal axis and west of the frontal boundary across
the Gulf through Wednesday morning. A long period fetch from
south of the Aleutians will approach the southwestern Gulf by late
Wednesday afternoon into Wednesday night. This will generate
hazardous wave heights peaking to near 27 ft late Wednesday night.
Wave heights near the frontal boundary are expected to remain
near 12 to 15 ft with higher sets.

Bering Sea:

A couple of lows connected to a frontal boundary from the
Northwest Pacific will bring gales and storm force winds
across the Aleutians, central and eastern Bering starting
Tuesday morning through Wednesday afternoon. One of the lows will
break away and trek eastward toward Bristol Bay on Wednesday
morning. Meanwhile, a parent low linked to the frontal zone
moves northward then curves south of Saint Lawrence Island before
descending southward Friday night. Dangerous wave heights between
25 to 35 feet with potentially higher sets will stay south of the
Aleutians and the central Bering through at least Wednesday
afternoon. Gales from the low over the eastern Bering
will gradually wane by Thursday night to small craft conditions.

&&

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

Synoptically, a broad longwave trough will exist from the
Kamchatka Peninsula to the west coast of Alaska with ridging over
the Gulf and Alaska mainland. The dominant feature to watch in
the first half of the forecast period is a negatively tilted
trough over the AKPEN on Wednesday. Given the broad southerly flow
and tropical moisture feed within the warm conveyor belt of the
system, warm temperatures and rain are expected over southern
Alaska on Tuesday and Wednesday. Snow is likely over Southwest
Alaska at elevations above approximately 3000 feet. For
Southcentral, the rain/snow line will be a difficult forecast
once again due to when, where, and if a triple point low sets up
in the northern Gulf along the warm front. However, at this time
lower elevations along the Gulf coast will likely be rain due to
little cold air in place as the front moves in.

Over the Bering, strong cold air advection is expected out of
eastern Russia, which will be reinforced by a nearly stationary
low over the Bering Strait. Most models now show gale to storm
force winds over the central Aleutian Chain on Wednesday. On
Thursday the main shortwave trough mentioned earlier is expected
to move into the eastern Gulf, which should allow for clearer and
colder conditions over the southern mainland through Saturday.
Over the AKPEN, Bering, and Aleutian Chain, strong west to
northwest winds and rain are expected through Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 145.
		 Winter Weather Advisory 141.
		 High Wind Warning 101.
MARINE...Storm Warning 119 120 130 131 175 176 351 413.
		 Gale Warning 125 128 132 136-139 141 150 155 160 165
	                  170 173 174 177-179 181 185 352 411 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...CB/CJ

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1124 PM AKST SAT NOV 7 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1106 PM     SNOW             7 SE TALKEETNA          62.27N 149.94W
11/07/2020  M2.0 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SMALL FLAKES, TEMPERATURE IS 22F.

0944 PM     SNOW             3 E KENAI               60.57N 151.08W
11/07/2020  M4.0 INCH        KENAI PENINSULA    AK   TRAINED SPOTTER

&&