Small Craft Advisory 1, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 PM AKST Tue Dec 31 2019

.ANALYSIS AND UPPER LEVELS...
A major upper level Arctic trough remains over southwest Alaska
and the eastern Bering Sea bringing very cold temperatures to
areas under it. South central Alaska is in the warm southerly
flow aloft ahead of this trough, but that will change over the
next day as a cut off low develops from this trough over Southwest
and Southcentral Alaska. At the surface, the main low is tracking
up Cook Inlet this evening and will move into the western Copper
River Basin overnight. Satellite imagery shows cold air cumulus
clouds streaming off the ice edge over the northern Bering Sea and
tracking over the central and eastern Bering Sea. These clouds
are bringing snow squalls to the eastern Bering to the eastern
Aleutians and Alaska Peninsula. Very cold air is also moving north
up Cook Inlet today and will move into the rest of south central
Alaska by Wednesday morning.

&&

.MODEL DISCUSSION...

Models are all in good alignment with the synoptic pattern as well
as the system moving through southwest and south central Alaska
through tomorrow. The differences mainly are due to model
resolution and ability to resolve small details. The NAM has been
doing a very good job with this storm and both it and the GFS seem
to have good timing on the cold front as it moves up Cook Inlet
this afternoon. After this system passes, models look to be locked
in good agreement through the weekend before some more notable
discrepancies creep in for early next week.

&&

.AVIATION...
PANC...The strong southeasterly winds will abruptly shift to the
southwest this evening as much colder air moves up Cook Inlet and
rapidly switches rain to snow sometime between 4Z to 6Z this
evening. Snow will likely be moderate-to-heavy in intensity for a
while with gusty winds producing IFR conditions. The biggest
challenge is forecasting the duration of this heavy snow, though
it should become light or end no later than 15Z.

&&

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

Low pressure currently located over Kodiak Island is continuing to
produce strong southerly flow and warm temperatures for much of
south central AK. However, cold air can be seen on satellite
streaming into the western Gulf of Alaska and surface observations
are indicating snow and cold air are now moving up Cook Inlet.
Blizzard conditions arrived as expected for the Homer area as
well. This means the forecast is on track for a sharp drop in
temperatures and 4-8 inches of snow for the Anchorage area
tonight. The Mat-Su Valley will also see snow tonight with highest
totals just under 6 inches in areas near Skwentna.

Both the Blizzard Warning and Winter Weather Advisory remain in
effect due to these conditions into tomorrow morning. After the
initial push of cold weather, light snow will linger through the
morning as temperatures continue to fall. The low pressure system
will then exit, but cloud cover is expected to linger keeping
temperatures steady in the single digits for much of south central
Alaska and Kodiak for the next couple of days. The exception is
the Copper River Basin where temperatures will continue to drop to
around 10 below zero by Friday.

&&

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

A deep upper level trough combined with an elongated low centered near
Kodiak Island is continuing to enhance snowfall over the Middle
Kuskokwim Valley. An additional 4 inches is likely over this area
through New Year's morning. Gusty northwesterly winds will lead
to periods of blowing snow as well. Farther west, a Wind Chill
Advisory remains in effect for the Kuskokwim Delta. Lows near -15
combined with the aforementioned winds will lead to wind chills
near -40. Snow will taper off and winds will gradually diminish
through the day Wednesday as a broad upper level low stalls over
Bristol Bay. Precipitation chances will be minimal on Thursday,
however temperatures will remain below zero across much of the
region.

&&

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

Northwesterly flow will persist across the central and eastern
Bering/Aleutians bringing widespread snow showers. Heavy freezing
spray is likely given the gusty winds combined with the very cold
airmass. A weak ridge will bring more settled weather across the
western Aleutians through Thursday.

&&

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

A relatively quiet weather pattern sets up for this time of year
all across Southern Alaska and the Bering. A low over the
southern Gulf of Alaska may get winds to gale force along the
North Gulf coast, southern Cook Inlet, the Barren Islands, and
Shelikof Strait on Friday. The low moves into the eastern Gulf of
Alaska Saturday, with a chance of some northwesterly gales through
the Barren Islands. A new North Pacific low may move into the
southern Gulf of Alaska on Sunday, but there is substantial model
disagreement, and confidence in that is low.

For the Bering, high pressure will keep all winds below gale force
all across the Bering Sea, with a possible exception of a dying
front over the western Aleutians early on Friday. Winds may
approach gale force in the western Aleutians Sunday night as a
strong low approaches.

&&

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

A much quieter weather pattern is setting up for much of Southern
Alaska in the long-term period as a cold air mass becomes firmly
entrenched across the area. This will divert the storm track from
being over us to instead staying south over the North Pacific with
any lows impacting the Panhandle. This is generally well-agreed
upon in the models.

With that said, there will still be a few storm systems that will
be worth watching. On Friday, a weak low will be centered off the
coast of Kodiak, over the southwestern Gulf. It will slowly move
eastward across the southern Gulf and into the eastern Gulf on
Saturday. Snow may impact Kodiak into Friday morning, though a
repeat of the near blizzard conditions of a few days ago does not
appear likely. On Sunday, a new North Pacific low may approach the
AK Pen and Kodiak, but there is poor model agreement on this.
There is much better agreement on the leading front of a strong
North Pacific low moving into the western Aleutians on Monday. The
front should slowly track across the southern Bering into
Tuesday.

Elsewhere, cold and dry will be the name of the game over mainland
Alaska, which means the main weather hazards will be strong gap
winds, particularly through Thompson Pass, but also possibly
through the Matanuska Valley. These winds coupled with the cold
air may lead to wind chill concerns, which unlike previous days,
will focus more on Southcentral, rather than Southwest Alaska.
Continued polar air pouring southward across the Bering on Friday
looks to diminish this weekend, to more light and variable winds.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 181 and 121. Snow Advisory 101. Flood Advisory 145.
Heavy Snow Warning 152. Wind Chill Advisory 155.
MARINE...Storm Warning 130  Gale Warning 131 132 138 139 150 155 160 165 172 179 180
181 185.
Heavy Freezing Spray Warning 130 131 132 136 137 138 139 140 141 150 160 165
179 180 181 185.
FIRE WEATHER...DONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...JW/CK

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1130 PM AKST TUE DEC 31 2019

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

1125 PM     SNOW             EAGLE RIVER             61.32N 149.54W
12/31/2019  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

&&

MSO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1153 PM AKST TUE DEC 31 2019

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

1152 PM     HEAVY SNOW       2 SW CAMPBELL           61.16N 149.94W
12/31/2019  M4.0 INCH        ANCHORAGE          AK   MESONET

1151 PM     HEAVY SNOW       8 MILES SSE EAGLE RIVER 61.24N 149.44W
12/31/2019  M4.4 INCH        ANCHORAGE          AK   NWS EMPLOYEE

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
146 AM AKST WED JAN 1 2020

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

1137 PM     SNOW             1 NW SOLDOTNA           60.50N 151.10W
12/31/2019  E2.5 INCH        KENAI PENINSULA    AK   NWS EMPLOYEE

            ESTIMATED BECAUSE OF BLOWING AND SETTLING.

0143 AM     SNOW             16 S KNIK               61.23N 149.80W
01/01/2020  M7.0 INCH        ANCHORAGE          AK   PUBLIC

1230 AM     SNOW             17 S KNIK               61.21N 149.77W
01/01/2020  M4.6 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            ESTIMATED ANOTHER 2-4 INCHES MORE AT BIVOUAC
            TRAILHEADS OFF CAMPBELL AIRSTRIP RD.

&&