Gale Warning 689, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
740 AM AKST Wed Dec 25 2019

.ANALYSIS AND UPPER LEVELS...

The upper level trough responsible for the Christmas Eve snow in
Southcentral AK has lifted to the northeast. Snow continues in the
Mat-Su behind it, but has cleared from the Anchorage Bowl. Heavy
snow showers continue to impact the coast east of Prince William
Sound as well. The major player in the weather right now is the low
pressure system currently skirting past the eastern Aleutians and on
the door step of the Gulf of Alaska. It is reflected as a closed low
in the upper levels and as a mature occluded system at the surface.

There is also an upper level low in the Arctic, with troughing
extending down from the eastern north slope into Southwest AK. It
is this low that is feeding cold air into Southwest AK. In an
interesting turn of events, the low skirting past the eastern
Aleutians is aiding this cold air by drawing the trough south and
also enhancing wind speeds on the southwest coast and Aleutians.

&&

.MODEL DISCUSSION...

On the synoptic level models are in good agreement. The NAM
continues to have its own solution in resolving the low that moves
into the Gulf of Alaska later today. It starts out in step, but
then differences emerge tomorrow morning as the NAM places the
low center differently than other models. Fine scale differences
in models, mainly for Southcentral AK, will have impacts on the
forecast the next couple of days. Thus, we have high confidence in
the trend of active weather but low confidence for specific
weather features in the pattern.

&&

.AVIATION...
PANC...A brief break in the weather has allowed VFR conditions to
be present for the start of the 12Z TAF. However, the next weather
system is expected to move in this afternoon. It will bring more
snow, initially dropping category into MVFR conditions, then IFR
conditions overnight.

&&

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

A triple point low center forms near Kodiak Island today then
moves just south of the Kenai Peninsula this afternoon then slowly
weakens over the north Gulf through Thursday. The associated
occluded front approaching Kodiak Island this morning moves to
the north Gulf coast this evening and weakens. Expect gale to
storm force winds with and in advance of this system. Snow
spreading over Kodiak will shift to a mixture of rain and snow
through the morning hours then should transition back to snow late
this afternoon as the low moves east. Strong westerly winds will
spread across the island as the low passes to the east and will
give rise to blowing snow. Snow spreads north onto the Kenai
Peninsula and North Gulf Coast through today and inland into
Southcentral this afternoon. Generally light snow amounts are
expected inland with heaviest snow potential over the eastern
Kenai Peninsula. Strong winds coinciding with falling snow will
significantly reduce visibilities this afternoon for the Kenai
Peninsula.

Tonight and Thursday...
Winds and snow should diminish across the western Kenai
Peninsula late tonight so the blowing snow threat will end.
Strong outflow winds are expected across the eastern Kenai
Peninsula through Thursday so expect blowing snow to continue at
least into the afternoon hours. Light snow will continue inland
into the afternoon hours. Perhaps a little heavier over the
Copper River Basin depending on where the deformation band sets
up. Widespread westerly gales are expected over the western and
central Gulf with storm force winds over the Barren Islands.

&&

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

A Wind Chill Advisory remains in effect for the Kuskokwim Delta
through this early evening as a deep upper level trough persists
over the region. Wind chills of -50F are possible. Fair skies
will continue across much of the area through Thursday, with the
exception of a chance of snow today from Pilot Point eastward
through King Salmon and Iliamna as a large low pressure system
tracks south of the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A strong low south of the Aleutians continues to quickly track
eastward. Snow and blowing snow remain likely through mid-morning
over the eastern Aleutians and Alaska Peninsula. Relatively benign
conditions are expected across much of the Bering through the
remainder of the day. Two strong lows will develop south of the
Aleutians Thursday, bringing easterly gales and rain/snow to the
Chain, extending northward into the central Bering by Friday
morning.

&&

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

...Bering Sea and Aleutian Coastal Waters...

An active pattern is in store for the Aleutians coastal waters, with
multiple areas of low pressure affecting them. The first storm
stalls south of Amchitka on Friday, with another rapidly deepening
low tracking from well south of Cold Bay towards Kodiak Island.
These two storms act in concert to spread sustained gales across all
of the Aleutian chain and into the southern half of the Bering Sea.
Seas will be in the 15 to 20 feet range on the Bering Side and 20 to
25 feet on the Pacific side.

These winds and waves subside some for Saturday, before another
storm approaches the east central Aleutians from the Pacific,
while remaining well offshore. Northeasterly winds on the
backside of the low will spread sustain gales across all of the
Aleutian chain and the southern half of the Bering, with building to
near 20 feet across the southwestern Bering and west of Nikolski for
the Aleutians. Some sustain storm force winds may develop as well
for the east central Aleutians, depending on the track of the low
(how close to the coast does it get and how quickly does it deepen).

...Gulf of Alaska...

A trio of storms will move across the Gulf, with a storm on Friday
bringing widespread sustained gales to all of the Gulf, with perhaps
localized storm force winds as well. Seas of 15 to 20 feet may
develop for the outer waters. Then, a second storm moves in quickly
on its heels for Saturday, with sustain gales and a similar sea
state. A third storm again moves into the region, with high-end
sustained gales and perhaps sustained storms near the coast, with an
increasing sea state expected, perhaps in the 20 to 30 feet range
for the off shore waters and 15 to 20 feet closer to the coast.

&&

.LONG TERM FORECAST (Days 3 through 7)...
(Friday through Monday)

...Southcentral...

This looks to be possibly one of the most active patterns in many
years for the region, as the current model suite shows several
storms affecting the region in the extended period, and that's on
top of the first two moving through before it. These all will bring
multiple rounds of accumulating snowfall to all of Southcentral,
with some pretty impressive totals possible for some coastal
locations if the current model projections don't change (we all know
they usually do, as the further you go out in time, the more the
model variability increases).

An important feature to watch in later model runs is an unusually
strong mid-level polar low off the North Slope, that just sits
there while deepening to 477 dm. That in turn allows for a second
strong mid-level low on the order of 495 dm to take up residence
in the Bristol Bay region. These two systems then act in concert
to funnel very cold air from the Arctic into southwest Alaska,
with the Alaska Range keeping it just north and west of
Southcentral. This in turn allows for a third trough further south
in the north Pacific to feed off this funneling of colder air
aloft to help induce cyclogenesis (low pressure development), with
these storms intensifying as they track just along the baroclinic
zone aloft (just east of the trough axis), while the degree of
the cold air poised just north and west of the Alaska Range
prevents the storm track from moving further west or ingesting
warmer air from regions further south. This is because as the low
approaches, it does ingest colder air on the backside of each low,
as the air will be -30 deg. C at 850 mb (~4400 feet) across
southwest Alaska. This air modifies some, but stays cold enough to
allow any over-running precipitation to remain as snow.

So now on to the details. Our first storm (for the extended
period) moves from the north Pacific on Friday, to western Prince
William Sound Saturday morning. This storm will be in a deepening
phase, helping to draw abundant moisture northward.

Quickly on its heels is a second storm that moves from the
southwestern Gulf Saturday morning, to western Prince William Sound
by late Saturday evening, with more abundant moisture spreading
northward.

Then on Sunday, another fairly strong low moves from Kodiak
Island, to yep...you guessed it...western Prince William Sound
with a more pronounced precipitation shield ahead of it, due to a
stronger warm front aloft.

A fourth storm in a deepening phase will then track into the
Alaska Peninsula on Monday, with more over-running precipitation
moving into the region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 121 125 181 185
         Wind Chill Advisory: 155
         Flood Advisory: 145
MARINE...Storm Warning: 119 130-132 176
         Gale: 120 121 125 136-140 150 155 160 165 170-175
               177 178 180 351 352 411 413
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...PD

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
1054 AM AKST WED DEC 25 2019

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

0602 AM     SNOW             THOMPSON PASS           61.13N 145.72W
12/25/2019  E19.0 INCH       VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED 19 INCHES OF SNOW IN 24 HOURS
            AT THOMPSON PASS.

0549 AM     SNOW             9 ESE VALDEZ            61.07N 146.10W
12/25/2019  E10.0 INCH       VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED 10 INCHERS OF SNOW ALONG THE
            RICHARDSON HIGHWAY FROM EGAN DRIVE TO
            MILEPOST 12.

0300 AM     SNOW             WHITTIER                60.78N 148.73W
12/25/2019  E4.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED 4.0 INCHES OF SNOWFALL ALONG
            WHITTIER ACCESS ROAD FROM PORTAGE GLACIER
            ROAD TO CAMP ROAD.

0626 PM     SNOW             8 NW HOMER              59.68N 151.60W
12/24/2019  M3.0 INCH        KENAI PENINSULA    AK   CO-OP OBSERVER

0604 AM     SNOW             5 WSW CANTWELL          63.34N 149.08W
12/25/2019  E6.0 INCH        DENALI             AK   DEPT OF HIGHWAYS

            DOT REPORTED 6 INCHES OF SNOW ALONG THE
            PARKS HIGHWAY FROM MILEPOST 163 TO MILEPOST
            194.

0742 AM     SNOW             EAGLE RIVER             61.32N 149.55W
12/25/2019  E7.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 7 INCHES OF SNOW.

0642 AM     SNOW             TUDOR RD. AND PATTERSON 61.18N 149.75W
12/25/2019  E6.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER REPORTED 6 INCHES OF SNOW. SPOTTER
            WAS UNSURE ABOUT HOW LONG IT LASTED.

0300 AM     SNOW             GIRDWOOD                60.94N 149.18W
12/25/2019  E4.0 INCH        ANCHORAGE          AK   DEPT OF HIGHWAYS

            DOT REPORTED 4 INCHES OF SNOWFALL ALONG THE
            SEWARD HIGHWAY FROM INGRAHAM CREEK TO INDIAN
            ROAD.

1106 PM     SNOW             STROGANOFF DRIVE, ANCHO 61.12N 149.71W
12/24/2019  M6.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

0927 PM     SNOW             8 SSE ANCHORAGE         61.11N 149.82W
12/24/2019  M6.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            HUFFMAN RD/ELMORE RD.

0925 PM     SNOW             4 SE ANCHORAGE          61.16N 149.83W
12/24/2019  M7.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            LAKE OTIS PKWY/E 68TH AVE.

0922 PM     SNOW             5 SW ANCHORAGE          61.16N 149.98W
12/24/2019  M4.3 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            SAND LAKE RD./RASPBERRY RD.

0900 PM     SNOW             EAGLE RIVER             61.32N 149.54W
12/24/2019  M5.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            BARONOFF AVE/E EAGLE RIVER LOOP RD.

0649 PM     SNOW             8 SSE ANCHORAGE         61.11N 149.82W
12/24/2019  M4.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            HUFFMAN AND LAKE OTIS.

0640 PM     SNOW             7 SSE ANCHORAGE         61.11N 149.85W
12/24/2019  E4.5 INCH        ANCHORAGE          AK   PUBLIC

            SEWARD HWY/HUFFMAN RD.

0625 PM     SNOW             2 SE EAGLE RIVER        61.30N 149.53W
12/24/2019  M2.2 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            EAGLE RIVER RD./E EAGLE RIVER LOOP RD.

0622 PM     SNOW             4 SE ANCHORAGE          61.16N 149.83W
12/24/2019  M4.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            LAKE OTIS RD./E 68TH AVE.

0620 PM     SNOW             5 SW ANCHORAGE          61.16N 149.98W
12/24/2019  M3.0 INCH        ANCHORAGE          AK   OFFICIAL NWS OBS

            NWS ANCHORAGE - SAND LAKE RD./RASPBERRY RD.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1104 AM AKST WED DEC 25 2019

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

0918 AM     SNOW             PALMER                  61.62N 149.13W
12/25/2019  M3.3 INCH        MATANUSKA-SUSITNA  AK   COCORAHS

            COCORAHS REPORTED 3.3 INCHES OF NEW SNOW AND
            0.16 INCHES OF SNOW-WATER EQUIVALENT.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1118 AM AKST WED DEC 25 2019

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

0700 AM     SNOW             E. BARGE DR. TALKEETNA  62.23N 150.08W
12/25/2019  M5.4 INCH        MATANUSKA-SUSITNA  AK   COCORAHS

            COCORAHS REPORTED 5.4 INCHES OF SNOW WITH
            0.19 INCHES OF SNOW-WATER EQUIVALENT OFF OF
            E. BARGE DRIVE 7.6 MILES S OF TALKEETNA.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1157 AM AKST WED DEC 25 2019

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

1133 AM     SNOW             SUTTON                  61.71N 148.89W
12/25/2019  E4.3 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER REPORTED 4.25 INCHES OF SNOW
            OVERNIGHT IN SUTTON.

&&

MV