Wind Chill Advisory 5, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
858 AM AKST Thu Dec 26 2019

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low over the eastern Kenai Peninsula is
currently bringing light snow to much of the western Kenai under
the associated deformation zone along its backside. A warm front
north of a second broad cyclonic circulation in the eastern Gulf
is leading to rain in the Cordova/Copper River Delta area, with
snow farther inland. This overall pattern is expected to persist
through Thursday.

While the deep upper trough axis has shifted eastward and surface
winds have diminished, very cold temperatures remain in place
over much of Southwest Alaska. Though no Wind Chill Advisory is in
effect, clear skies and light northerly winds will again bring
wind chills between -40 and -50 this morning to the Kuskokwim
Delta and Middle Kuskokwim Valley.

A brief lull is occurring over the central Bering/Aleutians under
an upper level ridge. A vertically stacked low near Kamchatka is
bringing strong easterly winds and rain/snow to the western
Aleutians. A number of low circulations developing in the North
Pacific will keep the pattern active into the weekend.

&&

.MODEL DISCUSSION...

As has been the case recently, models agree on the large scale
pattern with regards to a compact low center tracking
northeastward up the eastern Kenai Peninsula and moving near Prince
William Sound this evening. A broader, cyclonic circulation is
seen in the eastern Gulf with an associated warm front tracking
along the southern coast of the mainland. How all these features
interact will determine how far the rain will penetrate inland as
well as how much snow will occur north of the warm front and on
the backside of the aforementioned low. The most likely outcome at
this time is for a few inches this morning generally between
Girdwood/Thompson Pass and Whittier, slightly higher amounts in
the Valdez area and rain changing to snow farther south towards
Cordova.

&&

.AVIATION...

PANC...The forecast through Friday morning remains challenging.
Snow showers will occur in the Anchorage area through this
afternoon. Conditions will likely fluctuate between MVFR and IFR over
the next few hours as snow intensifies near the terminal. Snow
should taper off this afternoon, with VFR ceilings persisting as
skies clear overnight into Friday. As mentioned, confidence is not
particularly good and all flight categories could occur at least
for one observation period this morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An arctic trough will dig into Southcentral today and snow will
move back into Anchorage area and the Kenai as well as the Mat
Valley this morning. Snow will also become more widespread over
the Copper Basin. Therefore more accumulations will occur today
as the colder air filters in behind this arctic trough. Storm
force offshore winds through the Barren Islands will accompany
this, as well as strong and gusty gale force offshore winds
through favored gaps around Turnagain Arm, Portage Valley, and
Seward.

High pressure builds in Friday morning, and with widespread 850
hpa temps (temps at about 4000 feet) of -15 to -25C, expect
temperatures to be quite cold, with most inland locales dropping
below zero. High pressure will be short lived as another front
moves into the Gulf on Friday and to the north Gulf coast by
Friday night. This will bring accumulating snow to Kodiak island
and the Gulf coast beginning in the afternoon, and spreading over
the Copper River basin during the night. There is a chance of more
snow for the Cook Inlet area, but the bulk of the precipitation
will fall further east.

&&

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

Bone chilling temperatures expected across the region with lows
diving into the negative 30s in places like Aniak and Sleetmute.
Bethel will easily dip into the negative 20s and even some coastal
locations such as Kipnuk will be in the negative teens. An Arctic
low that is north of Deadhorse has a trough axis that bisects
southwest Alaska. With clear skies in place across much of the
region, radiational cooling will exacerbate the situation. Pilot
Point and Port Heiden which are on the Alaska Peninsula will be
the warmest locations both of which have cloud coverage and a
little extra distance from dome of continental polar air.

&&

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

Expect blustery conditions as a series of lows passes through the
region. Models struggle with the placement of the surface lows,
but all of the models show multiple fronts, unsettled weather and
gale-storm force winds at times. The latest ASCAT/Advanced
Scatterometer pass has already detected gales north and south of
the Aleutian chain as well as with the low near Kamchatka. And
ASCAT detected a few storms south of Adak just south of 50N. Any
breaks in the pattern will be short lived.

&&

.MARINE (Days 3 through 5)...
(Saturday through Monday)

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

A series of low pressure systems passes to the south of the
central Aleutians and Alaska Peninsula in the Saturday through
Monday time frame, with a separate disturbance dropping into the
Bering from the north. These features will bring sustained gales
to the entire region, with some storm force winds possible for the
southern Aleutian coastal waters, depending on the exact track of
the lows. This will only add to the freezing spray potential,
some of which will likely be heavy. Seas in the 20 to 25 feet
range will transition from west to east for the forecast period.

...Gulf of Alaska...

Sustained gales will overspread the Gulf and coastal waters on
Sunday, as another low pressure system lifts northeast from near
Kodiak to Prince William Sound. The winds may approach storm force
as well near the coast. These winds subside somewhat for Monday,
before increasing back to gales Monday night and Tuesday, as
another storm enters the region. Seas will generally be in the 10
to 15 feet range near the coast, and 20 to 25 feet further
offshore for most of the forecast period.

&&

.LONG TERM FORECAST (Days 3 through 7)...
(Saturday through Wednesday)

...Southcentral...

Not much has changed with our thinking compared to the previous
few days, as an active storm track looks to continue to affect the
region. Another storm system lifts north from the Pacific to Prince
William Sound on Saturday, bringing another round of snowfall to
most areas, with some locations along the immediate Gulf Coast
seeing rain).

Snowfall should decrease by Sunday, as the region will be
in between storms, before the next one arrives on Sunday night
into Monday. This system will bring more accumulating snowfall to
the region.

Then, another storm moves into the area for Monday night into
Tuesday. Where this storm goes is still very much in debate, as
the models differ on the strength and track. That said, the European
model (ECMWF) takes another strong low from near Kodiak Island into
the Cook Inlet, where as the American GFS model takes the low into
Bristol Bay, and the Canadian along the Alaska Range.
The general consensus over the past few days is for the further
southeast track, closer to the European solution. In any case,
another round of accumulating snowfall is likely, with perhaps
enough warm air moving in for some freezing rain concerns to
develop as well. Some precipitation may linger into Wednesday as
well as troughing persists.

...Southwest Alaska...

A storm system moving from near Kodiak Island to Prince William
sound will interact with a fairly robust trough dropping southwest
towards Bethel Saturday evening, bringing with it a reinforcing
shot of cold air. In fact, if this were to verify, it would be the
coldest air of the season as models project 850 mb (~5000 feet)
temperatures plummeting to -37 deg. C. This would translate to more
bitterly cold temperatures that could reach wind chill advisory
criteria. the accompanying northeasterly/offshore flow will also
keep the region dry.

Then for your Sunday evening through Wednesday time frame, a pair
of storms tracking closer (or through) southwest Alaska will bring
the potential for accumulating snowfall.

...Saint Matthew Island, Pribilof Islands, and Aleutians...

An active storm track near the Aleutians will promote periods of
snow with colder air continuing to funnel into the region from the
northeast. Further north, much colder air will move into the region
by Saturday evening, with decreasing temperatures and increasing
snow squall potential.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 125 Flood Advisory 145.
MARINE...Gale 150 155 160 165 170 171 172 173 174 178 179 180 181
411 412 413 414 119 120 121 125 136 137 138 139 351 352. Storm
175 176 177 130 131 132. Heavy Freezing Spray 130 139 140 160 179
180 181 185 414.

&&

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

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
952 AM AKST THU DEC 26 2019

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

0939 AM     SNOW             2 MILES ESE POTTER HILL 61.08N 149.78W
12/26/2019  E4.0 INCH        ANCHORAGE          AK   PUBLIC

            SPOTTER REPORTED 4 INCHES OF SNOW.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1217 PM AKST THU DEC 26 2019

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

1027 AM     SNOW             6 SSW GULKANA           62.17N 145.45W
12/26/2019  E3.0 INCH        VALDEZ-CORDOVA     AK   DEPT OF HIGHWAYS

            DOT REPORTED 3 INCHES OF SNOW ALONG THE
            RICHARDSON HIGHWAY FROM THE EDGERTON HIGHWAY
            TO MCCARTHY ROAD.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1220 PM AKST THU DEC 26 2019

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

1208 PM     SNOW             SUTTON                  61.72N 148.90W
12/26/2019  E1.5 INCH        MATANUSKA-SUSITNA  AK   TRAINED SPOTTER

            SPOTTER REPORTED 1.5 INCHES OF ADDITIONAL
            SNOWFALL TODAY.

&&

ED