Small Craft Advisory 5, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
442 PM AKST Sun Jan 2 2022

.ANALYSIS AND UPPER LEVELS...

The bora wind event continues across Southcentral Alaska, with
widespread strong and gusty northerly winds along with bitterly
cold temperatures and wind chill readings. Some of the strongest
winds are being observed in the Matanuska Valley (where a High
Wind Warning is in effect), with persistent gusts of 75 to 85 mph
extending across Palmer and eastern portions of Wasilla. There
are reports of power outages, localized low visibilities in
blowing snow and minor damage as things get blown around.

The upper level pattern is slow to change, so conditions across
the region are mostly steady state. A high amplitude ridge is
parked over the central Bering Sea, with a corresponding trough
over the eastern mainland of Alaska down into the northeast
Pacific. A strong jet stream (at all levels) is oriented north-
south across western Alaska. A short-wave trough is dropping
southward down the Susitna Valley and Cook Inlet, beginning to
push westward into the side of the ridge. This is leading to a
new surge of cold air advection from the Alaska Interior to
Southwest Alaska. Meanwhile, to the west of the upper level
ridge, a warm front is strung across the western Aleutians
producing gale to storm force southeasterlies and rain.

&&

.MODEL DISCUSSION...

Models remain in very good agreement with the large scale pattern
evolution over the next three days. As a result, overall forecast
confidence is high. The primary challenge continues to be the
small scale details of the wind and temperature (and wind chill)
forecasts.

&&

.AVIATION...
PANC...Strong and gusty northerly winds will persist through
tonight. Upper level flow will become easterly and increase late
tonight through Monday morning. This should gradually push the
core of strongest northerlies off to the west, allowing winds to
diminish at the terminal.

&&

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

Low pressure south of the Gulf and high pressure over the Bering
continues to drive strong winds across the area due to cold arctic
air moving southward. The winds are expected to stay strong in
most areas through Monday afternoon and gradually relax by Tuesday
as the pressure gradient loosens up. High wind warnings are in
effect through Monday morning at 6 am for the MAT valley and
Anchorage area. Winds will continue to be gusty through Tuesday
morning across the Anchorage and MAT valley but should decrease
below warning levels. Dangerous wind chills are also likely with
wind chill advisories in effect for the Copper River Basin, the
Northern Susitna Valley and Thompson Pass. Other populated areas
will see wind chills in the -10 to -30 range.

Otherwise clear and cold conditions will continue across most of
the region with temperatures gradually dropping as winds decrease.
The only exception to this will be Kodiak Island where shortwaves
will move across the southern Gulf and bring chances of snow where
a few inches of snow are possible especially on Monday and Tuesday.

Heavy freezing spray will continue across parts of the area as
winds and cold air persist for the next couple of days.

&&

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

A blocking pattern with an elongated upper low over the Gulf and
a high amplitude ridge over the western Aleutians is persisting
with strong northerly flow aloft. Clear skies and cold, dry
conditions will continue across Southwest Alaska over the next few
days. The low will begin to retrograde westward, pinching off the
upper ridge and advecting the cold air mass and very high, gusty
winds towards Sand Point and King Cove areas of the Alaska
Peninsula through Monday morning. By late Monday, winds will shift
easterly and cloud cover will fill in along the Alaska Peninsula
and increasing chances for precipitation late Monday night through
midweek. Gusty northerly winds will continue through Monday
morning from the Middle Kuskokwim Valley through central Bristol
Bay. Wind chills below -40 will generally persist as well,
especially for the early morning hours and the advisories
remaining in effect for these areas. Although the winds are
expected to decrease Tuesday morning, there will be just enough
wind for the wind chill threat to continue, especially for the
Interior Bristol Bay.

&&

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

A blocking pattern with a high amplitude ridge over the Bering
Sea and a strong low to the east will persist for the next couple
days. Very strong northerly winds associated with a tight surface
pressure gradient and strong cold air advection, will persist
south of the Alaska Peninsula and retrograding westward towards
King Cove and Sand Point Monday morning. The westward progression
will continue Monday afternoon as the low begins to eat away at
the upper ridge. Winds will diminish and turn easterly allowing
clouds and precipitation to filter into the area Monday night and
stretch west through midweek. To the far west, rain will continue
this time and snow may mix in Tuesday.

&&

.MARINE (Days 3 through 5/Wednesday through Friday)...

Bering/Aleutians...

Forecast confidence remains above average during the 3-5 day
period. Widespread easterly gale force winds are expected across
the southern Bering Sea on Wednesday. These winds ease to below
gale force on Thursday and back northeasterly on Friday. There is
a high probability of heavy freezing spray across the ice free
waters on Friday. These winds will allow for large long period
swell to build in the western Bering Sea on Thursday due to the
long fetch over the water. This swell will then gradually abate on
Friday.

Gulf of Alaska...

Forecast confidence remains above average with widespread strong
easterly winds that are likely to reach gale force across the
southwestern Gulf. These winds will then weaken to below gale
force on Thursday and remain below gale force on Friday.

&&

.LONG TERM FORECAST (Days 4 through 7/Thursday through Sunday)...

The pattern will remain amplified during the extended period as
the Aleutian Low will deepen across the eastern Aleutians while
upper ridging extends across Siberia. This will allow for brisk
easterly winds across the Bering Sea to back northeasterly Friday
night. These strong northeasterly winds will allow for convective
snow showers across the Aleutians and is likely to result in heavy
freezing spray in the ice free waters. This pattern will also
allow for the cold temperatures to continue across Southcentral
and Southwest Alaska as offshore flow continues on Thursday and
Friday. Precipitation chances will increase this weekend,
especially for coastal areas along the northern Gulf as the flow
pattern will shift from offshore to onshore as the Aleutian Low
deepens. This will be an interesting pattern as pressure gradients
(ageostrophic flow) support an offshore surface wind flow pattern
across the leeward locations while the geostrophic flow will
favor an onshore surface wind flow across windward locations.
This will allow for precipitation across coastal areas such as the
southern Kenai Peninsula and Prince William Sound. There is a
chance for intermittent snow in the Anchorage Bowl Saturday
afternoon through Sunday afternoon as there is good model
agreement for weak cross barrier flow across the Chugach
Mountains. The weak cross barrier flow will allow for minimal
downsloping and thus increase the chance for precipitation.
Temperatures in the lower levels of the atmosphere will be
conducive to snow as the dominant precipitation type in the
Anchorage Bowl this weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 101, 111, 181.
         Blizzard Warning: 141.
         Wind Chill Advisory: 131, 141, 145, 152, 161.
MARINE...Hurricane Force Wind Warning: 150.
         Storm Warning: 127,130,131,132,155,177.
         Gale Warning: 119-125,128,136-140,351,352,160,165,170,
         172-176,178,180.
         Heavy Freezing Spray: 119-139,141,150-165,179-185
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...RC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...VR
MARINE/LONG TERM...ED