Brisk Wind Advisory 4, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
539 AM AKST Wed Jan 5 2022

.ANALYSIS AND UPPER LEVELS...

The pattern remains highly amplified as a Rex Block is currently
developing across the Bering/Aleutians. The broad upper level
ridge associated with the developing Rex Block currently extends
northwestward across the central and eastern Bering/Aleutians into
Siberia. A deep upper level trough extends across the Gulf of
Alaska and the Alaskan mainland. A strong 1056 mb surface high
extends across the North Slope while low pressure is located
across the eastern North Pacific. The strong surface pressure
gradient is responsible for the strong offshore winds across
Southcentral and Southwest Alaska. Radar shows minimal activity
across Southcentral and Southwest Alaska. Observations show strong
northerly to northeasterly winds across the areas.

&&

.MODEL DISCUSSION...

With the block of high pressure in place, the models are
struggling with the tracks of the surface lows coming out of the
North Pacific which is an issue for the Aleutians and Bering.
However, the models are consistent with the persistence of the
dry and cold temperatures over Southcentral into Friday.

&&

.AVIATION...

PANC...VFR conditions expected this TAF package. Winds will
remain northerly. Next chance for precipitation expected Saturday.

&&

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

Clear and very cold conditions will persist across much of the
Southcentral mainland through the end of the week. The exception
will be areas of clouds and patchy fog along the coast and
extending northward over the western Kenai Peninsula to the
Anchorage Bowl today as trough moves across the northern Gulf from
west to east. Gap winds are also continuing to wind down today,
with the strongest winds lingering through Thompson Pass.
Occasional gusts are still possible across the Matanuska Valley
this morning and around Valdez. Elsewhere, periods of snow and
easterly wind gusts continue for Kodiak Island as the
aforementioned trough moves toward the western Gulf.

A shortwave trough will drop south from the interior for THursday
morning. This will bring about a temporary shift in the mid-level
flow to a more northerly direction, allowing for an increase in
winds through Thompson Pass and across Valdez and Seward. A weak
surface trough will also develop across along the Southcentral
coast in the wake of the upper-level feature. Pressure falls
associated with this trough will also allow winds in Whittier and
Passage Canal to ramp up through the day Thursday.

A second, slightly more potent upper-level wave then drops south
late Thursday, helping to further amplify gap winds along the
coast and through mountain passes into Friday morning.

A third, and even stronger upper-level wave, then quickly moves
from the Chukchi Sea late Thursday to Southcentral Alaska Friday
morning. Colder air aloft will advect in behind this feature as it
stalls along the coast and elongates, running into a building
upper-level ridge from the western Gulf. The strongest cold air
advection will be from the Copper River Basin east to the Yukon
Territory. The concern with this feature is whether it will
initiate another bora event, similar to the New Year's event.
Right now, while it does appear that winds will increase as colder
air moves into the region, the upper-level set up - strength of
the upper-level wave, cold air advection, and associated jet
streak - are all not conducive to another strong wind event.
Especially given the building ridge to the south deflecting much
of the upper-level energy toward the west coast of the state.

By Saturday, an inverted trough south of Cordova will strengthen
as it moves west toward the Kenai Peninsula. As it does, snow will
overspread Prince William Sound and the eastern Kenai Peninsula.
A frontal system will also enter the western Gulf as its
associated surface low moves to the eastern Aleutians. The
combination of lower pressures near the AKPen and the arctic ridge
over the Yukon will act to tighten the pressure gradient,
allowing winds that were already on the increase late Friday in
the Matanuska Valley to continue through Saturday, with gusts
possibly reaching as high as 45 mph.

&&

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

Weak zonal upper and surface flow will continue to bring clear,
cool and dry conditions to the region. An upper trough will
descend from the north on Friday, slightly cooling temperatures
further. Easterly winds will also increase towards the end of the
weak as a front approaches the Aleutians, resulting in the
tightening of the pressure gradient over Southwest Alaska. No
precipitation is expected.

&&

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

A vertically stacked compact low is currently tracking near the
western Aleutians. South-southeasterly flow wrapping around it
extends eastward across the Chain and is bringing predominately
rain, although mixed precipitation remains possible through the
morning. Strongest easterly winds are expected between Atka and
Adak today and will diminish by early Thursday morning under the
low, before veering to a southerly direction behind it. Rain/snow
will also reach the Pribilofs by Thursday morning. After a brief
lull, another series of lows will approach from the North Pacific
by Friday, leading to intermittent rain across the Aleutians into
the weekend.

&&

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

Bering/Aleutians... Broad Arctic high pressure combines with an
elongated area of low pressure South of the Aleutians through
Sunday. Forecast confidence remains high. Easterly gale force
winds spread over the Aleutians and Bering through Sunday. Seas
building to 22 feet over the Western and Central Bering for
Saturday and Sunday. Increasing risks for freezing spray as winds
become more Northeasterly for Sunday.

Gulf of Alaska... A trough across the Northern Gulf yields to an
approaching low and front through Sunday. Forecast confidence
decreases with the low and frontal placement. Boundary jets
increase to gale force along the Gulf Coast Saturday. The low
spreads gale force winds over the Gulf with areas of storm force
along the North Gulf and Alaska Peninsula coasts, and lower Cook
Inlet through Shelikof Strait late Saturday into Sunday. Seas to
20 feet along the North Gulf Coast on Sunday.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...

A pattern change is expected during the extended period as the
Aleutian Low will deepen across the central North Pacific. There
is a high degree of ensemble agreement with respect to the
placement and intensity of synoptic scale features at both the
surface and in the upper levels. Moreover, there is a very low
degree of ensemble spread with respect to the position and
intensity of the Aleutian Low. The strengthening Aleutian Low will
allow for a greater chance of precipitation across Southcentral
Alaska due to the geostrophic wind component to be from the south-
southeast off the Gulf (onshore flow). However, the ageostrophic
component to the wind (pressure gradient driven) will be north-
northeast (offshore) due to high pressure over the Alaska Interior
and Yukon Territory while this Aleutian low deepens. This north-
northeasterly component to the wind will allow for the cold
temperatures to remain across Southcentral for the extended period
and increase the likelihood the predominant precipitation type is
snow. The best chance for precipitation across Southcentral will
be Saturday night through Sunday evening as a front moves across
the area. Forecast temperatures are expected to remain cold enough
for snow as the precipitation type across the Anchorage Bowl and
Matanuska Valley. The precipitation type forecast will be more
challenging across the lower lying coastal locations on the
windward side of the mountains due to warmer surface temperatures.
The highest precipitation amounts are expected to be across the
windward locations south of the Kenai and Chugach Mountains
(southern Kenai Peninsula and Prince William Sound).

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory: 131.
MARINE...Storm Warning: 173-176.
         Gale Warning: 127 128 130 132 138 150 155 165 170-172
                       178-180 352 411-414.
         Heavy Freezing Spray Warning: 119 121 126-128 138 139
                                       185 412 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...ED/KZ