Brisk Wind Advisory 16, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
400 PM AKST Wed Jan 29 2020

.ANALYSIS AND UPPER LEVELS...
A 950s mb storm force low was located east of the Barren Islands
this afternoon with a weaker center just to the northeast. The
frontal trough associated with the storm center low was rotating
westward across Southcentral. Rain and snow was falling across the
north Gulf Coast with moderate snowfall over the eastern Kenai
Peninsula. Strong northeast winds through Thompson Pass caused
widespread low visibilities in blowing snow. Blizzard conditions
with heavy snow and frequent blowing snow ended over Kodiak Island
late this morning as the storm center shifted north. Strong cold
air advection off the Southwest Mainland continued snow and
blowing snow across with strong gap flows over much of the Alaska
Peninsula.

&&

.MODEL DISCUSSION...
Models overall are generally in good synoptic agreement. The main
focus will be mesoscale adjustments and bumping up winds through
gaps over the western Gulf and AK Pen and winds associated with
the next front moving across the Aleutians and Bering Sea on
Saturday.

&&

.AVIATION...
PANC...A brief period of LLWS is expected early this evening with
light north surface winds and southeast winds aloft. Surface winds
should shift to southeast and become gusty by late evening then
shift back to light north during the overnight hours tonight. VFR
conditions will likely prevail.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A strong low over the northwestern Gulf this afternoon will track
over the Kenai Peninsula and into Cook Inlet through tonight. As
the low moves over Cook Inlet and its front lifts across northern
Prince William Sound, the resultant increase in the pressure
gradient will orient to favor the development of strong
southeasterly gap winds through Turnagain Arm. Thus, a Blizzard
Warning remains in effect until 4 a.m. Thursday morning for
Whittier, Portage Valley, Turnagain Pass and eastern Turnagain
Arm. Expect additional snow amounts of 4 to 10 inches with locally
higher amounts and winds gusting as high as 45 to 60 mph. The
Turnagain Arm wind is expected to make a brief appearance across
the western Anchorage Bowl tonight. Gusty northeasterly winds will
also continue through this evening for portions of the Mat
Valley. For Palmer, however, the northeasterly wind is expected to
transition to a southeasterly Knik River Valley wind this evening
and linger through the overnight hours.

The Blizzard Warning for Kodiak has expired; however, locally
gusty winds and areas of blowing snow will persist over the next
couple of days. For Thompson Pass, snowfall and gusty winds should
also continue although blizzard conditions will wane as these
winds shift to the south and diminish in intensity. As winds and
precipitation make their way onshore, temperatures across the
Kenai Peninsula, Anchorage Bowl, and Mat-Su Valleys may climb a
couple more degrees this evening. We've seen highs across
Southcentral in the high 20s to low 30s with a high of 40 recorded
in Cordova. This shouldn't last long, however, as the winds taper
off later tonight. Temperatures will begin another cooling trend
as cold air wraps around the backside of the low. For Thursday,
snow showers will linger across the north Gulf coast as the rest
of Southcentral sees calmer winds and drier conditions.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Arctic high pressure remains in place, maintaining bitter cold
conditions with strong wind chills. A Wind Chill Advisory remains
in effect until Thursday morning for the Kuskokwim Delta and
Greater Bristol Bay areas. The coldest wind chills will continue
to be in the Kuskokwim Delta and Nushagak River valley. Along the
AKPEN and into the Alaska Range/foothills, light snow continues
and will spread north into the lower Kuskokwim Valley and west
into the Aleutian Range/foothills. Warm air advection with this
low will bring a brief reprieve from bitter cold in the Greater
Bristol Bay and middle Kuskokwim Valley areas. Precipitation will
diminish by Friday as a ridge builds over the Bering Sea.
Temperatures will return to the 20 to 30 below range, but surface
winds should be light enough that conditions won't reach wind
chill advisory criteria. Friday night into Saturday, a low
skirting south of the western Aleutians will swing a front
northeastward into the Bering Sea. This will initiate a broad
transition to onshore flow and cloudier, warmer conditions over
the Southwest Mainland. Temperatures may even break into the
positives for parts of the Kuskokwim Delta and Bristol Bay areas.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Upper level Arctic troughing persists over mainland Alaska, while
a ridge is building in over the western Bering Sea. Strong north
flow ahead of the ridge continues to bring enhanced gap winds and
cold air advection snow showers over the eastern Bering/Aleutians.
The trough will shift eastward and instability showers should
mostly diminish by Friday. A low in the northern Bering will steer
a cold front towards the western to central Aleutians,
maintaining widespread snow showers. But, with relatively lighter
winds do not expect significant impacts to visibility. A storm
force low will approach the western Aleutians from the western
Pacific Friday into Saturday. Winds will shift to westerly, then
southerly over the Aleutians. The low will have a moisture fetch
reaching nearly into the Tropics, bringing steady rain to the
Aleutians Saturday.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...
Gulf of Alaska: Strong northwesterly flow is expected to continue
for the Western Gulf through Saturday. This will create gale
force winds, especially through gaps and passes. Saturday night
into Sunday, this flow will diminish easing winds and seas. A
shift to southerly flow can be expected Sunday. We have a moderate
amount of confidence in the forecast. We are confident in
northwesterly flow and the pattern shift Sunday, but wind speed
may need to be adjusted a bit. Do expect gales to continue in the
Western Bering Saturday though.

Bering Sea: A low in the Western Aleutians Saturday will bring
strong gales and a few areas of storm forces winds to the area. It
will weaken as it moves east through Monday, allowing winds and
seas to calm to small craft advisory by Monday. There is moderate
confidence in this forecast. High confidence with low pressure in
the Bering, though wind speeds will likely need to be adjusted.

&&

.LONG TERM FORECAST (Days 3 through 7: Saturday through Wednesday)...
The upper level long wave trough currently over Alaska still
looks to shift east on Saturday. This will allow the ridge that is
currently over the Bering Sea and Aleutians to move east over
Southcentral AK. Over the weekend this high pressure will keep
cold air in place over Southcentral AK that will have moved in on
the backside of low pressure currently over Southcentral AK.
Meanwhile out in the Bering, a long wave trough will be digging
south with an anchoring low over the western Aleutians, meaning
unsettled weather in the Bering.

By early next week, movement of this high and continued
development of the long wave trough in the Bering will cause a
significant pattern shift for our forecast area. On Monday, the
axis of the high will move east to be located over Western Canada,
with low pressure over the central Bering. This will create stormy
conditions for the Bering and Southwest Alaska and broad southwest
flow over Southcentral, which should warm temperatures quite a
bit. Models are actually in good agreement for this pattern change
to occur. They have differences of exact location of the high and
low, but all are capturing the same general synoptic flow. This
gives us an above average confidence level in the long term, but
as usual figuring out specific weather systems will have to wait
until the forecast is in the short term.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 125.
 Blowing Snow Advisory 181.
 Wind Chill Advisory 155 161.
MARINE...Storm Warning 130.
 Gale Warning 119 131 132 138 150 155 165 170>172 180.
 Heavy Freezing Spray 130 132 138 150 155 165 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...BB