Brisk Wind Advisory 19, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
506 AM AKST Sun Feb 2 2020

.ANALYSIS AND UPPER LEVELS...

A strong storm is centered just southeast of Shemya and
encompasses an area over two thousand miles, from the southern tip
of the Kamchatka Peninsula to the Southwest coast. ASCAT winds
showed a swath of 50 kt winds across the western Bering during the
early morning hours with Shemya reporting persistent gusts to 55
mph throughout the night. The associated surface front which
pushed to the Southwest coast around midnight, is stretched along
a line from the eastern Alaska Peninsula to the Kuskokwim Delta
Coast. Light snow is developing along the boundary with reduced
visibilities less than one mile in blowing snow as winds are
steadily gusting between 30 to 40 mph along the coast. Across the
Bering from the Pribilof Islands south, light rain is developing in
narrow bands around the core of the low.

Temperatures are starting to modify warmer across the Southwest,
the Kenai Peninsula and Kodiak Island with Bethel. Colder
temperatures are still in place across the Susitna Valley, Copper
River Basin and northern Gulf coast. At four a.m. this morning
Cordova reported three degrees below zero with the valley
locations 20 to 30 degrees below zero.

&&

.MODEL DISCUSSION...

Models are in relatively good agreement on the synoptic pattern
through Tuesday, however there are significant mesoscale
differences by Monday. The updates made today were mainly focused
around winds and precipitation amounts with the first front moving
from the Southwest this morning to the rest of Southcentral
tonight.

&&

.AVIATION...
PANC...Low clouds developed early this morning and were added to
the TAF for several hours; however, there is low confidence on
exactly when ceilings will improve. A front across the Southwest
coast this morning will push to Anchorage during the afternoon.
Snow should be relatively brief as strong southeasterly flow
downslopes precipitation across the mountains. Wind shear may
be a problem this afternoon, but kept the mention out of the
package as there is still a bit of uncertainty between the models.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A shift in pattern will ensue today across Southcentral Alaska as
an occluded front spreads north and east across the Gulf. Snow and
strong winds will spread northward across Kodiak Island this
morning and up to the northern Gulf and eastern Kenai Peninsula
this afternoon and evening. Warm air with the front will cause
snow to change over to rain by this afternoon for Kodiak Island.
An advisory remains in place for the morning as there will be a
brief period of locally heavy snow and blowing snow as snow
initially moves in. An advisory also remains in place for the
eastern Kenai Peninsula for tonight as snow and blowing snow
combine to reduce visibilities. With low level easterly flow, the
heaviest snow will be east of the Seward Highway corridor, from
Whittier to Portage Valley. Snow will be lighter inland, but cold
temperatures will support dry snow which blows around quite
easily. Thus, even the movement of cars along the Seward Highway
will result in blowing snow and reduced visibilities.

West to southwest flow aloft will change the orientation of the
front from north- south to east- west tonight as it reaches the
northern Gulf. Thus, the above freezing air will not spread into
Southcentral. With arctic air and higher pressure out ahead of the
front, do expect a barrier jet to form along the north Gulf coast
tonight and strengthen through Monday morning. Have upped winds
to storm force in the latest forecast.

For the remainder of Southcentral, a weak negatively-tilted upper
level short-wave trough will pass overhead this afternoon through
tonight. However, strong low level southeasterly flow will develop
across the Kenai and Chugach Mountains, leading to downslope
drying from the western Kenai to Anchorage and the Matanuska
Valley, There could be a few flurries or brief period of light
snow right as it moves in today, but it wouldn't produce more than
a dusting. The Susitna Valley, on the other hand, will see more of
a southerly flow in the low levels, so do expect snow across most
of the valley this afternoon through tonight. Upslope flow will
lead to the highest amounts (several inches) over the northern to
western valley. Temperatures across Southcentral will steadily
increase as clouds and snow move into the region. This change in
pattern will bring an end to the prolonged cold snap of the past
month.

A low will move into the Gulf on Monday, though there is quite a
bit of uncertainty on where it will track. Nonetheless, expect the
front along the north Gulf coast to weaken and snow and winds to
diminish across Southcentral.

&&

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

The continental polar airmass that has had a prolonged grip on
southwest Alaska has begun to modify and retreat. At Bethel alone
the temperature has increased 43 degrees Fahrenheit from 12z
yesterday (-23F) to 20F at 12z this morning. There is a frontal
boundary moving into southwest Alaska and it has brought moisture
and warmer air advection. This morning the radars have been active
from Kipnuk to Pilot Point. Winter Weather Advisories were issued
for the Kuskokwim Delta along the coast and for Bristol Bay north
and west of King Salmon. As the front moves inland...the
relatively warmer air will work its way into the region. By
Monday morning the front will get sheared apart and undergo the
process of frontolysis.

&&

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

More unsettled weather expected this forecast period. Storm and
gale forces winds were detected overnight. There is a potent
surface low southwest of Adak this morning with an elongated
occlusion over the Bering. The models ping into a secondary low
developing later this evening west of the Pribilof Islands while
the actual triple point low develops south of the Akpen under the
jet stream. The tight pressure gradient will encompass the region
into Monday night and by Tuesday morning another low develops
near the Kuril Islands southwest of Attu Island.

&&

.MARINE (Days 3 through 5)...

Bering Sea/Aleutians: A weakening low will lift north from the
central Aleutians into the Bering Sea Tuesday into Wednesday,
leading broad cyclonic flow over the Bering with widespread areas
of small craft advisory level winds and possible embedded gales
through Wednesday. A strong low will approach from the western
Pacific Thursday, likely bringing gales and perhaps storm force
winds to the western Aleutians.

Gulf of Alaska: Swell-driven small craft advisory level seas will
continue, with no significant systems expected.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Unsettled weather and a cooling trend will be on tap Wednesday
into Thursday over the Southern Mainland as an upper low in the
Bering steers a cold front from west to east across the area.
Model uncertainty increases substantially Friday, given
disagreement over whether an Arctic trough dives down into
mainland Alaska, or dips farther west into Siberia, keeping all of
mainland Alaska in a south flow regime. This feature, and the
coincident strength of a North Pacific low Friday will determine
whether a warm, wet pattern comes into play Friday vs a very cold,
less wet pattern. In any case, most solutions converge and show
the cold air eroding Saturday. Meanwhile, wet unsettled weather
will continue over the Aleutians and Pribilofs in this progressive
pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisories 155 161 125 171.
MARINE...Heavy Freezing Spray Warning 119 130 139 185.
         Storm Warning 119 178 411 412.
         Gale Warning 120 130 131 132 136 137 138 139 150 160 174 180
                      181 185 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...MM