Gale Warning 105, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKST Fri Feb 8 2019

.ANALYSIS AND UPPER LEVELS...

Pattern amplification since yesterday transformed into an omega
block across the eastern North Pacific which extends northward
across the Gulf of Alaska and over the Alcan border. Water Vapor
Satellite imagery shows this classic signature with the low
pressure centers spinning along 40N. Abundant moisture is
streaming along the periphery of the ridge which is currently
centered just south of the Gulf. Across the Bering...a strong
storm system is moving toward the western waters with the surface
front draped across the western Aleutians. Precipitation started
as snow, but quickly changed over to rain early this morning. One
last mention for the Southwest mainland...the front along the
Kuskokwim Delta is picking up eastward momentum and pushed just
east of Bethel bringing rain to Aniak and the Kuskokwim Mountains.

&&

.MODEL DISCUSSION...
Models are in good general agreement with the overall synoptic
pattern through Saturday then diverge on how quickly to break down
the ridge on Saturday. Overall only minor changes were made
through Sunday, mainly because there is good agreement initially
and where models begin to differ confidence lacks due to great
differences between surface lows. The GFS was the primary choice
for updates as it was the middle ground solution. The driver in
the upcoming synoptic change will be the strong storm system
moving to the Bering today which swings a significant short wave
across the eastern Bering and Southwest mainland Saturday night
and then to Southcentral and Gulf for Sunday.

&&

.AVIATION...
PANC...VFR conditions are expected through Saturday morning along
with light winds.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level ridge will remain over the area into Saturday,
with the ridge axis near the Canadian Border. This ridge is quite
"dirty" with considerable cloud cover over the area. Successive
systems will slowly begin to erode the ridge from the west, with
some precipitation possible over the Kenai Peninsula and Susitna
valley. Precipitation chances will begin to spread further east
Saturday afternoon as a weak short- wave trough "tops" the ridge.
A much stronger system will push in from the west beginning late
Saturday night. At this time, it looks like precipitation will be
in the form of snow from Anchorage northward. However, there is a
chance that some rain could mix in if a nose of warm air pushes
further north than currently forecast.

&&

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

Bands of light snow will continue to fall today from Bethel east
to Sleetmute as colder air advects in behind a frontal system.
South of the front, a moist, southerly flow will continue to
produce mainly rain from the AKPEN and Bristol Bay region
northeast across the southern reaches of the southwest as a strong
low- level jet pushes warmer air in from the south. As this
system weakens tonight, a second wave will travel north along it.
Much like the previous system this wave will usher in another
round of warmer air as the flow once again becomes southerly.
Precipitation over the AKPEN later today will lift north with the
system, overspreading Bristol Bay tonight producing mainly rain.
Snow during the onset for areas north of Bristol Bay will quickly
change to rain tomorrow. A few isolated areas along the lee side
of the Kilbucks and in the far interior southwest where
temperatures will drop at or below freezing behind the first
front, may see a very brief period of mixed precipitation and/or
freezing rain before the warm air scours out the colder air
trapped at the surface.

This second wave will then be kicked east late Saturday as an
occluded front races across the Bering toward the coast. Rain will
again change back to snow as the front tracks east and colder air
funnels in on westerly winds. A trailing upper-level shortwave
will likely keeps clouds and scattered snow showers over the
region through early Sunday. Colder and drier conditions will
then settle in late Sunday as a ridge builds in from the west.

&&

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

A weakening frontal system will bring a few scattered showers for
the central ALeutians this morning. The bigger story, however, is
the rapidly deepening hurricane-force low tracking west of Shemya
today. This system will bring a swath of southerly storm-force
winds across the western Aleutians and Bering this morning as its
occluded front lifts north. Behind the front, the combination of
a tightening pressure gradient and cold air advection wrapping
around the back side of the low will produce hurricane-force winds
with gusts as high as 90 mph for the open waters of the western
Bering as well as areas including Shemya and Attu. This low
quickly lifts north tonight with westerly gales in its wake as the
occluded front moves east toward the Alaska coast. Warmer air in
advance of this system will bring rain to the Bering and Pribilofs
with areas of scattered snow showers behind it as the colder air
works east. A second strong surface low then moves toward the
western and central Aleutians late Sunday with another round of
rain and southerly storm-force winds.

&&

.MARINE (Days 3 through 5)...

Light winds and calm seas are expected across the western
Aleutians Sunday morning under a ridge. Marginal northwesterly
gales will remain possible west and north of the Pribilofs Sunday
morning associated with a weakening low over Siberia, though
winds are expected to diminish through the day as the
aforementioned ridge tracks to the east. Winds will rapidly
increase to southwesterly gales and seas will build across the
western Aleutians Sunday evening, further increasing to storm
force by Monday as a strong ~960mb low tracks to the west of Attu.
Winds will gradually diminish Tuesday as the low departs to the
north. Model agreement is very good for the above events.

Model agreement is in better consensus today for possible
northwesterly gales and higher seas over the western Gulf of
Alaska and the Barren Islands beginning Sunday afternoon and
continuing into Monday morning as a trough tracks over Bristol Bay.
Winds will diminish and seas subside Monday afternoon as a ridge
builds in from the west. Generally light winds and calm seas will
continue Tuesday under the ridge.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning Sunday, a high amplitude ridge over eastern Alaska will
continue to drift east over the ALCAN border as a deep upper low
and associated strong frontal system pushes east across the
southern mainland. The cold front will be racing across the
mainland Sunday morning bringing rain initially then likely changing
over to snow as cold air rapidly moves in behind the front. There
is still some uncertainty regarding how well the front maintains
its structure as it crosses into Southcentral Sunday afternoon but
good enough model agreement to include accumulating snowfall in
the forecast for populated areas in Southcentral.

Ridging builds in behind the departing system Sunday night into
Monday dropping temperatures to near or below normal values across
the mainland. The very active pattern continues over the Bering
as a barrage of strong North Pacific lows are expected to blast
across the area, with the GFS and EC showing another 2-3 storm
force lows making the same north/northeasterly track across the
Western Bering, separated by 2 to 3 days. There is uncertainty as
to how far east and how much the associated frontal systems hold
together as they push into Southcentral, but there is confidence
that the east Pacific ridge will re-build over the eastern half of
the mainland in between systems.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind warning 191.
         Flood Advisory 155.
MARINE...Hurricane Force 178 411.
         Storms 177 185 412 413.
         Gales 173 175 176 179 181 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...KVP

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
213 PM AKST Fri Feb 8 2019

AKZ155-092315-
Kuskokwim Delta-
Including the cities of Bethel, Hooper Bay, and Nunivak Island
213 PM AKST Fri Feb 8 2019

...LOCALIZED FLOODING WILL CONTINUE OVER THE NEXT FEW DAYS FOR THE
LOWER KUSKOKWIM DELTA...

A mixed bag of weather is in store for the Bethel area over the
weekend and into the next few days. High temperatures will be in
the upper 30’s with lows dipping down to into the 20’s
overnight. Another round of mostly rain mixing with some snow is
forecast for Saturday night.

Temperatures fluctuating around freezing and mixed precipitation
will cause difficult commuting conditions. Also, recent rainfall
has caused ponding of water on roadways and in low lying areas.
This flooding is expected to continue. If you have belongings
surrounded by water you may want to move them before they become
frozen when temperatures drop Sunday night.