Small Craft Advisory 131, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 PM AKST Sat Feb 8 2020

.ANALYSIS AND UPPER LEVELS...

The main feature this morning continues to be the low pressure
system currently crossing the eastern Bering. Central pressure on
this system has weakened to 972 mb from last night, but hurricane
force winds are still blowing across the Alaska Peninsula and
Bristol Bay this morning. On the western side of this low, some
intense cold air advection is enhancing northerly winds and
causing a wide swath of blizzard conditions across the Kuskokwim
Delta and over the Pribilof Islands. The temperatures in the cold
air sector are currently hovering between -5 and -10F, but
earlier this morning were closer to -20F. With 40 to 50 mph winds
this was creating some impressive -50 to -60F wind chills. When
combined with the ongoing blizzard, this represents some very
dangerous winter conditions.

Meanwhile, further east, the surface front is very impressive and
obviously crossing just through the center of the Kuskokwim Delta,
with temperatures at Bethel and the surrounding areas jumping up
to around 30 degrees with southeast wind. This is also reflective
of the warmer temperatures across the Bristol Bay region this
morning.

Even further east, the warm front is crossing through Southcentral
Alaska this morning. Ahead of the front, southeasterly winds
brought downsloping conditions to the Anchorage bowl and
Matanuska Valley, causing a peak in temperatures this morning with
a peak in the southeast winds as well. Temperatures have remained
colder in the Susitna Valley, where snow is falling from Talkeetna
and northward and is reflected in a Snow Advisory for this area
today.

Numerous advisories and warnings have been issued across the
Southern Mainland and Bering/Aleutians covering various weather
hazards associated with this storm system. Please see the forecast
discussions and Watches/Warning/Advisory list further down this
page for specific details.

&&

.MODEL DISCUSSION...

Models continue to be in good agreement through the next 48 hours.
After that, timing and progression of the next system moving into
the Gulf of Alaska differs slightly. GFS is the slowest version,
with NAM and EC moving this system more quickly toward the
Panhandle. However, the difference for weather in the Anchorage
Forecast area is minimal, with some slight differences in wind
direction over the Gulf. Overall, the forecast confidence for the
rest of the weekend remains slightly higher than average.

&&

.AVIATION...

PANC...Winds over the airfield should decrease over the next
several hours as the front passes through and the wind direction
becomes more southerly. Winds aloft are expected to be more
southwesterly behind the front, so wind shear is expected to
continue for a while until the stronger southerly winds mix down
to the surface. Southwesterly flow is more conducive for showers
to move over the airport, and with air cooling aloft, snow will
become increasingly prevalent. Showers will be fairly widely
scattered in the Anchorage area, so if a shower does move over
the terminal expect it will be brief in nature.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
(Tonight through Monday night)

Plenty to talk about for much of Southcentral today. So far, the
airport peaked at 40 degrees late this morning as the Turnagain
wind made it into town, with some portions of the Anchorage Bowl
having made it into the mid 40s. This was quickly followed by a
heavy burst of snow, as the surface cold front crossing the region
was aided by one of a series of strong disturbances aloft passing
by, which maximized precipitation efficiency due to increased
ascent and accretion/aggregation (one of many processes where
snow flakes or supercooled water increase in hydrometeor size) in
the cloud bearing layer. This same scenario will also prolong
snowfall intensity for the northern Susitna Valley, aided by low-
level orographic lift. Here, the current advisory in place was
extended through Sunday evening.

Further east, a blizzard warning was hoisted on the fly as winds
at Thompson Pass were significantly higher than model guidance
earlier indicated. This is also likely an artifact of the stronger
disturbances described above helping to mix the winds down. These
winds should begin to taper off by Sunday morning, with snowfall
continuing.

Then on Sunday, a low will track from the southern Gulf towards
Yakutat. An inverted trough ahead of this feature should continue
to bring precipitation to the coastal locations from around
eastern portions of Prince william Sound towards the Canadian
border. Temperatures on Sunday will be similar to what was
observed today, before cooling Sunday night and Monday as colder
air aloft moves back into the region.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

A strong low centered near the western capes and its trailing
cold air mass will continue to be the focus over Southwest tonight
into Sunday. Expect another few inches of snow in the Bristol Bay
area tonight and in the middle/lower Kuskokwim Valley. Winter
Weather Advisories remain in effect. In addition the High Surf
Advisory remains in effect along the Bristol Bay coast. Along the
Kuskokwim Delta coast, the Blizzard Warning for today easily
verified. While snowfall is starting to taper off, bitter cold
return flow behind the low will cause temperatures to plummet
tonight over the Kuskokwim Delta. With winds still elevated,
hazardous wind chills will continue. In addition, winds will kick
up new snow and cause periods of significantly reduced visibilities.
Cold air will infiltrate the Bristol Bay area and Kuskokwim
Valley as well Sunday, with temperatures likely a good 10 to 20
degrees colder than today. Sunday night, lows will drop below
zero. The cold, dry pattern will persist into Monday, though
surface winds will diminish and switch around to northeasterly.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A strong low near the western capes will continue moving inland
tonight. Winds gusted to 84 mph in Cold Bay this morning, and have
been diminishing since then. Gales in Bristol Bay will diminish
tonight and heavy seas will subside. In the Pribilof Islands,
blizzard conditions have given way to slightly weaker winds and
lighter snow as the driving low progresses eastward. Behind the
low, expect a general reprieve from active weather over the
Bering, though northerly flow and Arctic air will maintain the
freezing spray concerns. In addition, areas of snow will continue
along the Aleutians tonight from cold air advection over the
Bering. A storm force low will approach the western Aleutians from
the southwest Sunday into Monday. Expect the leading front to
track across the Aleutians Sunday into Monday, bringing a swath of
southerly to southeasterly storms across the Aleutians and into
the Bering Monday. Expect several shortwaves to rotate around the
main low, maintaining a convective pattern behind the front.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

A storm force front moving across the Aleutians will diminish to
high end gales by Tuesday as it approaches the Eastern Aleutians.
Models currently disagree on whether a new low will develop along
this front in the Eastern Aleutians. If this happens, winds on the
west side will reach gale force on Thursday, but should not increase
any higher.

For the Gulf, Northwest gale force winds will continue through the
Barren Islands on Tuesday. A brief break will occur before the
next low moves northward into the Gulf. Expect gale force winds to
return late Tuesday into Wednesday and to continue into Thursday,
although the exact timing of the next low pressure system remains
uncertain.

&&

.LONG TERM FORECAST (Days 3 through 7: Tuesday through Saturday)...

The beginning of the long term has a brief break in the weather
for the mainland, with yet another frontal system slowly making
its way across the Aleutians. By Wednesday, a low develops along
the front associated with the Aleutian low, which then progresses
into the Gulf of Alaska. Timing and strength on this new system
remain somewhat in question, with forecast models having poor
run-to-run consistency in recent days. At the moment, it looks
like this system will track across the Gulf of Alaska, with much
of the mainland remaining under high pressure. If this track holds
true, the chances for snow over the next week are minimal for most
of the mainland, but outflow winds, particularly in Southcentral,
will be a concern beginning late Wednesday into Thursday. By the
end of the week, forecast models become quite inconsistent on the
placement of the parent low pressure system, with the GFS keeping
it in the Western Aleutians and continuing to develop new lows
south of the Aleutian Chain, while the EC moves the parent low
into the Bering and progresses the developing fronts across the
mainland. Current thinking is that the EC solution is slightly
more likely, because the GFS has had poor-run-to-run consistency
over the past week. Either way, the outlook for the marine areas
is stormy through the end of the week, with the forecast for the
mainland more uncertain.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 131 155.
         Winter Weather Advisory 145 152 161.
         High Surf Advisory 161.
MARINE...Storm Warning 150 155 160 165 175 176 177 178.
         Gale Warning 120 130 131 132 138 139 141
                      172 180.
         Heavy Freezing Spray Warning 150 160 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...LF