Gale Warning 108, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 PM AKST Sun Feb 10 2019

.ANALYSIS AND UPPER LEVELS...

A negatively tilted long wave trough extends from the northern
Bering into the southern Gulf of Alaska. Anchored at the base of
the trough is a vertically stacked low. This low can be seen in
visible satellite imagery as the textbook rotation in the southern
Gulf. Cold air is advecting behind the low over the western
mainland, AK-Pen and western Gulf. Behind the trough, a weak ridge
is building over the central Bering. A hurricane force,
vertically stacked Kamchatka low is skirting the western
Aleutians. This low has ample upper level support as it sits in
the left exit region of the jet where winds are approaching 162
kts. Strong cold air advection is occurring along the backside of
the Kamchatka low while warm, moist air is advecting in from the
North Pacific ahead of the system.

The warm and cold air advection in the Bering are associated with
warm and cold surface fronts, both extending from the surface
Kamchatka low. The warm front is pushing ahead of the low to the
northeast and covers much of the western Bering and central
Aleutians. The cold front extends from the low center to the
south into the North Pacific. A third front, positioned on the
backside of the long wave trough is draped over all of western
Alaska, the AKPEN and the southern Gulf. Stratiform precipitation
is falling in the area of this front which can be seen by radar
imagery. Ahead of the front, more convective style showers can be
observed in the northern Gulf and light winds are reported
throughout Southcentral.

&&

.MODEL DISCUSSION...

Models are synoptically in very good agreement. They are all
handling the placement and the overall strength of both of these
systems well. The main differences fall in the wind speeds with
both lows. The GFS/NAM solutions are proving to be more robust
bringing hurricane force winds to the central Bering on Monday.
The EC/Canadian are keeping winds just below hurricane force
during that time frame. While not near the speeds in the west,
the American models seem to be running a bit stronger than the
global models regarding winds surrounding the low in the Gulf.
The overall consistency persists through Tuesday.

&&

.AVIATION...
PANC...The fog was able to dissipate this morning due to
increased easterly winds not far above the surface that increased
the low level mixing. These winds diminish again by midnight and
that brings in the question of fog again later tonight. The
overall flow we are in is not typically conducive for fog, but the
ease at which it has been forming means that until there is a
bigger pattern shift it remains a possibility.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Sunday
night through Wednesday)...

Generally quiet weather will exist for the next few days in
Southcentral AK. Fog will be present again tonight around
Anchorage and the MatSu, though we do not anticipate it to get as
dense as last night and will be patchy in nature. This forecast
was based on persistence with fog occurring last night, but we
aren't going for fog a dense since a weak system will move through
overnight, mixing things up a bit. Enough stability will be present
in lower levels to allow for fog formation though. Another weak
disturbance moves through tomorrow night, but just some very light
snow is expected, with a dusting around Anchorage and perhaps an
inch in the MAT-SU Valleys. Otherwise all is quiet with high
pressure in place.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Saturday
night through Tuesday)...

Two lows will impact the southwest coast over the next three
days. The first low is currently moving through the Aleutian
Islands and will impact the southwest coast tonight into
tomorrow. This low is the weaker of the two lows. It is
anticipated to bring rain and/or snow depending on temperatures at
your specific location in southwest Alaska, so be sure to check
out your local forecast. Also expected are gale force winds,
mainly in coastal areas around Bristol Bay.

The second low is a much stronger low that will move through the
central Bering. Due to its large size and strength, it will have
multiple impacts on southwest Alaska. The first and likely most
significant impact will be sustained gale force winds along
coastal areas of Southwest Alaska. Before winds reach shore, a
front dropping fresh snow will (along with recently fallen snow
from the first low) will leave a loose snow pack to allow for
blowing snow to be an issue with these winds. As of now we are not
expecting visibility to reduce below a half mile due to warm
temperatures and and southerly winds, which have a tendency to not
produce intense blowing snow. However, this bears close watching.

The second issue also pertains to winds, which is coastal flooding.
A southwest south to southwest fetch of strong winds has the
potential to create a coastal flood issue for the Kuskokwim and
Delta and Bristol Bay. However, taking a look at today the current
thinking (after discussing with the ice forecaster) is that
shorefast ice will hold and protect the coast. This will mitigate
impacts in the Kuskokwim Delta, which will be the most exposed in
this wind direction. The Bristol Bay area will not see enough of
a fetch for long enough to be an issue. Therefore, not expecting
coastal flooding at this time. We will take another look though.

Lastly, freezing rain could be present as this system will be
sending warm air into Southwest Alaska. Looking at forecast
soundings and temperatures today, it does not favor freezing rain.
Therefore, backed off on the freezing rain forecast to a chance
but did not discount it completely based on one model run.

All in all, a busy few days of forecasting for southwest Alaska.

&&

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

The first of two low pressure systems for the Being Sea is
currently pushing through the central and eastern Aleutians. It is
still forecast to bring gale force winds the Aleutians and Eastern
Bering as it moves east tonight into tomorrow.

The more significant low is still anticipated to enter the
western Aleutians tomorrow night. Forecasts are still going for
this to be a deep and strong low, with a tight pressure gradient.
Therefore, were are still expecting storm force sustained winds
with hurricane force gusts for the western Aleutians and Bering
tomorrow night into Monday. Seas will be correspondingly high with
this low...with wave heights over 40 feet.

The low holds together well as it tracks northeast through the
Bering Monday into Tuesday, maintaining storm force strength over
the central Bering while sending strong gales into the Pribilofs.
The storm will largely exit our forecast area midday Tuesday.

&&

.MARINE (Days 3 through 5)...

The period begins early Wednesday with a low around 960 mb southwest
of the Bering Sea and another strong low south of Kodiak Island. The
track and intensity of both of these lows is not changing much from
run-to-run on the computer models and the overall solution looks very
reasonable, so the forecast confidence is above normal as
compared to other lows recently.

The low south of Kodiak should pull southeastward and bring in
some north-to-northwesterly storm force winds south of The Alaska
Peninsula and near Kodiak Island Wednesday then move out of the
area by Thursday. The low approaching the Bering Sea and the
front associated with it will bring periods of gales to most of
the Bering/Aleutian region with a significant area of storms in
the western Bering/Aleutians on Wednesday.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The long term forecast period starts early Wednesday with the
very active storm track over the western and northern Bering Sea
where it will generally remain through next weekend. A strong
frontal system will cross the west and central Aleutians on
Wednesday and then continue across the Bering Wednesday night and
Thursday to reach the Southwest Alaska coast Thursday afternoon.
This front will then shear apart and dissipate Thursday night as
it tries to swing inland to be replaced by a high amplitude ridge.
The next strong front will move into the central Bering Thursday
night and continue east to push across Southwest Alaska Friday
night. Another frontal wave will follow behind it, crossing the
Alaska Peninsula Saturday and then lifting northeast into Southern
Alaska Saturday night through Sunday. Yet another strong front
will approach the western Aleutians late Saturday night. Its
powerful parent low will track into and across the Bering Sunday
through Sunday night with its associated frontal system swinging
east across the Aleutians and Alaska Peninsula to reach Southwest
Alaska Monday.

For Southcentral Alaska, the long term forecast period will begin
with a low track from west to east across the southern Gulf
Wednesday with a cold upper level trough to the north digging
into Southcentral Alaska behind it. The result will be a rapid
strengthening of offshore flow Wednesday afternoon through
Wednesday night, particularly through channeled terrain gaps.
Upper level ridging will build in from the west Thursday and
Friday bringing a gradual easing of the offshore flow and steady
warming aloft. By Friday night the axis off the upper level ridge
will push east to be centered over Southcentral Alaska with a
weakening frontal system following behind on Saturday. A second,
better organized frontal wave will push into Southcentral Alaska
Saturday night and Sunday. Ridging will briefly rebuild Sunday
night ahead of another front coming in from the southwest.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 191 195. Winter Weather Advisory 155.
MARINE...Hurricane force winds 177 178. Storms 132 175 179 181 185
411-414. Gales 130 131 138 150 165 170 172 173 174 176 180 352.

&&

SYNOPSIS AND MODEL DISCUSSION...RA
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KVP/KO
MARINE/LONG TERM...JR

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1119 PM AKST Sun Feb 10 2019

AKZ155-112030-
Kuskokwim Delta-
Including the cities of Bethel, Hooper Bay, and Nunivak Island
1119 PM AKST Sun Feb 10 2019

...Coastal Storm to bring elevated water levels and strong onshore
winds to the Kuskokwim Coast from Hooper Bay to the Kuskokwim
Bay through Tuesday morning...

A strong low in the Bering Sea will bring elevated water levels
through Tuesday afternoon to coastal areas. Water may push through
fissures and openings in ice and along shorelines. Residents
should use cause caution if venturing near or onto ice.