Gale Warning 215, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 AM AKDT Thu Mar 21 2019

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a high amplitude ridge across
Western Canada and into the Alaskan Interior. There is a closed
low south of the AKPEN and another closed low near the western
Aleutians. Between the ridge and the low south of the AKPEN there
are multiple embedded disturbances across Southcentral Alaska.
A warm front tracking northwest will continue to march into
Southwest Alaska where it will meet up with an Arctic airmass.
There is a jet core north of Deadhorse and a second jet core south
of the Kamchatka peninsula. Temperatures continue to run above
normal in multiple regions of the state. Yesterday, the high at
Cordova was 61F and there were numerous locations in SE Alaska
that were in the 60s.

&&

.MODEL DISCUSSION...
The GFS and the ECMWF initialized well with the placement of the
surface low south of the AKPEN when compared to the
ASCAT/Advanced scatterometer data. The global models are in good
agreement with the synoptic scale features through 00z Saturday.
This is seconded by the tight grouping of the GFS ensemble members
with the high over Siberia and the main low south of the AKPEN.
There are some differences with the timing of the precipitation
shield and the p-type over SW AK. The model of choice for the
short term package was the GFS.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Low level wind
shear possible from 12z-16z today.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Temperatures over the area will continue to be well above normal
over the next couple of days with southeast flow aloft and rather
high 500 mb heights. The low centered well south of Kodiak
Island will slowly move north today. The low will then move
northeast on on Friday, crossing the upper Alaska Peninsula early
Friday afternoon. A front associated with this low that is
currently over the southern Gulf and Kodiak Island will reach the
Kenai Peninsula this afternoon, with increasing rain and winds.
The front will reach the north Gulf coast and Prince William Sound
tonight, with Gale force winds expected. The front will stall and
weaken on Friday. On Friday night, the front will begin to push
ever so slightly back towards the southwest as the parent low
slides westward in Bristol Bay, and the strong northwest Canada
ridge nudges into eastern Alaska. By late Friday night the winds
over the northern Gulf will be quite weak, but moisture and
precipitation will continue over the Kenai Peninsula and north
Gulf coastal areas.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Thu and Fri)...
An active pattern remains across the area. Several weak warm
occlusions are swinging through Southwest AK courtesy of a well
wrapped surface low south of Kodiak. Each of these is bringing a
healthy band of precipitation and an additional push of warm air.
But that warm air has been slow to make it into the northern
portion of the YK-Delta thanks to north to northeast surface winds
reinforcing some colder air. Thus, we have opted to upgrade the
Winter Weather Advisory for the Delta to a Blizzard Warning for
the coast from Toksook Bay north. Conditions are likely at their
worst right now and should slowly improve this morning as winds
start to diminish and warm air continues to try to erode the cold
dome. The cold air across the interior Delta and the Lower
Kuskokwim River Valley will create the potential for some freezing
rain and mixed precipitation early today as warm air nudges in
aloft. The Bethel 12z upper air sounding shows this warm air
moving in quite well.

As the surface low moves towards the Alaska Peninsula on Fri,
expect gusty southeast winds to envelop all of Southwest AK. These
winds will be enough to push temperatures above freezing at most
(if not all) locations. The warmest spots will be on the northwest
side of any terrain where some localized downslope winds should
add a few more degrees. These temperatures should also allow all
precipitation to turn safely to rain.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Thu and
Fri)...
After an extraordinarily quiet weather pattern for the Bering,
things are about to become a lot more active. Right now, cold air
showers and modest winds will start the day. However, two
distinct features will bring the marked change to the pattern. The
simpler of those is a mid 960's mb low that will track towards
the Western Bering by late Fri night. This system will arrive as
an impressive warm front blasting through the Western Aleutian
late Fri. Precipitation will start as snow with increasing
southeast winds. As the front passes through, winds will quickly
shift out of the southwest and turn precipitation over to rain.
This front will bring some high-end gale force winds back into the
Bering Sea.

The more complex piece will be the interaction of the cold air in
place with a low moving up from the North Pacific. As these two
features collide, a potent deformation axis will form across the
Central Bering. This axis will represent a sharp dividing line
between warm air, rain, and southeast winds versus cold air, snow,
and northwest winds. Exactly where this feature sets up will be
key and is still somewhat uncertain. A Winter Storm Watch has been
issued for the Pribilof Islands for tonight into Friday as St
Paul and St George look to be right on the eastern edge of the
cold air. The snow and blowing snow will also push down into Dutch
Harbor initially. The north side of the Eastern Aleutians into
the Alaska Peninsula can also expect a very showery pattern, but
they look to stay mostly rain in the warm sector.

&&

.MARINE (Days 3 through 5/Saturday through Monday)...
For the Gulf of Alaska...southeast flow creating small craft to
gale force winds and elevated seas will continue into Saturday.
Winds should taper off pretty quick on Saturday. Models have a
tendency to calm winds a bit quickly, so we will watch the
forecast for winds and waves in the area. We have accounted for
this model bias in the forecast so we are confident in it, but
bears watching none the less. After Saturday, a brief break in the
weather is expected.

For the Bering Sea...Strong northerly flow is expected to continue
into Saturday, then gradually weaken to below small craft advisory
by the end of the day. A pattern shift is then expected to occur
Sunday with the first of a couple low pressure systems entering
the western Bering. This will switch winds to a southerly direction
and elevate winds speeds again. We are confident in the pattern
shift and elevated winds speeds, but the placement of the low and
strength of winds will need to be honed more in coming days.

&&

.LONG TERM FORECAST (Days 3 through 7/Saturday through Wednesday)...
The long term will start with the current pattern remaining in
place for southcentral AK and low pressure in the western Bering
Sea. Lows will continue to train north into southcentral AK until
Sunday. Conditions will vary slightly with the passage of each
low, but the common thread between them is that warm, wet and
windy conditions will continue for Southcentral through the
weekend. Early next week it looks promising for a break in the
weather. Models are coming into agreement that high pressure will
arrive over the Gulf of Alaska and Southcentral, finally breaking
the trend of low pressure systems. While models still differ on
placement of the high pressure ridge, more of them are coming into
agreement. So, we have increasing confidence that a pattern shift
to calm weather will occur.

Out in the Bering Sea, a series of lows will move through the
western and central Bering during the long term. A weaker low will
start the long term, followed by a strong and well organized low
moving north through the Bering Monday into Tuesday. A frontal
system from this low could work its way into southwest Alaska. As
with Southcentral AK, there are differences in the long range
models with the weather in the Bering. However, they do agree a
strong low will move through, so we have confidence in this
pattern. It's just a question of how strong and exactly where the
low center will be located. This of course will affect the
forecast, so we will have to hone the details in the coming days.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 155.
 Winter Storm Watch (Blizzard) 195.
MARINE...Gale Warning 119 120 125 130>132 136>139 150 170>174 176
                179 181 185.
 Heavy Freezing Spray 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
MARINE/LONG TERM...BB