Brisk Wind Advisory 55, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Sun Mar 15 2020

The upper level ridge that has been over the forecast area is now
centered over the Gulf of Alaska and weakening over Southcentral.
An upper level low is over the eastern Bering Sea and Eastern
Aleutians pushing into this ridge which is increasing the
southerly flow approaching Southwest Alaska and Kodiak Island.
Farther west, there is a much larger upper level trough over the
Sea of Okhotsk which will edge eastward and become an important
feature for the Bering Sea later in the week.

&&

.MODEL DISCUSSION...
Models are doing well in the synoptic scale with the main
features lining up well across the spectrum of models. The biggest
challenge remains the system that will move from the Alaska
Peninsula on Monday night into the northern Gulf on Tuesday night.
The transition of this feature from a weakening elongated low near
the Ak Pen to a new triple-point low northeast of Kodiak is
handled a little different by each of the models and that is what
is bringing in the uncertainty to the forecast during that time
frame. The good news is that Tuesday through Wednesday actually
see better model agreement with the behavior of this system so
that will increase forecast confidence for Southcentral in
particular for those days.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

The upper level ridge will begin to shift eastward tonight, which
will allow cirrus to move into the region. Tonight will be
dry...and tomorrow will be dry. The models bring a storm into the
Anchorage Bowl Tuesday. The leading edge of the precipitation
shield will march up Cook Inlet. Expect a wintry mix. Some
locations in Southcentral will see all rain but Anchorage and the
Mat-Su Valleys will get a fresh blanket of snow on St Patrick's
Day.

&&

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

An Omega-Blocking pattern is currently set up across the North
Pacific with a 576Dm 500mb ridge extending northward across the
Gulf and into Southcentral. An 540Dm upper level low is currently
west of the ridge and is moving northeastward towards the central
Bering/Aleutians. The jetstream has slightly shifted southeastward
over the past 24 hours and now extends through the central and eastern
Bering/Aleutians into the Kuskokwim Delta. As the Omega-Block
continues to weaken this afternoon and evening, the storm track
will gradually shift eastward and allow for a weak low pressure
system to bring precipitation to the region. Precipitation will be
intermittent at the onset tonight through tomorrow morning and
become more steady late tomorrow afternoon. Due to a strong warm
air advection pattern as a result of a steady southerly flow,
precipitation type will begin as a rain/snow mix tonight and
change to rain tomorrow morning. There is the potential for
freezing rain in northern Bristol Bay tonight. Guidance shows
discrepancies in 850mb temperatures with the NAM/GEM being warmer
than the ECMWF/GFS. Due to the overall synoptic pattern and strong
southerly flow, the NAM/GEM is the preferred solution as that
pattern is more conducive to allow enough warm air into the region
to change snow to rain, especially along the coast. Temperatures
will be colder farther inland and in the higher elevations of the
Kilbuck, Ahklun and Kuskokwim Mountains and thus higher snow
accumulations are expected in those areas. A cold front will then
move from west to east across the area Tuesday afternoon as the
flow veers to northwesterly and 850mb temperatures rapidly fall.
Temperatures will be colder Tuesday night as 850mb temperatures
fall while a 500mb ridge builds in across the area to allow for
clearer skies. However, these cold temperatures will be short-
lived as the 850mb flow becomes out of the southwest Wednesday
morning and advects warmer air into the region. Wednesday will
also be dry as all of guidance suggests very dry mid levels as
700mb relative humidity levels remain less than 30 percent.

&&

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

An Omega-Blocking pattern is currently set up across the North
Pacific with a 576Dm 500mb ridge extending northward across the
Gulf and into Southcentral. An 540Dm upper level low is currently
west of the ridge and is moving northeastward towards the central
Bering/Aleutians. The jetstream has slightly shifted southeastward
over the past 24 hours and now extends through the central and eastern
Bering/Aleutians into the Kuskokwim Delta. A rain/snow mix has
developed across the central and eastern Aleutians ahead of a
1009mb surface low that is moving northeastward. Precipitation
type will change to all rain this evening and tonight across the
eastern Aleutians as strong warm air advection is occurring across
the area from a strong southerly synoptic flow. Precipitation will
be intermittent this evening and tonight, then become more steady
tomorrow morning. Precipitation is expected to develop over the
AKPEN tonight in the form of a rain/snow mix and change to rain
tomorrow morning. Winds will ease across the Aleutians tonight as
the pressure gradient across the area weakens. Strong gap winds
are likely early this evening across the eastern Aleutians due to
the localized funneling of winds. These gap winds will rapidly
ease later on this evening. A deep 966mb low over the southern
Kamchatka Peninsula is moving northeastward and weakening. This
low is expected to bring Small Craft Advisory winds to the parts
of the western Bering/Aleutians tonight and through tomorrow
morning. Large long period southwesterly swell will build into the
western Bering Monday night. A second deep 968mb low will take a
more eastward track and bring gale force winds to the western
Bering/Aleutians Tuesday morning through Wednesday night.

&&

.MARINE (Days 3 through 5 Wed through Fri)...

There is increasing confidence that a triple point low will form
near Kodiak Island Wednesday morning. Uncertainty remains with the
position of this low in the Gulf. If it skirts the north Gulf
coast as opposed to a more southerly track, gale force winds will
occur through channels including Shelikof Strait, the Barren
Islands and through gaps and passes on the Pacific side of the
Alaska Peninsula through Wednesday. Thursday morning, a front
associated with a low in the eastern Bering will enter the western
Gulf bringing with it small craft winds. There is low confidence
that another triple point low will form in the northern Gulf
Thursday night. If it does, expect gale force winds through the
same channels listed above through Friday.

Beginning Wednesday morning, a gale force front over the central
Aleutians will continue to push eastward across the Bering. As
the low center tracks northeastward, there is potential for storm
force winds on the backside of the low Wednesday over the
southwestern Bering. This low will track northward and exit the
Bering by Friday. There is moderate confidence that another front
will enter the western Bering sometime Friday. Depending on the
strength and track of this front, gale force winds will be
possible in the western Bering through Friday.

&&

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

Models continue to show good agreement that a triple point low
will form near Kodiak Island Wednesday morning. Upstream, an
upper level ridge quickly moves through Wednesday into Thursday,
ahead of a large Bering low that pushes a strong front eastward
across the Bering. This front will likely impact the southwest
coast midweek, bringing precipitation and strong southerly flow.
The track of this low still remains uncertain, though models are
showing the center departing the Bering to the north by Friday.
This will be followed by another upper level ridge moving across
the Bering and into southern Alaska through Sunday. Similar to
last week, warm temperatures and moist conditions will advect
into the Aleutians and Bering following the backside of the ridge.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 178 and 411.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...PS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
MARINE/LONG TERM...EZ