Gale Warning 298, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 PM AKDT Sat Mar 28 2020

.ANALYSIS AND UPPER LEVELS...

The pattern is generally dominated by a sharp trough moving
through Southern AK with a ridge building over the Bering Sea. In
the base of the trough is a surface low pressure center. This
feature has produced some light snow across parts of Southcentral
AK with heavier snow amounts and localized Blizzard conditions
across SW AK. There is some cold air pushing down the backside of
this feature as well, which will allow winds to intensify with a
sharp thermal gradient. The coldest air in the domain remains over
the Copper River Basin where temperatures dropped to about -10F in
certain locations earlier this morning.

Over the Bering, the building ridge is the dominant feature. It
is building over the Eastern Bering and helping to increase gap
winds through the Alaska Peninsula. Further to the west, a
decaying warm occlusion is pressing up against the Central
Aleutians. This is bringing some slightly warmer air, light rain,
and easterly winds.

&&

.MODEL DISCUSSION...
Models are in generally good agreement through Monday night.
There are minor discrepancies with the timing of the outflow wind
event in parts of Southcentral, but all models agree that it will
become gusty in many of the typical locations. Hi-res guidance and
hand edits were used to fine-tune that aspect of this forecast
package.

&&

.AVIATION...
PANC...Generally VFR conditions. Cold advection will increase
northerly winds across the airport complex tonight and Sunday.
Timing of the onset of the gusty conditions could vary by 1-2
hours either direction.

&&

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

The main story for Southcentral over the next few days will be
outflow winds along the northern Gulf coast. Winds will increase
tonight through the morning on Sunday, and will remain elevated in
most locations until Monday afternoon as an upper level trough
traverses through the area. Locations including Seward, Valdez,
and the Copper River Delta will see gusty northerly winds through
the rest of the weekend. A High Wind Warning has been issued for
Thompson Pass where northeasterly winds of 50-60 mph are expected
with gusts as high as 75 mph. In addition, locations including
Broad Pass and Palmer will see gusty northerly winds, with peak
winds occurring Sunday morning and diminishing by Monday
afternoon. Along with this northerly flow, colder air will arrive,
allowing for a return to single digit temperatures for the
beginning of the workweek.

&&

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

The low that tracked over the area is quickly moving across the
Gulf away from Southwest Alaska. Overall cloud cover is
diminishing, but some snow shower activity has developed with
daytime heating. These will diminish by sunset. Gusty northerly
winds impacting the area will gradually diminish through Sunday as
high pressure builds into the area. A front moving in from the
Bering will be rapidly weakening as it moves into the Kuskokwim
Delta coast Monday night. Thus, only some widely scattered snow
shower activity with no significant accumulations are expected. A
low develops along the front over the Alaska Peninsula on
Tuesday. The low will try to bring some snow mainly to coastal
Bristol Bay late Tuesday into Tuesday night, but there is quite a
bit of uncertainty as to how far north the snow gets into
Southwest Alaska.

With very quiet weather expected overall the next few days, the
primary weather story will be the temperatures, which will return
to single digits for most areas the next several nights. Highs
rebound nicely in the late March sun, with 20s expected in most
areas for the next several days.

&&

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

The primary weather hazard will come tonight into Sunday in the
form of heavy freezing spray across almost all of the Bering east
of the Pribilofs. A strong low pulling away over the Gulf with a
strong high over the northern Bering are causing strong winds to
pull a polar air mass southward across the region. The winds will
be enhanced as they move through the gaps in the Alaska Peninsula.
As such, heavy freezing spray is expected tonight along both sides
of the Alaska Peninsula. The threat diminishes on Sunday as the
winds weaken and daytime heating warms both water and air
temperatures. The area of high pressure shifts eastward into
mainland Alaska Monday as a front, currently over the far western
Bering, sweeps eastward, reaching Nunivak Island by Monday
evening. The front will weaken substantially once it passes the
Pribilofs as it shears apart. A low develops along the front on
the Pacific side of the eastern Aleutians, and will track along
the Alaska Peninsula through Tuesday evening. There is significant
uncertainty as to the track and strength of the low by Tuesday
evening, but most models agree it will be the next significant
chance of precipitation for the Alaska Peninsula during the day
Tuesday.

&&

.MARINE (Days 3 through 5/Sunday through Tuesday)...

Bering Sea/Aleutians: Confidence has increased since the last
forecast package with respect to the track of the low remaining
along the east coast of Russia on Monday. Widespread small craft
winds are expected in the western and central Bering with gale
force winds near the center of the low in the northwestern Bering.
The eastern Bering will see a minimal impact from this as this
low is expected to sharply track northeastward into the Chukchi
Sea. For Tuesday and Wednesday, forecast confidence remains low at
this time due to discrepancies between guidance with the
placement of synoptic features. Though, as of now no significant
low pressure systems are expected across the Bering or Aleutians.

Gulf of Alaska: For Monday and Tuesday there is a high confidence
that the weather will be relatively quiet as high pressure
extends across the area. The only area of concern is northerly gap
winds out of the bays and passes that will produce gale force
gusts at times on Monday. Uncertainty increases on Wednesday as
the next low approaches from the west. As of now it is marginal
that winds will reach small craft criteria.

&&

.LONG TERM FORECAST (Days 4 through 7/Monday through Friday)...

Guidance is consistent in the upper levels on Tuesday as an upper
level ridge builds over the Alaska mainland. This leads to above
average confidence in the temperature forecast with a warming
trend being expected. Confidence is much lower with respect to an
upper trough moving across the Bering/Aleutians on Tuesday and
approaching the Alaskan mainland on Wednesday as guidance differs
significantly in the strength and orientation of this trough. This
means that there is a high degree of uncertainty with respect to
the surface cold front associated with this trough and thus a high
uncertainty in the temperature and precipitation forecasts which
are dependent on the strength and movement of this feature.
Forecast confidence significantly lowers on Thursday and remains
very low for the rest of the forecast period as guidance shows
significant differences between solutions and thus the placement,
track and intensity of synoptic features remains uncertain at this
time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 131.
MARINE...Gale 127 155 185.
 Heavy Freezing Spray 119 126 127 140 150-165 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...ED