Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 241923 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKST Tue Jan 24 2017

.ANALYSIS AND UPPER LEVELS...

The low pressure system that brought widespread blizzard and
blowing snow conditions to the Aleutian Islands and Southwest
Alaska continues to quickly fall apart over the Alaska Peninsula
this morning. A very potent warm front remains attached to this
low pressure system and is currently draped across the northern
Gulf of Alaska pushing toward the gulf coast. Temperatures across
the gulf coast have mostly warmed above freezing this morning as
warm air surges northward and this warm air should continue to
move inland throughout the day. Scatterometer data showed a 40 to
50 kt barrier jet set up south of Cordova overnight which has
diminished as the front weakened this morning. Southwest Alaska
continues to feel the the effects of the frontal occlusion as
scattered to numerous snow showers continue to be seen north of
King Salmon. Blowing snow has ceased across Southwest Alaska as
winds weaken, precipitation intensity diminishes and precipitation
type over Bristol Bay has changed over to rain.

A highly amplified upper level pattern is observed on water vapor
imagery this morning as an upper level trough extends from the
Bering Sea southward to 38N 156W. This amplified trough is the
reason for the change in weather pattern/temperature pattern as
warmer air from the subtropics is bringing warmer temperatures and
the increased moisture has led to some of the more recent snow
events across the state. The upper levels are actually quite
chaotic with numerous shortwave embedded within the longwave
pattern which will likely allow this amplified pattern to continue
for some time.

&&

.MODEL DISCUSSION...

Models remain in good agreement overall this morning. Numerical
guidance is having a rather difficult time resolving two areas of
low pressure over the Bering Sea through the short-term forecast
with the first being the low that brought strong wind and blizzard
conditions to the Bering Sea Sunday and Monday. This low is expected
to split with one moving into the Bering Sea north of Cold Bay and
the other moving into the North Pacific. Models aren`t exactly in
good agreement on the placement of the lows which slightly impacts
winds and seas over the southeastern Bering Sea.
Another discrepancy is another low pressure system skirting south
of the Aleutians through the week. This low likely gets stretched
out and has multiple low centers which are not resolved well by
models. This has only minor impacts in regards to the precip pattern
across the Aleutians. Models are actually in pretty good agreement
with snow changing to rain across Southcentral Alaska so far which
is encouraging for gathering rain/snow amounts for the forecast.
Overall a blend of the ECMWF and GFS was used for forecast package
updates this morning.

&&

.AVIATION...

PANC...VFR conditions should prevail through at least the first
half of the morning hours before scattered snow showers move
across the Anchorage Bowl. There is a good chance that between 18Z
and 00Z the airport could see several snow showers with minor
accumulations possible. Snowfall should clear by later afternoon
and a return to VFR conditions is expected.

&&

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

Snowfall and gusty winds associated with a coastal front continue
to diminish as the front pushes inland and falls apart this
morning. A second front will approach the north Gulf Coast
Wednesday and bring another shot of strong gusty winds and
precipitation to much of the region. It appears that Anchorage
will be mostly downsloped, with the bulk of the precipitation
falling along the eastern Kenai Peninsula. Strong gusts are
possible especially through eastern Turnagain arm late Wednesday
night into Thursday as an associated triple point low pushes over
northern Kodiak Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The remnants of the front that made landfall over Bristol Bay
yesterday morning has now spread northward into the Kuskokwim
Delta. Downsloping off the Kilbuck Mountains hasn`t developed as
strong as initially expected, and as a result snow accumulations
for the Bethel area were increased today. With continued gusty
offshore winds areas of blowing snow will continue, though
visibilities are expected to remain above one-half mile. The front
should dissipate outside of the area by this evening,
however cyclonic flow aloft will continue into Wednesday. This
will bring continued cloudy conditions and snow showers,
especially to western Bristol Bay and the Kuskokwim Delta. A
stronger low approaching Bristol Bay from the Gulf on Thursday
will then bring widespread accumulating snow back to the area for
the end of the work week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Widespread snow showers and northerly winds will continue over
much of the Western-Central Bering as low pressure sets up over
the Eastern Bering. The pressure gradient is relatively weak for
this pattern this time of year, so winds should generally remain
below gale force through mid-week. A weak low approaching the AK
pen on Wednesday afternoon will bring a chance of rain and snow,
but this system will be rapidly falling apart so anything should
that develops shouldn`t be widespread or significant.

&&

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

The main challenge for Wednesday night into Thursday will be the re-
enforcing warm front which moves from the gulf to the coast. There
is uncertainty on the track of the surface low that pulls the
front into the mainland. At this time, the low is expected to
cross from the Pacific to the eastern Bering. Precipitation along
the front over the gulf will be rain which is expected to spread
inland creating a mix of rain and snow or changing over to rain by
Thursday afternoon. The other big challenge will be wind with this
front. A tight pressure gradient along the front will bring gusty
conditions across the gulf and for much of the southern mainland
as the front moves inland. East to West oriented gaps will see
the strongest winds with this system.

The weather trend through the end of the week continues above
normal for temperatures and precipitation for the southern
mainland with a cooler trend remaining across the Bering as the
long wave trough remains centered over the Bering. The upper level
pattern should shift east this weekend and bring cooler
temperatures back to Southcentral as strong shortwaves move off
of the Kamchatka Peninsula forcing the upper low center closer to
the west coast. The weather pattern continues in an active regime
into the beginning of next week. Details in the extended forecast
will need to be monitored as models have multiple strong waves to
handle.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 119 120 131.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MC
SOUTHCENTRAL ALASKA...ELN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...KH



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