Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 171903 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
1003 AM AKST Mon Feb 17 2020

.ANALYSIS AND UPPER LEVELS...

A 966 mb low centered north of Dutch Harbor is in the process of
strengthening as it lifts northward. An associated frontal band is
bringing precipitation and gusty southerly flow to the Alaska
Peninsula and Southwest coast, with blizzard conditions over
Nunivak Island and the northern Kuskokwim Delta coast. A second
low centered west of Adak is bringing gusty northerly winds to the
western Aleutians as it moves toward the southeast.

Meanwhile over Southcentral, a warm front is lifting inland,
spreading in light precipitation that has worked its way from the
Kenai Peninsula northward into the Susitna and Matanuska Valleys.
Light northerly flow at the surface combined with mid-level
southeasterly flow has kept most of the area dry and downsloped,
allowing for mostly trace accumulations overnight.

&&

.MODEL DISCUSSION...

Overall, model solutions are in good agreement with synoptic
features through Monday night. By Tuesday, solutions diverge with
the placement of a northbound low in the Gulf of Alaska. The 6Z
GFS solution shows a stronger and more concentric low lifting over
Southcentral for Tuesday night while the other models show a
weaker low approaching Prince William Sound. Forecast confidence
still remains low for Tuesday onward. A GFS/EC solution was
preferred for the morning forecast package.

&&

.AVIATION...
PANC...A front lifting over Southcentral will bring MVFR
conditions with light snow to the terminal early this morning.
Conditions are expected to improve to VFR by late morning but
LLWS will develop as winds increase aloft.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Mon and
Tue)...
The active weather pattern is upon us. The first in a series of
systems is currently sliding up from the Kenai Peninsula through
the Susitna Valley and into the Northern Gulf Coast. This is the
weakest of the 3 systems that will move through the area over the
next couple of days. With antecedent cold air, light snow will
continue to fall through portions of the Kenai Peninsula over
towards Valdez and up through Talkeetna this morning. This snow
is coupling with some stronger winds in the Portage Valley and
Turnagain Arm to reduced visibilities at times as well.

A strong low will deepen over the Eastern Bering Sea through the
day today. This will drive a stronger front towards the area. This
front will increase the gusty winds in places like the Matanuska
Valley and the Turnagain Arm/higher elevations of the Anchorage
Hillside through the day. A High Wind Warning has been hoisted for
the Turnagain Arm/higher elevations of Anchorage in response to
this. The other aspects of this front are some low-level warm air
and deep, moist southerly flow. These attributes continue to make
for a very complex forecast. The winds will bring warmer air to
many places such as the Anchorage Bowl, the Mat Valley, and most
of the coastal sites. These winds should also aid in keeping the
Anchorage Bowl and the Mat Valley mostly downsloped (dry)
initially. So even as temperatures could spike into the mid 30s or
low 40s, precipitation should remain light. The opposite will be
true in the Susitna Valley and other cold interior (and higher
elevation) locations that do not see as much wind. These
locations will likely see several inches of accumulation today
through this evening. The higher elevations of the Anchorage
Hillside could see the rare combination of snow and strong winds
creating localized reduced visibilities in blowing snow.

By tonight and into early Tue, the final piece of the storm will
start to move in. The upper level low from the Bering will usher
in a broad cold air mass. This will collide with moisture
streaming from south to north over the Gulf Coast. The net effect
will be widespread accumulating snow from the Susitna Valley over
to Thompson Pass. Some of this snow could be moderate to heavy at
times. Several winter weather products remain in effect to address
these concerns. For the Anchorage Bowl and the Mat Valley the key
will be the temperatures. If the winds die off early enough, the
colder air should turn precipitation to all snow during the day
Tue. This would lead to an impressive snow set-up, especially for
the Anchorage Hillside. But if the winds persist and allow the
warmer air to hold court, some of the QPF could fall as a
rain/snow mix, or even just rain. This would significantly reduce
accumulations.

&&

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

A deepening low over the eastern Bering will keep an active
weather pattern over Southwest Alaska for the next few days.
Strong winds, heavy snow, and visibility as low as a quarter mile
along the Kuskokwim Delta coast has already verified the Blizzard
Warning overnight as the initial front lifted northward across
the region. This warning will continue through Tuesday morning as
colder air wraps around the backside of the low, keeping the gusty
conditions and blowing snow in the forecast.

Strong winds will persists along the coastal areas, as well as
through Kamishak gap near Iliamna. A band of snow setting up over
interior Bristol Bay will keep snow falling overnight through
Tuesday morning as the surface low begins to shift inland. By
Tuesday afternoon, winds begin to taper off with snow showers
persisting throughout the day.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A broad low positioned north of Dutch Harbor this morning will
help keep strong winds in the forecast through this afternoon for
the eastern Aleutians and AKPEN. The High Wind Watch for the
AKPEN, including Cold Bay and King Cove remains in effect through
9am today. As the low tracks northward towards the Pribilofs for
this afternoon, winds along the Chain will weaken well below
warning level criteria, but still still remain gusty through
Tuesday morning. Widespread precipitation will spread across much
of the Bering with this system throughout the day.

Better model agreement in the track of this low throughout the day
has led to the issuance of a Winter Weather Advisory for the
Pribilof Islands starting at 3pm this afternoon. The compact low
northeast of St. Paul will help bring strong northwesterly winds
into the islands, along with blowing snow conditions. Expect these
conditions to continue through Tuesday as cold air advection
wraps along the backside of the low. By Tuesday afternoon, the
associated low will track into the Southwest mainland, improving
conditions across the eastern bering.

Over the western Aleutians, the next gale force low will move in
by Tuesday afternoon. The strength and position of this low are
still uncertain, so stay tuned for future forecasts of this
system.

&&

.MARINE (Days 3 through 5 Wed through Fri )...
A low over the western Aleutians Wednesday morning will slide
eastward, reaching the Gulf Thursday night and Friday. Gale
force winds are expected with this system. Some storm force winds
are possibly Wednesday and Wednesday night around the Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7 Thu through Sun)...
On Thursday morning the pattern will consist of an upper low over
the Bering Sea, with an associated trough extending southeastward
across southwest Alaska. The trough will very slowly slide
northeast across southern Alaska through Sunday as the main upper
low retreats northward. An upper level Ridge is expected to move
into the Aleutians and southern Bering as the low moves north on
Friday and Saturday. An upper level low just west of the Aleutians
on Friday will move into the western and central Aleutians Friday
night through Sunday, though the exact path and timing of this
feature is somewhat uncertain.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 145, 161, 195.
  Winter Storm Watch 131.
 Blizzard Warning 155.
         High Wind Warning 101, 181.
MARINE...Gales 125, 128-132, 150, 155, 160, 171-173, 178-180, 185, 351, 352, 412, 413, 414.
         Storms 119 165 170.
         Heavy Freezing Spray 139 179 185 412 414.
FIRE WEATHER...NONE.

&&

$$

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


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