Gale Warning 198, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Mon Mar 4 2019

.ANALYSIS AND UPPER LEVELS...
The pattern is becoming more progressive with the upper level
ridge over Southcentral Alaska moving eastward which is allowing
the trough in the Bering Sea to push eastward as well. There is a
decent jet streak in the eastern Bering Sea between these features
with 250 mb winds from the south between 95 and 115 kt. This
enhanced lifting associated with the jet streak can be seen on
satellite ahead of the surface front with a moisture tap that
extends to near 30N. Some weaker lows are also visible on
satellite over more western parts of the Bering Sea with the next
big low beginning to be show up well to the southwest of Attu.

&&

.MODEL DISCUSSION...
Models are continuing to initialize well and remain in generally
good agreement through much of the week. With that said, there is
some minor 'sloppiness' in the Gulf Wednesday with a trough with
an embedded low moves through that area. Models all are in
agreement with the trough location and timing, but there is a
discrepancy on the location of the weak low. The GFS and NAM have
it tracking over Kodiak Islands while the ECMWF and Canadian have
it 100 to 200 miles farther south. The large low that will move
into the western Aleutians Wednesday has great agreement between
the four models and then they start to separate on Thursday in
the speed of the low through the southern Bering Sea, but agree
on the track.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. The stratus
that developed last night is unlikely to become widespread enough
to cause ceilings near the airport due to mid and high level
clouds moving over the region.

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

An weakening upper-level ridge sliding east from the western Gulf to
the central Gulf will continue to keep most of Southcentral dry
overnight, with only increasing high clouds across the region and
areas of low stratus along the Copper River Basin. Farther west,
the advancing shortwave kicking the ridge east will bring thicker
cloud cover and precipitation to Kodiak Island tonight. This area
of clouds and precipitation will lift slowly north across the
Kenai Peninsula and into the Susitna Valley for Tuesday. Areas
along the lee of the Kenai and Chugach Mountains will stay
primarily dry, however, due to the southerly, cross-barrier flow
aloft. The surface trough associated with the shortwave will stall
and weaken through Tuesday, as it runs into the ridge in the
central Gulf and the upper-level support outruns the surface
feature. A second surface low developing southwest of Kodiak
Island Tuesday will then lift northeast, absorbing the remnants of
the first system and enhancing precipitation from Kodiak Island
north and east along the Kenai and Alaska through Wednesday. This
low will stall and weaken by late Wednesday as it, too, runs into
the ridge and the upper-level support decouples from the surface
feature.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Tonight
through Wednesday afternoon)...

A strong ridge in place over Southcentral has prohibited an
incoming front from continuing to move eastward. This has forced
the front to stall over the Southwest coast, and as a result,
pressure gradients have increased along the west side of the
Alaska Range. This will cause gusty southerly winds to increase
during the evening hours with enhanced flow through the usual gaps
and passes along the AKPEN tonight. Temperatures will continue to
warm through the evening with precipitation falling as rain in
most places. Colder temperatures over interior Southwest will
allow for a rain/snow mix. By Tuesday morning, an upper level jet
streak helps to enhance flow upstream and allows the ridge to
weaken slightly. This will allow for the front to drift eastward
and eventually dissipate Tuesday evening. In its wake, a ridge
over the eastern Bering approaches the southwest coast, bringing
westerly flow and generally colder air. As the ridge encourages
weak onshore flow for Wednesday morning, areas of fog will likely
develop, especially along the coast. Areas of fog may persist
through Wednesday afternoon along the coastal areas of Bristol
Bay.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Tonight
through Wednesday afternoon)...

A front over the eastern Bering has stalled, allowing for the
western Bering to largely remain under westerly flow with
scattered snow showers. The real story for the Bering this week
will be an approaching storm force low with a leading front
arriving over the western Aleutians Tuesday morning. Amid a large
area of gales, an area of southerly storm force winds will cross
over the western Aleutians and reach the central Aleutians for
Tuesday evening. This front will bring another round of warm
southerly flow, allowing for precipitation to fall mainly as
rain. As the low continues on an easterly track, the leading storm
force front will reach the eastern Aleutians by Wednesday morning
while the low center passes just south of Shemya Wednesday
afternoon. Another round of storm force winds is expected on the
back side of the low as cold air wraps in behind it allowing
strong west to southwest flow over the western Aleutians for
Wednesday evening.

&&

.MARINE (Days 3 through 5)...

On Thursday a storm force low tracks across the southern Bering at
960 mb then fills quickly on Friday as it moves south of the
Pribilof Islands to the Alaska Peninsula. The next front pushes
to the western Aleutians Friday morning as a North Pacific low
races toward the Bering. The low along the southeastern waters
dissipates Friday night as the other powerful low moves toward
Kiska at 951 mb. This storm is expected to take a similar
southerly track through Saturday; however, it is expected to stay
organized as it tracks eastward. The low center does move slightly
slower as the other eastern Bering system breaks down over Bristol
Bay. The new storm center moves to near Adak at 960 mb Saturday
afternoon.

&&

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

The long range forecast beginning Thursday is an active pattern
with a storm system tracking across the southern Bering...pushing
a front across the southern mainland and the Gulf through early
Saturday. The next system to move across the Bering enters the
western Aleutian Chain on Friday night, taking a similar track
through Sunday morning. Models are generally in good agreement
with the overall synoptic pattern; however, there are important
differences with each new model run on the evolution of the low's
track over the weekend. The blends of the ensemble ECMWF and GFS
were used for updates today which continues to advertise a wetter
and windier pattern. The highest uncertainty on this low is how
far east the low tracks. Previous model runs all indicated that
the low would lift north across the eastern Bering...and now they
are showing either a triple point low developing in the Gulf or
the storm system remaining on an easterly track. Either solution
brings a forthcoming pattern change heading to the beginning of
next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storms 175-178 411 413 1500 155 160 173 174.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO/SEB
MARINE/LONG TERM...KH