Gale Warning 104, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 AM AKST Thu Feb 7 2019

.ANALYSIS AND UPPER LEVELS...
A ridge continues to amplify across the North Pacific and the
mainland with abundant moisture streaming up between this feature
and a low over the western Bering. A similar pattern is reflected
at the surface with gusty winds surrounding the Bering low. A
front draped across the eastern Bering to the west coastal
locations is bringing continuous rain along the Kuskokwim Delta.
A warm maritime air mass has pushed across the Southwest with
temperatures in the mid 30 to near 40 degrees, meanwhile
Southcentral remains at or below freezing except for the southern
tip of the Kenai.

&&

.MODEL DISCUSSION...
Models are generally in good agreement through the end of the week
keeping the most active weather pattern over the Bering and
Southwest mainland. There are some differences on how quickly the
ridge breaks down this weekend; however, kept Southcentral and the
Gulf in a drier pattern through Saturday as models agree with the
ridge axis over the Gulf. All models are showing a quick break
down of the ridge pattern heading into Sunday.

&&

.AVIATION...
PANC...Low stratus and fog are expected to improve later this
afternoon with VFR for tonight. There is still some uncertainty on
this improvement lasting through tonight as moisture advects
north, so kept a minimal low level deck and will re-evaluate this
on the next TAF package. Winds will generally be light through
early Friday afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
High pressure will remain over Southcentral through Friday night.
Considerable moisture is trapped underneath this ridge, with
plenty of low stratus and some patchy fog. With the upper level
ridge axis near the Canadian border, there are also some high
clouds over the area. Most areas will not see any precipitation
for the next couple of days. The main exception is the Susitna
Valley, where some weak systems "topping" the ridge bring some
chances of snow. There is also a chance for some precipitation
this morning over the western Kenai Peninsula, as a weak system to
the west of the area moves north.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3; Thursday
through Saturday Night)...

An active weather pattern remains over southwest Alaska as the
region sits at the transition between the long wave trough axis
over the Bering and the ridge axis over the Gulf. This is
producing a long southwesterly fetch from the sub-tropical Pacific
north across the AKPEN and YK-Delta and bringing with it plenty of
moisture (PWAT of 0.59" at PABE at the 12z sounding) and warmer
air (current temps in the mid 30s to mid 40s for all but far
interior sections). A primarily rain event will continue today for
locations along the coast and across the Lower Kuskokwim Delta as
a surface low over the eastern Bering pushes a warm front north
of the region. Southerly winds will also remain gusty as a strong
low-level jet (62kts at 925mb over Bethel at 12z) continues to
race over the region. A trailing cold front then moves in tonight
with enough cold air behind it to change the rain back to snow,
especially for areas north of Dillingham. Only minor accumulations
are expected with this system; however, a brief period of
moderate to heavy snow cannot be ruled out for places like Bethel
as the front pushes through given the abundance of moisture and
strong upper-level dynamics.

Conditions then slowly improve for all but the AKPEN and Bristol
Bay regions on Friday as the front continues east and stalls
along the Alaska and Aleutians Ranges. A ridge settling in over
the YK Delta will bring clear and drier conditions while areas
south and east remain warmer and wet (with snow for the far
interior and higher elevations).

The next frontal system then moves toward the region for Saturday
bringing another surge of warm, moist air on strong southerly
winds. Much like the current system, a few sheltered valley
locations where colder air is trapped at the surface may see a
brief period of snow at the onset of precipitation. However, as
warmer air quickly moves in, this will become another primarily
rain event with temperatures again climbing into the mid 30s to
mid 40s. As the front moves across the region Saturday night,
colder air behind it will again change the rain back to snow.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3;
Thursday through Saturday Night)...

A trough digging through the Bering continues to bring warmer air,
rain, and gusty southerly winds to the eastern Aleutians. The
surface low associated with the upper-level trough will move north
today with its trailing cold front sliding east over the AKPEN,
ending the precipitation and gusty winds for the eastern half of
the chain. A compact gale-force low will skirt the western and
central Aleutians today, but weaken as it slides south of the
eastern Aleutians. Attention then shifts west to a rapidly
deepening low approaching the ALeutians west of Shemya tonight.
This system will bring a surge of warm air across the Aleutians
along with widespread storm-force winds and even hurricane-force
winds for the western-most zones Friday. This system lifts quickly
into the northern Bering as a second area of storm-force
southerly winds move across the central Bering along its occluded
front.

&&

.MARINE (Days 3 through 5)...

Beginning Friday, there is generally good confidence that a ~970
mb low will track just to the west of Attu bringing a wide swath
of southwesterly gale force winds to the Bering/Aleutians west of
the Pribilofs through Friday night. There is also the chance for
some areas of storm force winds to develop over the western
Aleutians/Bering by Friday evening, though these are not expected
to be long lived. Winds and waves are expected to subside some as
the low pushes north by Saturday morning, with generally high
confidence that winds further diminish Saturday night into Sunday
as ridging temporarily builds in over the western Bering.
Confidence is increasing regarding a strong ~960 mb low
approaching the western Aleutians from the southwest by Sunday
afternoon. The initial front associated with this low is likely to
produce gale force winds from the southeast across most of the
Bering. There is also increasing probability that a swath of storm
force winds will push through the western Bering/Aleutians by
Sunday night.

Over the Gulf of Alaska, high pressure will generally lead to
tranquil conditions through Saturday. By Sunday, a low is expected
to approach the western Gulf, though there is still a fair amount
of disagreement regarding this system. Generally expect winds and
waves to increase over the western Gulf through the day on Sunday.

&&

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

Beginning Friday, an upper level ridge will dominate the long wave
pattern over most of the Gulf of Alaska and the eastern mainland.
An upper trough will be located over the western Bering leading to
an active storm track across the western half of the area. Strong
southerly flow in between the ridge and trough will pump warm and
moist air north into the southern mainland, with precipitation,
mostly as rain, expected over the southwest mainland Friday and
Saturday. The forecast challenge will be determining how far east
the ridge axis pushes and weakens over the weekend. The GFS keeps
the ridge a bit further east and flattens it, allowing the storm
track from the Bering to push further east into Southcentral,
while the EC amplifies the ridge, leading to more of a blocking
pattern. Regardless, both solutions show a system pushing a front
into the western Gulf by Sunday, bringing increasing chances of
precipitation to Southcentral, especially along the coast.

By Sunday, a strong cold front looks to push east across the
Bering and mainland nudging the upper ridge to the east. This
will bring precipitation across most the southern mainland with
colder air pushing in behind the front through Monday morning. An
even stronger low will push east across the Bering on Monday
bringing a wide swath of precipitation across the mainland through
Tuesday with a surge of warmer air ahead of the system, thus
precipitation types will be challenging.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 155 160 165 175 176 180 185.
         Storms 177 411 412 413.
         Hurricane Force 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...KVP