Brisk Wind Advisory 17, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
643 AM AKST Fri Jan 31 2020

.ANALYSIS AND UPPER LEVELS...
A broad upper level trough is over the mainland with a closed low
center spinning over the western Gulf of Alaska. This low remains
stagnant since Thursday as an upper level ridge pattern borders
it to the east and west. Farther west, an upper low is spinning
along the northern Kamchatka Peninsula. At the surface, scattered
snow showers continue to develop across the Gulf and eastern Bering
along with upper level shortwaves propagating around the Gulf low. A
few showers are moving into the surrounding coasts before
dissipating.

&&

.MODEL DISCUSSION...
Models continue in good synoptic agreement through the weekend
with the low over the Gulf exiting southeast followed by another
strong storm moving to the Western and Central Aleutians on
Saturday. Only minor changes were made for the morning forecast
package with most of the edits focused around increasing winds
along the Gulf coasts as cold air advects from the north. Hi-res
models were used to update the forecast across Southcentral and
the Gulf with use of the GFS across the Southwest and Bering.

&&

.AVIATION...
PANC...MVFR ceilings are expected to improve to VFR this morning
then remain VFR through late Saturday morning. Winds will be
relatively light with a prevailing north wind setting up as
offshore flow develops this afternoon.

&&

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

A trough lifting over Southcentral Alaska this morning is
responsible for snow showers over the Gulf into Prince William
Sound. This afternoon, a second shortwave trough will spread snow
showers farther inland, including into the Copper River Basin.
The brunt of showers with this second short-wave will move across
Cordova and vicinity, with locally heavy snow possible producing
a few inches of snow.

In the upper levels, a ridge over the Bering Sea continues to
move eastward along with an upper level jet and weak cold air
advection on the front side of this ridge. This will keep strong
winds and gusts in the forecast for bays and passes along Shelikof
Strait, as well as Kamishak Bay to the Barren Islands. These winds
will quickly diminish Saturday evening as the ridge moves into the
western Gulf and pressure gradients weaken.

As the ridge approaches Southcentral later today through
Saturday, pressure gradients will tighten along the north Gulf
coast and Prince William Sound, particularly for Passage Canal
and Resurrection Bay. Winds over these areas have been increased
for today's forecast with a much more impressive pressure gradient
in today's models along with favorable flow aloft. Expect the
strongest winds late tonight through Saturday morning followed by
weakening winds as the ridge begins to move in over Southcentral
Saturday night.

&&

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

Upper level troughing and low level cyclonic flow continues to
dominate the region as bitterly cold temps remain in place. Snow
showers are still impacting the Southern Alaska Peninsula but
these will diminish today. Surface high pressure will strengthen
through Saturday morning until a significant warm front begins to
impact the coast Saturday afternoon as a leading weak wave moves
through the Kuskokwim Delta. The big warm front moves in on Sunday
morning, and this will likely bring accumulating snow and blowing
snow impacts to Southwest as the pattern shifts dramatically.

&&

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

An upper level mobile shortwave trough is slowly moving east
across the western Bering Sea with the surface trough axis
extending from Nikolski to the southern tip of Eastern Siberia.
This is bringing rain/snow to the Central Aleutians, and as the
trough shifts east and consolidates, light snow accumulations
will impact the Pribilof Islands and Unalaska/Akun.

Attention rapidly turns to a quickly developing bomb cyclone which
will spread snow into the western Bering/Aleutians today. The warm
front associated with this low will move into the Bering Sea
tonight and Saturday, then reach the Southwest coast by Sunday
afternoon. Snow will initially accompany the front along with
quick accumulations, but this front will bring in enough warm air
for the entire Aleutian Chain to turn to rain as the front lifts
north. The one concern will be 3-5" snow and strong east winds
impacting the Pribilof Islands with snow/blowing snow, so this
will need to be monitored as we get closer.

&&

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

Bering Sea and Aleutian Coastal Waters: A ~950 mb low will be
located near the Rat Islands Sunday afternoon, with sustained
high-end gales and storm force gusts expected on the backside of
this system across the western Aleutians and Bering. The low then
moves to just west of the Pribilof Islands by Tuesday, with
sustained winds having decreased below gales by then.

As for seas, given a long dynamic fetch, seas of 25 to 30 feet are
anticipated on Sunday across the western Bering and south of the
Aleutian chain west of Dutch Harbor decreasing into the 5 to 15 feet
range north of the Chain and east of 175W. These waves then subside
further for Monday and Tuesday as the storm system weakens.

Gulf of Alaska: A sustained gale force front will enter the Gulf
on Sunday from west to east, before the front stretches out
parallel to the coast on Monday as it weakens. As it does so
winds will decrease towards the small craft variety, with a few
gales still possible near the Copper River Delta. By Tuesday winds
will remain below 20 knots. As the front crosses the region, waves
will build into the 15 to 20 feet range for Sunday into Monday
before decreasing on Tuesday.

&&

.LONG TERM FORECAST (Days 4 through 7, Monday through Thursday)...
A pattern change looks to commence over the next several days as a
fairly strong storm system reaches the west central Aleutians
Tuesday morning, moving into the Pribilof Islands by later that
evening. As it does so a warm front will surge north and east
bringing increased warmth and moisture aloft, which translates to
temperatures moderating towards normal for the middle portion of the
week for the central Aleutians eastward through Southwest and
Southcentral Alaska. Precipitation potential will also increase
ahead of these features.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 130 174 176 177 178 185.
         Gale Warning 120 121 129 131 132 136 138
                      150 155 170 171 172 173 175 185.
         Heavy Freezing Spray Warning 120 121 129 130 131 132
                                  136 137 138 139 141 150 165.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KH
SOUTHCENTRAL ALASKA...AH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
MARINE/LONG TERM...PD