Gale Warning 128, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKST Thu Jan 31 2019

.ANALYSIS AND UPPER LEVELS...
There is a sharp upper level ridge over western Alaska. There
is an upper level trough over northwest Canada. There is fairly
strong northerly flow aloft in between these features over
Southcentral. At the surface there is fairly strong offshore
flow from Seward eastward with strong high pressure over the
Copper River Basin. Over the Cook Inlet area and Southwest Alaska
the flow is weaker, and some stratus and fog is evident on
satellite imagery and on some surface observations. There is a
strong vertically stacked low centered to the west of the western
Aleutians. A leading front with this system extends from the
eastern Aleutians east-northeast across the Bering Sea.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for the short term
portion of the forecast (Saturday afternoon). There are some
minor differences on the exact location of some of the surface
lows, but this should have minimal impact on the forecast.
Therefore forecast confidence is higher than normal.

&&

.AVIATION...
PANC...VFR conditions this afternoon will change to generally
IFR to LIFR conditions in fog this evening through Friday
morning. Conditions should improve again Friday afternoon,
though some fog in the vicinity is possible.

&&

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

Tonight through Saturday night the ridge over the mainland will
be the dominant weather feature bringing drier and colder
conditions through. Two challenges in the near term are patchy
dense fog along the Cook Inlet and gusty winds for channeled
terrain along the coasts. Fog across the Matanuska Valley, to
Anchorage, to the western Kenai is expected to re-develop this
evening with similar slow improvement on Saturday; however,
coverage is expected to be less as the air mass is much drier
which is evident on the Anchorage 00Z sounding. Any localized
wind effects could shift the fog bank around during the early
morning. For gusty wind locations...such as Thompson Pass and
gap terrain along the coasts...expect peak gusts tonight tapering
down for Friday.

The next front moves across the southwestern Gulf Friday afternoon,
continuing on an eastward track through Friday night. A few
scattered showers are possible across the central and northern
waters just north of the low center. Wind shifts will occur as
this low tracks east, but speeds are relatively low impact with
this system.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
An upper ridge over northwest Alaska and an Arctic upper low over
northeast Alaska and the Yukon will maintain weak offshore flow
and cold dry conditions this evening. Stratus persists in the
lower Kuskokwim Valley and in the Bristol Bay area, but offshore
flow farther north was strong enough to clear out much of the
inland Kuskokwim Delta. Weak north flow along the south side of
the AKPEN also facilitated partial clearing. A vertically stacked
storm force low centered roughly 300 miles west of Attu is
gradually shifting westward toward the Kamchatka peninsula. The
occluded front associated with this low is approaching the AKPEN,
and will bring a transition to south flow and wet conditions over
most of Southwest late tonight into tomorrow. The front will
dissipate as it reaches the mainland so significant precipitation
is unlikely, with around 2 to 3 inches of snow expected in areas
closer to the coast and up to an inch farther inland.

Another storm force low will reach the western Aleutians late
Friday into Saturday, and warm air advection ahead of its front
will continue the warm up Saturday, with another round of
precipitation. Again, the front will be dissipating as it reaches
the mainland but still expect some precipitation, though with the
continuing warm-up, will probably see areas of rain or rain/snow
mix.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A storm force low roughly 300 miles west of Attu continues to
bring areas of gales to the western Aleutians and portions of
the Bering, including the Pribilofs. Winds over the Bering will
diminish somewhat during the day Friday, however another storm
force low will impact the Aleutians and Bering late Friday into
Saturday. This low will develop from a wave currently roughly 800
miles off the coast of Japan. The latest ASCAT pass already shows
storm force winds in the vicinity of the wave and the low will
quickly develop under a 170kt jet. This system will bring another
round of precip to the Aleutians and Bering, with a strong
subtropical to tropical moisture fetch.

&&

.MARINE (Days 3 through 5)...
Beginning on Sunday in the western Bering, southwest winds should
be ramping down as a low weakens and exits to the north with
generally sub gale force winds expected, though the long SW fetch
will keep seas rough, with waves heights expected to remain near
or above 20 ft. Models are showing another, weaker, low,
approaching from south of Adak by Sunday afternoon, though there
is still a fair bit of uncertainty regarding this system. As it
stands right now, this system would only bring a quick bump of
winds towards low end gales, though further intensification could
increase winds towards storm force Sunday night through Monday
night over the central Aleutians and Bering Sea. Another low
approaches the western Bering from the Sea of Okhotsk by Tuesday
afternoon, though models keep the low center over Attu with the
core of strongest winds to the south of the islands.

Conditions look to remain rather benign over the Gulf of Alaska
through Tuesday with general high pressure residing over the area
keeping the storm track just to the west.

.LONG TERM FORECAST (Days 3 through 7)...
Beginning Sunday, an upper level ridge previously entrenched over
most of the mainland will shift east with the ridge axis located
over the ALCAN border by the end of the day. Out west, an upper
level low will continue to support an active pattern with a series
of systems expected to push across the Bering into the western
mainland. The eastward shift of the ridge axis will allow these
systems to push into Southcentral with precipitation expected to
make it across the Alaskan Range by Sunday morning. Another system
pushes north across the Bering by Monday with its associated
front pushing precipitation across the southern mainland by Monday
night. The consistent southwesterly fetch will mean these systems
will be pulling up milder air with increasing chances for rain
along the coast and possibly a bit further inland. The overall
unsettled pattern looks to continue through at least the end of
next week with the upper ridge axis maintaining its position east
of Southcentral with the upper low over the Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 175 176 177.
		 Gale Warning 127 170 172 173 174 178 179 185.
		 Heavy Freezing Spray Warning 127 180.
FIRE WEATHER...NONE.

&&

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