Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 181229
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
429 AM AKDT Sat Mar 18 2017
.ANALYSIS AND UPPER LEVELS...
A blocking upper level ridge remains in place over much of the
Bering. East of the ridge is a broad upper level trough over the
Southern Mainland and Gulf, and to the west is a closed upper
level low southwest of the Western Aleutians. At the surface, low
pressure over the gulf continues to produce a tight pressure
gradient over the northern Gulf Coast, resulting in gusty winds
over the areas surrounding Prince William Sound. Except for cloudy
conditions with a little light snow along the Northern Delta
Coast this morning, mostly clear skies and dry offshore flow
conditions continue across the much of the Southern Mainland. A
stalled front over the western/central Aleutians and Bering
continues to bring some rain, with small craft to gale force
easterly winds to the area.
Models remain in fairly good agreement through much of the short
term forecast. Some minor model differences appear in the day 3
time frame regarding the timing of an upper level wave dropping
southward over the Susitna Valley and Cook inlet region Monday.
This creates some uncertainty with the timing of when the
stronger winds will mix down from aloft, and where the core of
strongest winds will set up. Current guidance is showing the winds
picking up over these areas in the afternoon or Evening on
Monday. The NAM is showing the strongest winds setting up mainly
over Cook Inlet and Susitna Valley. However, the GFS and EC are
both showing the stronger winds stretching southward from the
Susitna Valley and further eastward over Cook Inlet and the
Western Kenai Coast. The NAM and GFS were the preferred models for
this forecast package, and a middle ground blend was used for the
above mentioned differences.
PANC...VFR conditions and light winds will persist.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Another day of clear and cold weather is on tap for Southcentral
Alaska today. However there is a little bit of a change underway
as the upper level low that has moved over the area from the north
will cause a surface low to develop in the northern Gulf of
Alaska today. This low will become the source of some clouds that
will push inland tonight into Sunday. It will also bring a good
shot of snow showers for areas along the north Gulf Coast
including the Prince William Sounds region by Sunday as well.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
More of the same is in store for the Southwest Alaska as dry
northerly flow continues to support cold, dry, and predominantly
sunny conditions through the weekend. The exception will be along
a narrow coastal corridor from Kipnuk to Hooper Bay, where an
upper level disturbance dropping down from the north may be
sufficient to generate a few light snow showers through this
afternoon. This feature will also serve to reinforce the mainland
trough with more arctic air, helping to keep temperatures running
well below seasonal normal values for the next few days.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The fairly weak front over the Western Bering will continue to
lift to the north and east towards the Pribilofs and Eastern
Aleutians tonight, then stall out and dissipate on Sunday as it
encounters the stout ridge over the Eastern Bering. This will
generally mean Small Craft Advisory to weak gale force winds and
light rain across the Aleutians, with a second front moving over
the western and central parts of the chain late Sunday. Areas
farther to the east such as the Alaska Peninsula will see
continued dry and partly sunny conditions through the weekend
beneath the ridge.
.LONG TERM FORECAST (Days 3 through 7)...
The persistent Bering ridge resides nearly in place through the
end of next week. This keeps weather trends largely the same into
the extended forecast with he most active weather pattern over
the western Bering as a parent low just south of the Kamchatka
Peninsula ushers multiple fronts toward the western Aleutian
Chain. The southern mainland stays under dry conditions with
temperatures cooler than normal, however daytime highs will
moderate slightly warmer for the next work week. Across the Gulf
of Alaska, low pressure re-develops along the western gulf into
Monday continuing snow along the area waters along with higher
chances for snow along the coastal communities. The gulf low
diminishes by Tuesday, however a weak trough axis remains over
the central to northeast waters.
A pattern shift is anticipated for mid to late next week
as the polar jet weakens over the northwest mainland while at the
same time, the subtropical jet amplifies and shifts toward the
Bering. Models have been picking up on this solution for several
runs, so there is high confidence that a storm system develops and
kicks the stagnant pattern into motion.
MARINE...Heavy Freezing Spray Warning...121 126 127 129 130 138
139 150 185.
SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB