Small Craft Advisory 783, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 PM AKDT TUE OCT 4 2016

.ANALYSIS AND UPPER LEVELS...
An upper level ridge of high pressure has set up over mainland
Alaska, with a long wave trough extending from the Kamchatka
Peninsula through the eastern Bering Sea. Further west, a strong
upper level low is moving northeastward from the northern Pacific
towards the western Aleutian Islands. This upper level feature is
reflected in the lower levels by a strong surface low and is
supported by a 130 knot jet digging into the base of the trough.
The accompanying front is quite strong, with storm force winds
expected in the Aleutians later today. The cold pool aloft behind
the front is enhancing the instability along the occluded front
and several active areas of thunderstorms have been observed in
the Northern Pacific this morning.

Further east, the upper level trough across the Bering is swinging
a weakening front through the eastern Aleutians and western
portion of the AK Pen. The strong ridge over the mainland is
holding this system at bay, so any low clouds and precipitation
associated with this feature are restricted to the Bering Sea
communities. As for the mainland, some weak troughs moving down
from the Interior did bring showers overnight, which has
contributed to some lingering low clouds in a few areas.
Otherwise, weather across the mainland is mild and fairly sunny,
with some weak outflow bringing gusty winds around 20 mph to
northerly-oriented bays and passes.

&&

.MODEL DISCUSSION...
Models are in good agreement this morning on all features. NAM was
used for details in the short term with GFS reflecting the longer
term pattern.

&&

.AVIATION...
PANC...A SCT low deck is still lingering around PANC this morning
but the clouds are primarily confined to the Anchorage bowl. The
expectation is that the clouds will clear over PANC today and VFR
conditions will prevail through most of the night, although there
is a risk for fog with very light northerly flow and the residual
moisture from last night's showers. The current TAF reflects this
concern. If the current BKN decks do not dissipate enough for
overnight clearing, fog should not be an issue for tomorrow
morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Upper level high pressure will slowly build in from the west and
northwest through Thursday afternoon. The stubborn but weak upper
level trough that has been over the area the last few days will
stretch out and weaken tonight. This will allow skies to clear
considerably. Offshore flow will slowly strengthen through
Thursday morning, but will not be particularly strong. Some patchy
fog is possible in the morning from the Kenai peninsula northward
into the Susitna and Matanuska valleys on Wednesday with the light
low level flow and some lingering moisture.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure building over the area will bring generally
tranquil weather to the area through Thursday. One exception to
this will be along the Kuskokwim Delta coast where the remnants of
a frontal system moving through the eastern Bering will bring rain
showers and gusty southeasterly winds to that area, but with
ridging holding over the Mainland this is not expected to move
inland. For interior areas the focus will be centered around the
potential for fog and stratus development over the next few
nights. Currently it doesn't appear that subsidence from the
ridging will be strong enough tonight to produce widespread fog or
stratus, but patchy areas could certainly be possible. Otherwise
sunny skies should prevail into Thursday with seasonable
temperatures and light winds.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A very active and progressive pattern will continue into Thursday.
The gale force low currently departing the northern Bering is
quickly being followed by a storm force low currently approaching
the western Aleutians. There is a chance that thunderstorms that
have been firing behind the front from this system today will
spread into the western Aleutians late tonight, so these were
added for late tonight. These thunderstorms should then diminish
Wednesday afternoon as instability begins to weaken. This low will
then spread heavy rain and storm force winds from the central
Aleutians into Pribilof's for Wednesday. This active pattern will
continue even further as the remnants of Super Typhoon Chaba will
begin to approach the western Aleutians late Thursday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Guidance continues to get a better handle on what the remnants of
Super Typhoon Chaba will do as it approaches the Western
Aleutians. With all the models holding strong high pressure over
mainland Alaska from Thursday through the weekend, they all keep
the remnants of Chaba well to the west of mainland Alaska. It
looks to move into the central Bering late Friday and then turn to
the northwest as it weakens through the weekend. There is also
better agreement with the winds associated with this storm that
look to bring storm force winds to marine areas on the Pacific
side of the Western Aleutians Thursday night and Friday. For
mainland Alaska the aforementioned high pressure will keep the
skies mostly clear through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storms 173 174 175 176.
         Gales 155 165 170 171 172 177 178 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...DK