Small Craft Advisory 245, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
419 PM AKDT Wed Mar 22 2017

.ANALYSIS AND UPPER LEVELS...
An upper trough which has been stationary over Southcentral has
developed into a closed low and is now beginning to sink southward
as a short-wave over northern Alaska drops into the back side of
the long-wave trough. With continued low level offshore flow and
the lack of any organized system over the Gulf, the only impact of
the upper low is a few clouds and isolated snow showers over the
mountains of eastern Prince William Sound on up into the Copper
River Basin. Otherwise, dry and cool conditions with locally gusty
winds (primarily along the coast) continue across Southcentral and
all the way west to the eastern half of the Bering Sea under the
influence of the blocking high.

Conditions out west along the Aleutians are quite benign as well
with a weak low passing to the west across the far western Bering
Sea. Meanwhile, a very large deep low over the northwest Pacific
is slowly tracking toward the Aleutians. This will be the first
major storm system to affect the region in quite some time and
will be the lead-in to what will become a significant pattern
change for all of Alaska.

&&

.MODEL DISCUSSION...
Models remain in good agreement over the next couple days and
forecast confidence is high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

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

A weakening low pressure center in the Gulf will send more clouds
and isolated snow showers across eastern Prince William Sound
tonight into Thu. Otherwise sunny and slowly warming days with
clear and cold nights will continue through Fri. Locally gusty
north winds through channeled terrain are also expected during the
period.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Northerly flow and generally sunny skies will continue over the
region into late in the work week as a ridge of high pressure
remains over the Eastern Bering. One exception to this will be
over the Kuskokwim Valley which will see a slight increase in
cloudcover and a chance of flurries as a shortwave descending
from the western interior clips the area on Thursday. This feature
is both drier and weaker than initially expected, so any flurries
that do develop should be brief. Northerly flow will then increase
on Saturday as a weakening gale force front spreads into the
Bering, but with otherwise sunny and dry weather.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Most of the Bering Sea will see one more day of benign weather on
Thursday in advance of the next frontal system that will move into
the Western Bering beginning late Thursday. This system will
spread gale force winds and rain throughout much of the Bering and
Aleutians to the west of the Pribilof Islands for Friday and
Saturday.

&&

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

Northwest upper level flow and ridging over the Bering will remain
dominant as the extended period forecast begins Friday evening.
At the same time a sprawling low over the North Pacific extending
into the southwest Bering Sea will be slowly moving east. This
means the sensible weather pattern of mostly dry and offshore flow
over Southern Alaska will still be dominant before larger changes
begin to develop Sunday and into next week. After weeks of
dominant ridging over the Bering Sea, this feature will begin to
weaken and retrograde northwest, allowing for a pattern change as
the arctic trough over Southern Alaska merges with a series of
weak North Pacific lows. Right now, there is uncertainty of
exactly where the arctic trough stalls, but it is most likely that
the trough stalls near the Alaska Range with most of the
precipitation (rain and snow along the coast) remaining east of
the Alaska Range. By midweek and beyond, uncertainty grows with
the details, but it seems quite likely, based on the shifting
blocking high, that storminess will be on the increase as the NPAC
jet strengthens and amplifies.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Heavy Freezing Spray 121 126 127 129.
Gale 174 175 176 177 178

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JA