Small Craft Advisory 246, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
821 AM AKDT Fri Mar 23 2018

.ANALYSIS AND UPPER LEVELS...

The upper level omega block over the area is beginning to break
down this morning as a strong upper level low, over eastern
Russia, and it's associated trough over the eastern Bering
continue to move eastward. This results in an eastward shift in
the pattern. Mid-level atmospheric temperatures continue to warm
as the ridge moves over Southcentral, though from here, the ridge
will be weakening so the warming in the mid-levels is just about
over. Fortunately, the 12Z Anchorage sounding remains similar to
previous ones in the sense that the entire atmosphere is very dry.
Thus, fog concerns remain minimal this morning. As the upper
ridge weakens, the flow on the east side of the ridge across the
Copper Basin and southeastern Prince William Sound is also
diminishing. The very strong winds we have seen through that area,
especially Thompson Pass, are also gradually weakening.

Across Southwest Alaska, a dying cold front marking the eastern
edge of the colder air, produced some snow over the Kuskokwim
Delta yesterday evening. This localized addition of moisture along
with onshore flow could result in some fog concerns as well until
sunrise. The front has moved into the Bristol Bay area causing
localized very light snow. As the morning progresses, the snow
will dissipate. Across the Bering, the cold air in place through
the upper levels has made the atmosphere through that area very
unstable thus resulting in a large cumulus field over the area.
Fortunately, no individual clusters have thus far been able to
become thunderstorms. The off-and-on snow shower activity
continues over the Pribilofs with individual snow showers briefly
dropping visibilities as low as 1 mile.

&&

.MODEL DISCUSSION...

The models are in decent agreement over the next two days on the
evolution on the broad synoptic setup. The GFS is a bit stronger
and further north than the other models with the low by late
Saturday night. Thus an EC/NAM solution was used out west. No
real differences exist between any of the models in the
Gulf/Southcentral, so high resolution models were used for the
winds. Forecast confidence remains high.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Localized gap winds along the north Gulf coast and Prince William
Sound will finally die down today as a weakening upper level ridge
moves overhead and surface pressure gradients slacken. An elongating
and weakening front over Southwest Alaska will make its way into
the western Gulf and Southcentral this afternoon, with very little
precipitation surviving the journey across the Aleutian/Alaska
Ranges. Increasing mid to high clouds for western-most areas will
be the main impact. Weak cold air advection combined with
tightening pressure gradients as a ridge builds over Southwest
Alaska will lead to gusty gap winds across the western Gulf/Kodiak
Island beginning late this afternoon and continuing through early
Saturday. Slightly cooler air and tighter pressure gradients will
also bring another round of wind to gaps along the north Gulf
coast and Prince William Sound, albeit notably weaker than the
wind event of the past few days.

For most of the region dry conditions and seasonable temperatures
will be the norm for the next couple days. The next chance for
precipitation will come with a frontal system moving into the
southwestern Gulf Saturday night, with snow and strengthening
winds for Kodiak Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
The frontal system currently stretched from the Lower Kuskokwim
south across the greater Bristol Bay area will continue to shear
apart as it continues slowly east today accompanied by a cold
upper level trough. Flat ridging will briefly build over Southwest
Alaska late Friday night through Saturday morning. The next
frontal system will begin spreading across the Alaska Peninsula
Saturday and then lift northeast into Southwest Alaska Saturday
night through Sunday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
As the most recent Bering low lifts away to the north and into
Russia, the next developing North Pacific low is approaching the
western Aleutians this morning. The surface low will cross the
Aleutian chain just to west of Kiska this evening and then
continue into the central Bering through Saturday. The low will
become vertically stacked as it crosses the Pribilof Islands
Sunday afternoon and evening, then continue drifting slowly east
northeast to reach the Kuskokwim Delta Coast around Tuesday
morning.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A brief pattern change will begin on Sunday, as the ridge in the
North Pacific weakens slightly and moves southward. This will
allow the low pressure systems that have been remaining in the
western portion of the area to move eastward, affecting more of the
mainland. On Sunday, a triple point low will develop along the
front south of the Aleutians, then strengthen as it moves into the
Gulf of Alaska. This will bring weather onshore for the Gulf Coast
region. However, the system will weaken rapidly as it heads
northward over the mainland and precipitation will diminish for
interior regions on Monday. By Tuesday, forecast continuity
between the model solutions begins to struggle. Earlier runs
indicated that the ridging would build back in to the North
Pacific, which would bring a very spring-like pattern to the
forecast area. However, this afternoon's runs have diverged,
instead bringing a strong low into the Gulf of Alaska. This brings
low confidence to the extended forecast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales: 130 131 176 177.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JER
LONG TERM...LF