Small Craft Advisory 427, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
607 PM AKDT Sat May 26 2018

Resent with updated Long Term Discussion...

.ANALYSIS AND UPPER LEVELS...
A nearly stationary gale force low centered over the Eastern Gulf
continues to bring primarily just cloud cover to the Gulf Coast
and areas of Southcentral, but this is beginning to clear as high
pressure from the Mainland approaches from the west. Slightly
further to the north from the Kuskokwim Valley into the Copper
River Basin skies were clear for much of the morning, allowing for
enough heating to allow for convection to begin developing by
early this afternoon. This is occurring along the southern edge
of the thermal trough that stretches into the interior, and will
the focus for isolated thunderstorm activity this weekend. The
weak ridging over the Mainland is much stronger and widespread,
which has allowed for widespread stratus to continue over much of
that area. Gusty northwesterly winds are also blowing from the
Eastern Bering into the AK Pen, which should continue into late
Sunday as the ridge axis approaches from the west.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement through the
holiday weekend, so forecast confidence remains generally good.
There is some question as to how much shower activity will
continue into late this evening from the weak easterly wave that
will rotate around the Gulf low, leading to slightly lower
confidence in the rainfall forecast over the Gulf Coast and
Southcentral overnight tonight.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)... As
the low in the eastern Gulf weakens through Sunday the thermal
trough will push south through Southcentral Alaska. This will
allow for diurnal showers around the area with the chance for
thunderstorms to develop in areas around the Copper River Basin,
Talkeetna Mountains and the Alaska Range this afternoon/evening.
This setup will remain similar on Sunday with the chance for
thunderstorms extending south to the western Chugach and Kenai
Mountains. The diurnal pattern will also allow for some clearing
of cloud cover overnight into the early afternoon with
temperatures reaching the mid 60s in the Susitna Valley and
western Kenai Peninsula Sunday afternoon.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Thunderstorms are already firing in the Southern Kuskokwim Valley
and Bristol Bay and are expected to continue through the evening
with the unstable air aloft. By tomorrow, the thermal trough will
weaken and move slightly eastward, which will limit the chance for
thunderstorms to the northeast corner of the area, up near the
Alaska range. Elsewhere in Southwest, Sunday should be a fairly
nice day, although along the Kuskokwim coast, clouds may prevail
with a chance of fog in the morning as the northwest flow brings
more moisture to the area. The upper level ridge continues to move
eastward over the area on Monday, continuing dry and stable
conditions before a front brings rain to the outer coast starting
Monday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The ridge in place over the Bering Sea today continues a pattern
of low clouds across most of the region, although the far Western
Aleutians is beginning to see the effects of an approaching front.
This front will continue to move across the Bering Sea tomorrow
and Monday as its parent low moves northward towards the
Kamchatka peninsula. As a developing wave moves into the base of
the trough near the central Aleutians, the force will become a
gale force front with the possibility of a few storm force gusts
south of the chain. By Monday night, the front will have crossed
much of the Bering Sea, switching the winds to mainly southwest
and bringing the parent low down from the north. Air aloft
associated with this system is fairly warm, so strong winds are
not expected behind the front and the precip will remain liquid.
&&

.LONG TERM FORECAST (Days 3 through 7...Tue through Sat)...
As is often the case with the extend portion of the forecast,
there is decent agreement among the models early on before slowly
(and surely) starting to diverge from one another. This leads to
fairly high confidence in the pattern to start the week, but lower
and lower confidence as we move towards the first weekend in
June. To start things off, a low over the Western Bering will
continue to weaken as it slings a front through the West Coast.
This will make for rather dreary, wet, and windy day for SW AK Tue.
Convection (mostly showers with some isolated thunderstorms) will
be likely east of the AK/Aleutian Ranges across the rest of
southern AK. The front shears apart in the lower elevations as it
tries to cross those mountain ranges into Wed. However, the more
potent upper- level trough will eject over the southern mainland.
With plenty of low-level moisture, moderate instability with a
cold pocket aloft, and decent lift, expect showers to encompass
most of the mainland. The heaviest precipitation will fall over
the southwest. This trough could also drop 850mb (5,000')
temperatures about 5 degrees Celsius making both Wed and Thu
rather cool and wet.

However, by late Thu-early Fri, most models are now pointing to a
fairly strong noise of a ridge from the Pacific pushing into the
state. This would dramatically change the weather to a much drier
and warmer pattern. Most models hint at this feature at least
lasting 1-2 days. But the ECMWF is showing signs of closing off
the high. If this were to happen, we could move into a very
summer-like pattern for much of the early part of June. As we said
at the onset of the discussion, the farther out in time, the less
we rely on any given solution. However we have trended the
forecast slightly warmer and drier for next weekend and we will be
monitoring the progress of the ridge.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 173-176.

&&

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