Small Craft Advisory 434, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
825 PM AKDT Sat Jun 8 2019

Updated for Marine and Long Term Discussion

The overall upper level pattern remain similar from the past few
days with ridging over the central Bering Sea and a weak upper
level trough over Southwest mainland Alaska. Very weak flow
remains over mainland Alaska.

The main difference in the region has to do with the areas of
greatest instability. The main area of instability is now over
the Kuskokwim Valley southward into Bristol Bay. However and area
of unstable air remains over the Susitna Valley to the northern
half of the Copper River Basin. The Kenai Peninsula is more stable
overall today with the southwest flow bringing in a marine layer.
In spite of this marine layer, inland areas of the Kenai
Peninsula will likely see some more convection this afternoon
though it is questionable whether it will have enough lift to
produce thunderstorms as have been seen the past few days.

&&

.MODEL DISCUSSION...
Models remain in good agreement through the first half of next
week.

&&

.AVIATION...
PANC...The SE winds associated with the Turnagain Arm wind will
slowly diminish late evening through the overnight hours. As this
wind diminishes a moist low-level marine layer pushes up Cook
Inlet from the SW and will move over the airport early tomorrow
morning. The big uncertainty is whether there will be stratus that
develops around the terminal when this happens. Going with some
MVFR ceilings late tonight with this push of marine air.

&&

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

There is some unstable air in place over portions of Southcentral.
Early this afternoon lightning strikes were detected over the Copper
River Basin and the radar at Kenai (PAHG) was detecting showers
near Willow. The convective initiation is being driven by diurnal
heating. More pleasant temperatures are expected the next two
days but with cloud coverage lingering from previous thunderstorms
and the marine layer moving up Cook Inlet, the temperatures will
be a couple of degrees cooler. There is a low south of the AKPEN
that will shift the ridge eastward and this will impact the
intensity and the reach of the thermal troughs that form at the
surface in the valleys.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
(Tonight through Tuesday evening)

Another active day with thunderstorm development is underway. The
Bethel Doppler Radar has even been picking up returns of 50 dbz or
higher as far east as Sleetmute and as far southeast as near
Dillingham, which is impressive considering that radar beam, even
on the lowest elevation slice, is reaching the storms between
20,000 and 25,000 feet. Cross sections have shown that these tops
are likely producing some small hail. These showers and
thunderstorms will continue through the mid to late evening,
before they start to diminish in coverage. The recent wetting
rains combined with light winds and decreasing clouds will help
foster fog development overnight, and this was added to the
forecast for Sunday morning. Fog was also added for the Alaska
Peninsula, where persistent onshore flow and light winds has been
producing morning visibility reductions.

A repeat convective scenario is expected for Sunday and Monday,
perhaps growing in coverage as instability builds westward due to
an increasingly strong thermal trough, while also getting periodic
boosts of ascent as various disturbances aloft cross the region.
As is typically the case, the best chance of seeing storms will be
east of the Kilbuck Mountains. However, instability will build
westward a little bit each day for Sunday and Monday, perhaps
reaching the Bethel area.

As for temperatures, look for seasonably warm temperatures to
continue through the period, with morning fog likely developing in
the valleys and low lying area of the interior, especially if that
location happens to receive any additional rainfall.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
(Tonight through Tuesday evening)

A ridge of high pressure extends south from eastern Siberia into
the western Bering, and this is keeping a frontal system at bay
west of Shemya, as it bumps into this ridge. Anticyclonic
northerly flow and onshore winds has been producing a fair amount
of morning fog for portions of the Alaska Peninsula the past
couple of mornings, and this will continue overnight. Otherwise,
look for a few showers to affect the far western Aleutians, with
dry conditions continuing for the remainder of the Bering Sea and
Aleutians.

&&

.MARINE (Days 3 through 5)...
A gale force low from the North Pacific moves a front across the
western Aleutians early Monday morning. The front pushes across
the western Bering during the afternoon and remains stationary
through Monday night. This system takes an eastward track Tuesday
morning with small craft winds for area marines as the low
slowly weakens through Wednesday. The center tracks just south of
Adak and the eastern Aleutians on Thursday. Models are in good
agreement on the strength and track of this system.

&&

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

The forecast Tuesday through Saturday will be a relatively
persistent across the southern mainland with afternoon showers
each afternoon and evening. The chance for thunderstorms focuses
mainly along a thermal trough that stretches along or near the
Alaska Range for next week. A North Pacific low moves up to the
Gulf on Tuesday bringing light rain through Wednesday, then a
ridge follows in its wake. The next front moves to the Gulf early
Friday taking a similar path to the northern waters on Saturday.

To the west across the Bering...A gale force front with its low
just south of Shemya on Tuesday...weakens on an eastward track
with the low center tracking south of the Aleutian Chain through
Thursday. On Thursday afternoon, the low center is expected to
lift toward the Alaska Peninsula with the frontal boundary pushing
across the southern mainland. Models are generally in good
agreement with timing and strength of this front...however there
is still some uncertainty. A blend toward the operational models
and their ensembles were used to update the afternoon package
which begins to advertise higher chances for widespread rain
heading into the end of next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...KH