Small Craft Advisory 512, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
417 PM AKDT Mon Jun 29 2020

.ANALYSIS AND UPPER LEVELS...

A frontal boundary extends from a low over eastern Russia to over
Southwest Alaska then west over the Bering Sea. Showers are
focused along and head of this front, which is pushing up against
the Alaska and Aleutian Ranges. The leading edge of the upper
trough is pushing eastward into Southcentral Alaska. Deep
southwesterly flow up Cook Inlet and the Susitna Valley is leading
to some upslope flow as well. The end result is cloudy skies and
showers across much of the Mat-Su. Meanwhile, out west a
deepening low southwest of the Aleutians is sending a a gale
force frontal system toward the western Aleutians. Winds and rain
are on the increase.

Clear skies dominate the northern to eastern Bering Sea and into
the Kuskokwim Delta, while a broad area of stratus and fog
stretches across the remainder of the Bering Sea and Aleutians.

&&

.MODEL DISCUSSION...

Models overall are in fair synoptic agreement through the short
term. Minor differences in QPF/POP fields out west will be
handled with model blends.

&&

.AVIATION...

PANC...VFR conditions will persist. There could be some brief
gusty winds off the Inlet late this afternoon into evening.
Otherwise, winds will diminish tonight and persist through
Tuesday.

&&

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

An upper level trough in place over the northwestern Mainland may
allow for a few shortwaves to cross over the northern part of
Southcentral this afternoon and evening. This will bring a chance
for showers across the Susitna Valley and northern Copper River
Basin. Southcentral will then see a pattern change with a ridge of
high pressure moving overhead beginning Tuesday, allowing for
improving conditions through the rest of the week. Mid-level
winds will bring plenty of offshore flow allowing for a warming
and drying pattern. High temperatures on Thursday could approach
the mid 70s across interior locations while areas along the coast
will remain slightly cooler in the upper 60s.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Monday
night through Thursday)...

A frontal system continues to push through Southwest Alaska.
Coastal areas, especially the Y-K Delta are clearing behind the
front, while cloud cover is hung up against the Alaska Range to
the east. Post frontal flow off the Bering Sea is also keeping
temperatures cool for Southwest Alaska. Ridging will build in
starting tomorrow, with the ridge at its apex over the region on
Wednesday. This will keep weather calm and warm temperatures into
midweek, especially for interior areas of Southwest Alaska. So,
upped maximum temperatures to reflect that trend. Models fall
apart on Thursday so it's tough to tell what will happen later in
the week, though there is enough to show that the ridge shifts
east and southwest flow enters. This signals cooler, cloudier
weather and an increased chance of precipitation Thursday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Monday night through Thursday)...

Mainly zonal flow exists for the Bering Sea, with the tail end of
the recently passed front stretched along the eastern Aleutians.
As usual, most of the Bering is under low to mid level cloud
cover. Satellite imagery shows the cirrus shield of the next
system just entering the western Aleutians. The forecast for this
system to track across the Bering the next few days is on track.
One update today is an increase in wind speed as models are
consistent today in showing gale force winds with the front. So,
updated the forecast to have a solid swath of gales with this
front. The front does weaken as it progresses so gales will be
present until Wednesday morning, at which the front is expected to
be in the Central Bering. Thursday the front will be in the eastern
Bering with winds falling below small craft advisory by that time.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

A surface low moves into the western Bering Sea Thursday
night/Friday and becomes stationary and slowly weakens through
Saturday. Winds are expected to hold in the small craft range with
this system. However, it is possible that there could be low end
southerly gales over the central Aleutians/Bering Sea with the
front on Friday. Quiet conditions will persist across the Gulf
waters.

&&

LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

A blocking upper ridge sets up over the Gulf and the Mainland
with troughing over the Bering Sea/Aleutians during the later
part of this week and should persist into Monday. However, models
do differ some on the strength and location of the ridge axis.
That said, there is enough confidence to go with generally warmer
and drier conditions across much of the Mainland. Exceptions may
occur though. If the ridge is a little further east it would allow
the trough over the Bering Sea to spread a moisture and cooler
temperatures into coastal Southwest Alaska. Also, A few models are
dropping upper short waves south across the eastern Interior/
Copper River Basin through the period which will bring the
possibility of increased clouds and shower potential to these
areas.

Troughing over the Bering Sea/Aleutians will keep the area under
generally cloudy conditions with periods of wind and rain/showers
through Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 173 175 176 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CB/BC
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BB
MARINE/LONG TERM...BC