Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 131228
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 AM AKDT Thu Jun 13 2019

.ANALYSIS AND UPPER LEVELS...

This morning`s array of various data sets shows a Rex Block
pattern continuing to hold, with a strong area of high pressure
located over eastern Siberia, and a strong mid-level low centered
well south of Dutch Harbor. This type of pattern occurs when an
area of low pressure gets trapped under an area of high pressure
to its north. It acts as a blocking pattern, allowing for little
change in the synoptic pattern.

A couple of weaker lows were retrograding (moving from east to
west...versus the usual opposite direction) across the northern
and western Bering Sea. To their east, a thermal trough extended
from central Alaska into the Kuskokwim Delta.

&&

.MODEL DISCUSSION...

The models remain in good agreement through the weekend, before
things start to go awry in their continuity for the start of next
week. This is likely the result in their difficulty handling a
pattern change, as the guidance indicates a low moving into the
Gulf, with some degree of interaction with another low centered
over the Arctic waters north of the Yukon.

As this occurs, the Rex Block currently in place over eastern
Siberia and the west central Aleutians gets knocked down, due to a
low over the Sea of Okhotsk that absorbs a shortwave trough from
eastern China. As this occurs, the Okhotsk low deepens while
lifting north into east central Siberia, creating a high amplitude
shortwave ridge from the Chukchi Sea to the western Aleutians
near Shemya.

Bottom line, the numerical models will continue to struggle in all
likelihood until the upstream lows move ashore and gets sampled
by the upper air network of our international colleagues to the
west. As such, a low confidence forecast for the early to middle
portions of next week is in place, with changes likely in the
coming days.

&&

.AVIATION...
PANC...Look for VFR conditions with light winds to persist through
the next 24 hours.

&&

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

Today`s weather pattern is very similar to yesterday with a weak
500 mb trough over Southcentral Alaska which is helping to keep
some mid level clouds over much of the region. These clouds should
lessen this afternoon and some showers will pop up again mainly
over mountainous terrain. The Copper River Basin is the area most
likely to see thunderstorm activity today though the entirety of
the Talkeetna Mountains is also under unstable enough air for
thunderstorms to occur.

The atmosphere becomes a bit more stable tomorrow with
Thunderstorm potential just remaining over the Northern Copper
River Basin and northern portion of the Talkeetna Mountains. This
is mostly due to a front approaching the north Gulf coast and
bringing in a more stable airmass to the region for Friday and
Saturday. As this front approaches it will increase the gap winds
on Friday for the typically gusty areas such as Turnagain Arm and
along the Copper River.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA...

A surface high will gradually build in over Southwest from the
east, providing generally warmer and drier conditions today.
Showers and isolated thunderstorms are possible over the Middle
Kuskokwim Valley and interior areas of the Kuskokwim Delta this
afternoon. A front associated with a North Pacific low will lift
over the Alaska Peninsula and move inland over Southwest for
Saturday, spreading in showers along the southern Alaska Range.
The Bristol Bay and Kuskokwim Delta coast areas should remain dry
due to down-sloping, though an occasional passing shower cannot be
ruled out Saturday afternoon.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS...

Low pressure centered south of the central Aleutians will lift a
front over the eastern Aleutians today bringing cloud cover, rain,
and southeasterly flow. As the low moves eastward toward the Gulf
for the weekend, the rain will taper but cloudy skies will
persist. Meanwhile, high pressure in place over the western
Bering is keeping things relatively dry and calm.

&&

.MARINE (Days 3 through 5)...

On Friday...a surface low slowly tracks eastward just south of the
Alaska Peninsula and then becomes stationary on Saturday. Another
surface low quickly develops across the North Pacific on Saturday
night and take a northward track to the Gulf. This second low will
be the system to watch for gale strength winds. Models are not in
good agreement on the track or strength of this system which could
bring gusty winds as far west as the Alaska Peninsula and across
much of the Gulf.

&&

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

The long range forecast starting on Sunday continues to advertise
higher rain chances across the Gulf as an upper low pressure
system continues to spin near the western gulf. A few showers are
expected to push inland across the southern mainland with upper
level shortwaves rotating around the parent low. To the west...a
ridge builds across the Bering bringing low clouds and fog for the
start of the new week. A front moves toward the western Aleutian
Chain Tuesday into Wednesday, but there is still a bit of
uncertainty on how quickly the Bering ridge breaks down. Overall,
there is high uncertainty between the operational models and the
ensembles next Monday through Wednesday. The forecast was updated
toward the new blends which keeps a clouds and scattered showers
across the southern mainland and surrounding waters.

&&


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

&&

$$

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


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