Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 230051

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 PM AKDT WED JUN 22 2016

There is an upper level ridge over southern Alaska with the axis
running from Kodiak Island north through McGrath. There is an
upper level low over the central and eastern Bering Sea. High
clouds extend westward from the ridge axis, with slowly lowering
ceilings into the Bering. There is an upper level low over
northeast Alaska, with some cyclonic flow just clipping the
northern Copper River Basin. Convection is fairly suppressed
today with the ridge overhead.


The numerical models are in good agreement through the short term
(Friday afternoon). There are some very minor differences with
precipitation and convection. The models have come into excellent
agreement with the surface low as it drops into the Gulf near
Kodiak Island on Friday. For these reasons, forecast confidence
is above normal today.


Upper level ridging over the area is allowing for clear skies and
temperatures into the 70s for many locations around Southcentral
Alaska. The ridging will break down overnight but there will still
be enough clearing early Thursday for temperatures to reach the
mid 70s for interior locations like the Susitna Valley and the
Copper River Basin. There will be enough mid and high clouds
around to keep RH values above 30 percent for most areas. The
exception is the Copper River Basin which will see RH values
drop into the mid to upper 20s Thursday afternoon.

This puts the Copper River Basin close to critical fire weather
thresholds for temperatures and RH values. The more difficult
parameter to forecast is winds. A Ridge will build along the
North Gulf coast Thursday as a weak front enters the southwest
Gulf. Pressure gradients are fairly weak for this very common
pattern, but it looks like just enough gradient to produce gusty
southeast winds along the Copper River. The strongest winds will
likely hold off until the evening hours and thus will not
coincide with the maximum temps and minimum RH in the Copper
Basin. Still, it will be very close to meeting Red Flag Criteria.
Thus, have coordinated with AICC to issue a Red Flag Warning.

Widespread clouds and increasing chances of rain will return
to Southcentral Thursday night and Friday as a weak surface
front and broad upper level trough pushes into the region from
Bering Sea.


.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...thu and fri)...
A pattern change is underway. The ridge that brought the warm and
dry conditions over the past couple of days is being pushed off
to the east by a broad area of low pressure. This low is
currently centered over the Central Bering and its initial front
already moved onshore bringing some very light rain to the Alaska
mainland. As the low tracks east it will bring a much cooler
maritime airmass with it. This means abundant cloud cover and
increasing stability for just about all areas. As for rain
chances, it is going to depend on timing. As the low moves
onshore Thursday it will also be falling apart. this means the
precipitation might not be very focused in nature, but instead
more of a showery scenario. The exception to this will be along
the coast late tonight into early Thursday where a tenth or so of
rain is certainly possible.

As the low does fall apart over the will not be strong
enough to push the marine airmass all the way into the Alaska
Range. Thus, with some sunshine near the surface and generally
cool temperatures aloft some isolated garden variety thunderstorms
will be possible. Instability will increase in this area on Friday
bringing an even better chance for some thunderstorms.


The broad area of low pressure will slide into the Alaska mainland
on Thursday while a ridge builds over the Western Bering. this
will leave the Eastern Bering in northwest flow. This makes areas
like Dutch Harbor and the north side of the Alaska Peninsula
vulnerable to waves of energy from the Arctic. These often times
can bring heavier rain and gusty winds. Models are hinting at one
such wave for these areas early Friday. We will continue to fine-tune
the forecast as these pieces of energy are rather hard to nail down.

Meanwhile, the ridge over the Western Bering will bring widespread
marine stratus and fog for the next few days. Westerly flow will
become generally light and variable by late Friday.


.LONG TERM FORECAST (Days 3 through 7)...
The long range pattern will continue the progressive movement of
the upper level systems traversing Alaska into the weekend,
followed by a slowing of the pattern to start off the upcoming
work week. A high amplitude ridge will build over much of the
Bering Saturday. By the weekend, the upper low over the Gulf will
stall out there as it runs into the semi-permanent upper level
ridge over the Canadian Rockies, which in turn will halt the
eastward movement of the Bering ridge. For Southcentral, this
pattern evolution will favor one with convection and precipitation
potential on most days, especially on Saturday as the low passes
by. This potential will also persist through early next week for
coastal locations along the Gulf and Kodiak Island. The driest
weather throughout the Saturday through Tuesday time frame will be
towards the Alaska Range. For the Southwest Mainland, dry and warm
conditions are expected as the upper ridge builds in through
Tuesday. Over the Bering, the persistent upper ridge will promote
an environment favorable to the development of widespread fog and
low stratus through the weekend. The next organized weather
system will enter the western Bering late Sunday into Monday
morning, bringing unsettled weather back to the area. It will
move through the Central Bering by Tuesday.

Ample daytime heating over interior Alaska along with the
movement of the next upper level trough over Eastern Russia will
help push the northern portion of the Bering ridge over mainland
Alaska next week. The southern portion of the ridge will remain
stuck west of the stalled out upper low over the Gulf, effectively
making the ridge positively tilted. Beyond that, the models are
now trying to keep the cut-off upper low rotating around the gulf
through the middle of next week, which seems to phase with a
disturbance in the polar jet. There is still some disagreement
between the models regarding the finer details and evolution of
this feature, which has resulted in lower forecast confidence
for the middle of next week.





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