Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 280145

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
545 PM AKDT Tue Jun 27 2017

Water vapor satellite imagery shows an organized upper level low
spinning over the southern Bering this afternoon. A long fetch of
subtropical moisture is riding up through the gulf between the low
in the Bering and weak ridging along the eastern Gulf. A swath of
rain developed this afternoon along the re-enforced surface front
with the boundary extending from the the southern Cook inlet
across to Middleton Island. East to southeast flow is increasing
this afternoon along the frontal boundary and also along east to
west favored gaps such as Turnagain and Knik Arm. The boundary
across the Southwest mainland is momentarily diffuse with winds
starting to increase along the Aleutian Range. The low centered
over the Bering is splitting the flow with gusty southerly winds
across the eastern waters and lighter west to northwest flow west
of a line from Saint Paul to Dutch Harbor.



Models are in relatively good agreement with the synoptic pattern
through Thursday. The pattern remains dominated by a broad
longwave trough across southern Alaska and the Bering. The closed
low over the Bering slowly shifts northwest and another developing
low in the North Pacific centers just south of Kodiak Thursday
morning on a northerly track.



VFR conditions are expected to prevail through the next TAF
package, however skies will remain overcast with deep southerly
flow advecting moisture inland from the Gulf. Rain developing
along a front over the Kenai picks up momentum spreading rain
across Anchorage through this evening, then tapers off around
midnight. Gusty southerly flow this afternoon increases as the
frontal boundary pushes north and tapers off in it`s wake.
Southeasterly gusts are expected again Wednesday afternoon as the
pressure gradient is squeezed along Turnagain Arm due to a
building ridge across the Northeast Gulf coast.


A front over the Northern Gulf will push further northward into
Southcentral Alaska this evening, bringing another round of rain
and/or showers to the area. The highest rainfall amounts will be
along the coast and coastal mountains. Less precipitation will
fall inland, with only some isolated showers in the the Copper
River basin. The system will move north of the area by late
Wednesday night, with just some showers lingering along the coast
by Wednesday afternoon. The next system will track through the
Gulf Wednesday afternoon, reaching the Gulf coast Wednesday night
into Thursday Morning. This next system will develop into a closed
upper low, and have a defined surface low as well near Kodiak
Island. This will push the flow aloft to come from the southeast
rather than the south, enabling downsloping to occur over the
areas on the lee side of the mountains. Ultimately this will
cause areas along the mountains of the western Kenai and Anchorage
Bowl to be a bit drier in a downsloped regime.

Winds along Turnagain Arm will persist through Thursday,
remaining mainly over the inlet with the exception of a few hours
here and there clipping the southern portions of the Anchorage
bowl. Models are showing tonight as being the best chance for some
gusts to make it into the southern portion of the Anchorage bowl.
From Wednesday morning trough Thursday, the models seem to keep
the gusts mainly over the Arm and even bending down-inlet by



The main challenge will be the coverage and intensity of
precipitation with the front across the southwest mainland and the
subtropical influx of moisture over the next day or two. Strong
cross barrier flow will inhibit the intensity of the rain on the
lee side of the Aleutian Mountains and Alaska Range and conversely
the upslope orographic lift regions will experience mush higher
rainfall amounts. Since the main upper level and surface low
remains anchored over the eastern Bering Sea, we expect troughs
to continue to rotate around this system into the southwest
mainland through tomorrow night. The main longwave upper trough
holds over the Bering Sea through Thursday and will usher in more
moisture across the Aleutian Mountains and Alaska Range from yet
another Gulf of Alaska low.

The only region where wind is of any concern is through Kamishak
Gap into the Lake Iliamna area this evening as a low level jet is
funneling through the gap.



The main surface and upper level low in the main longwave upper
level trough will persist over the eastern Bering Sea for the next
few days. The rotation of troughs around the base of this low will
rapidly move along the central and western Aleutians en route to
the Bering Sea coast. Timing the troughs along the Aleutians will
be the biggest challenge for the forecast along them as rain or
showers and gusty wind associated with the troughs move through.
Along the Alaska Peninsula the persistent onshore flow in the
mostly stable air is resulting in lower clouds and intermittent
light rain or drizzle that should persist through the next day or
two. The lower clouds and drizzle and fog will also persist in the
Pribilof Islands.


.LONG TERM FORECAST (Days 3 through 7)...
The weather pattern for the long term continues to trend towards
wet and rainy for both the Gulf and the Bering Sea. By Sunday, the
lows currently in the Gulf and the low moving into the Bering will
weaken, but strong ridging is not expected to set in and clear
things out. Aloft, by Sunday the jet stream will be in a zonal
pattern through the Gulf of Alaska, with a stronger jet streak
moving southward from the Kamchatka Peninsula into the western
Bering Sea. This pattern will allow for development of some
surface lows which will move eastward into the Gulf of AK and
southward from Russia into the Bering Sea. These low pressure
systems are not expected to be unseasonably windy, but will bring
low clouds and rain to most of the region, with some land areas
perhaps getting a short break with downsloping. Although all the
models agree on a generally unstable pattern, the timing and
strength of lows moving into the Bering and the Gulf vary quite a
bit. Therefore, the current forecast trends toward little change
with some blend of the WPC solution, especially as we head into
Day 7 and 8. All in all, the outlook for 4th of July weekend
across the southern mainland and Aleutians is rather cloudy and





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