Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 121233

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 AM AKDT Tue Jun 12 2018

Most of the action this morning is focused over Southcentral and
eastern portions of the state as a deep upper trough originating
from the Arctic continues to bring unseasonably cool and wet
conditions to the area. This system brought impressive
precipitation amounts to Southcentral yesterday with 1.22 inches
of rain falling in Gulkana, which ranks it as the 2nd highest
precip amount for the whole month of June, which fell over only a
24 hour period! Additionally, 4-5" of rain fell near Cordova and
up to 8 inches of snow fell in Eureka. Currently, the upper trough
axis lies right over Southcentral and is slowly pushing east.
Radar shows a broad area of moderate to heavy rain over the Gulf
Coast being enhanced by persistent southerly on-shore flow.
Showers are beginning to wrap up over the Mat-Su/Anchorage areas,
though some showers do remain across Knik Arm.

High pressure with dry northerly flow dominates the southwest
mainland and Bering Sea with clear skies over land and a
widespread area of low stratus and fog seen over the western half
of the Bering Sea and along the northern side of the Aleutians.


Models are in good agreement for most of the forecast period with
good consensus on the exiting arctic trough and the arrival of the
next big system coming up from the North Pacific by Thursday


PANC...VFR conditions will persist through the TAF period.
Turnagain Arm winds are expected to redevelop later this evening,
but should have a more south/southwest orientation with decent up
inlet flow today.



The upper arctic trough which brought abundant rain to
Southcentral Monday continues its slow progress eastward. A
secondary and much weaker upper trough moves south across
Southcentral and merges with arctic trough. The whole system then
heads into the eastern Gulf Wednesday night. These features will
tend to continue the threat of showers and even some isolated
thunderstorms over the Copper River Basin this afternoon and early
evening. Conditions will be more stable with fewer showers on
Wednesday with subsidence on the backside of the trough. At the
surface, generally weak low pressure will continue inland today
with weak ridging along the North Gulf Coast. This will give rise
to gusty easterly  winds across Turnagain Arm and with some
sunshine and heating over the Susitna Valley will draw gusty
southeast winds into south and west Anchorage this afternoon and
early evening. Pressure gradients reverse tonight as low pressure
develops along the North Gulf Coast in response to the upper
trough. This will tend to produce gusty westerly outflow winds
over the eastern Kenai Peninsula/Western Prince William Sound and
gusty north winds across the North Gulf coast tonight into
Wednesday morning. These winds will diminish Wednesday afternoon
with weakening pressure gradients.



In the wake of the recent frontal passage, southwest Alaska
remains in dry and under the influence of northerly flow. At the
onset of this forecast period, southwest is between high pressure
anchored over eastern Russia and an upper-level trough over
eastern Alaska. The arctic vortex will bring another shortwave
into the region later this week. This will be a positive tilted
piece of energy with the upper level heights decreasing late
Wednesday and Thursday. This shortwave will clip the northern
zones of the southwest including the YK Delta and push eastward
before getting absorbed into the longwave pattern. An occluded
front will push across the AKPEN and into southwest late Thursday
and Friday.



High pressure continues to influence much of the Bering. The
latest ASCAT/advanced scatterometer pass has the center of the surface
circulation near NE Russia with broad anticyclonic north of the
chain. Expect this high to persist over the Bering the entire
forecast period. By Thursday, a developing low will move towards
the Central Aleutians from the north Pacific. This system will
rapidly intensify and develop an occlusion. This system will bring
gale force winds and rough seas to the area.


.LONG TERM FORECAST (Days 3 through 7...Thu through Mon)...
The long term will start with much of southern AK caught between
two systems. To the north, the cold Arctic trough continues to
hang on, even in mid-June. Meanwhile, to the south, another
feature that is somewhat rare this time of year will move toward
the southern mainland. It is a fairly potent storm system made
stronger by incorporating the remnants of former Tropical Storm
Maliksi. So for sensible weather, Thu will see a fair amount of
sunshine across the area with another round of afternoon shower
and some isolated thunderstorms. But by early Fri, the extra-
tropical system will bring widespread moderate rain to Southwest
AK. This rain will reach Cook Inlet and the eastern half of
southern AK by Fri evening. We will be watching the associated QPF
amounts for any potential impacts to rivers across the region.

This system will be strong enough to reorient the entire synoptic
pattern allowing a broad trough to establish itself over the
Eastern Bering into Western AK. The result of this longwave
pattern is a much cloudier and wetter pattern than what we saw to
start June. Temperatures will remain rather seasonal, but
afternoon highs will certainly stay (and feel) a bit colder
without the sunshine and morning lows will likely be a bit warmer
with some clouds for isolation. Models due start to diverge (as
usual) later in the forecast with the ECMWF being the most bullish
on the Eastern Bering trough. But none of the models are painting
any sign of a strong ridge bringing hot and dry conditions to the
southern mainland through early next week. Thus, expect fire
weather concerns to remain low.





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