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fxak68 pafc 261120 

Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
320 am akdt Wed Apr 26 2017

Analysis and upper levels...

It's about as close as it gets to a copy paste setup in the
weather this morning as compared to yesterday morning. The
vertically stacked low over the central Aleutians has only drifted
a short distance north, and it continues to be driving the
steering flow. The primary differences from yesterday revolve
around small scale features moving in the flow. For the whole of
southern Mainland Alaska, the steering flow is approximately
southeasterly. This means moisture is being advected from off the
Gulf into much of the southern half of the state.

With the stacked low over the Aleutians weakening with time, the
steering flow has weakened considerably from yesterday. The result
of this weakening is the end of downsloping across southcentral.
Not surprisingly, the latest Anchorage sounding supports that,
being nearly saturated from ground to tropopause. So why aren't
all areas being soaked? It's all about the forcing, which in this
instance is weak. So as weak waves of energy move through the
flow, the shower activity is locally enhanced for a few hours,
then for the most part returns back to occasional sprinkles.

Over southwest Alaska, a similar story holds true, with more
organized shower activity exiting the Kuskokwim Delta out towards
the Bering. Otherwise, much of the area is seeing cloudy skies
with showers off-and-on from time to time. For the Bering, the
counterclockwise flow around the low is resulting in the shower
activity moving up from the southwest over the eastern Aleutians,
and from the north over the western Aleutians, but regardless of
the origins of the shower activity, the pattern is the same.


Model discussion...

Like yesterday, the models remain in excellent agreement through
the short-term as the low over the Bering continues to weaken for
the next couple days. The models also largely agree on the advance
of the next front into the western Aleutians Thursday. As with
yesterday, the challenges remain timing any shower activity in any
one location in southern Alaska, though wind concerns have reduced
considerably due to weak broad-scale flow. The NAM was the model
of choice, but any of the models could've been used as they all
are in agreement. Forecast confidence is high.



Panc...VFR conditions with occasional sprinkles and light winds
will persist.


Short term forecast southcentral Alaska (days 1 and 2)...

Mostly cloudy conditions will persist Wednesday and Thursday with
the possibility for rain showers along the mountains. The
stagnant upper level flow pattern continues with very little in
terms of dynamic forcing for the next couple of days. Light
southeasterly flow aloft will keep a steady stream of moisture and
clouds from the Gulf of Alaska. With little to focus this
moisture, the only precipitation chances will come from diurnal
instability. The combination of Spring temperatures in the low
levels and still seasonably cold upper levels will give rise to
isolated to scattered showers in the afternoon/evening hours,
mainly along and over higher terrain. High temperatures will be
near 50 degrees with low temperatures in the mid-upper 30's. Winds
will remain generally light through the period.


Short term forecast southwest Alaska (days 1 and 2)...

A low pressure system over the southern Bering will send a series
of weak waves across the southwest Mainland and Alaska Peninsula
through Friday. This persistent pattern will continue to produce
widespread showery conditions and southerly flow over much of the
area through the end of the week.


Short term forecast Bering Sea/Aleutians (days 1 and 2)...

A low pressure system over the southern Bering weakens into an
open wave on Thursday, and then drifts slowly into the eastern
Bering before dissipating on Friday. This system will continue to
produce showery conditions over much of the Bering, along with
some gusty northerly winds mainly over the western Aleutians
through Thursday.

The next frontal system stems off of a low over southern
Kamchatka, and begins to track over the western Aleutians by
Thursday evening. This system will bring rain and gusty gale
force winds along the front, which will then slowly track into
the central Aleutians/Bering by Friday.


Long term forecast (days 3 through 7)...

The long-term forecast (this weekend and early next week) looks
like a continuation of the rather cloudy pattern that has spread
across much of Mainland Alaska. The current stationary low in the
central Bering will weaken and move to the southeast over the next
few days, but by the weekend it will be replaced by a renewed low
pressure system moving through the Bering and parking near the
akpen or Kodiak Island. The models have been struggling with where
this 2nd low will set up shop...and the final position will be
the difference between continued cloudy with occasional showers at
inland locations, or thick clouds with steady rain for many
areas. For now, the more showery solution is preferred, as it
shows a bit more run-to-run consistency and also is supported
heavily by climatology. This should mean near or slightly above
normal temperatures continuing over southcentral Alaska, and
above-normal over southwest Alaska.


Afc watches/warnings/advisories...
Fire weather...none.



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