Area Forecast Discussion
Issued by NWS Anchorage, AK

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622
FXAK68 PAFC 281223
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 AM AKDT SUN AUG 28 2016

.ANALYSIS AND UPPER LEVELS...
Very little overall change has occurred in the weather over the
last 24 hours. A series of waves continue to rotate around a broad
upper level trough stretching from the Eastern Gulf into the Yukon
Territory are bringing areas of mid-high level cloud cover to the
South Mainland. This is however occurring under dry northerly
flow, so very little in the way of precipitation or low level
moisture is associated with them. Under this trough, weak low
pressure over the Gulf continues to bring gusty outflow/offshore
winds to much of the Gulf Coast and Southcentral. This allowed
temperatures to rise well into the 70`s Saturday evening, setting
record highs at many locations (including Anchorage). Over the
Bering, a weak low continues to slowly spin south of the Central
Aleutians, bringing showers and moist southerly flow to much of
the region. This moist flow is also producing widespread
fog/stratus over the Bering as it moves into the ridging over the
Northern and Eastern Bering.

&&

.MODEL DISCUSSION...
The models remain in very good synoptic agreement as weak flow
aloft persists into early next week. As a result the higher
resolution NAM/WRF-ARW was used heavily again tonight, especially
to fine tune the outflow winds over the Gulf Coast. Over the Aleutians
there remains some minor disagreement with the low track of the
complex low just south of Adak, however this low will stay largely
south of the AOR and not have a significant impact on forecast
confidence.

&&

.AVIATION...
PANC...The main challenge today will be the timing and strength
of the N-NE winds that will persist for most of the day. ACARS
data overnight and the 12z Anchorage sounding indicated NE winds
to 25 kt at 2000 ft, so if the N winds at the SFC diminish early
this morning there may be isolated areas of LLWS. This should
however should be brief as the SFC winds increase again with
daytime heating. Otherwise conditions will remain VFR into Monday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Dry northerly flow will continue over south central Alaska through
Monday night. The only area with any chance of precipitation is
over the Copper River basin, where slightly cyclonic flow aloft
will contribute to some isolated showers today. Then the flow
will become more neutral or even anti-cyclonic tonight. The main
forecast challenge is the the strength of the offshore winds,
especially in such areas as Valdez, Whittier, and Seward where the
offshore winds tend to be the strongest. Temperatures will also
continue to be well above normal over much of the area due to the
high 500 mb heights (warm atmosphere), abundant sunshine, and
downslope/offshore winds.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure currently centered over the Kuskokwim Delta coast
will continue to shift west into the Eastern Bering this morning,
allowing for more northerly offshore flow to become dominant. This
will allow for continued dry and warm conditions through Tuesday.
Ample solar heating will also allow for increased afternoon
gustiness with the northerly winds. The potential for some fog
remains an issue along the Kuskokwim Delta this morning, as the
northerly winds may decouple inland while marine air remains near
the coast.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A rather weak but sprawling low over the North Pacific centered
south of Adak will continue to lift a weak warm front northward
into the central/eastern Bering Sea and Pribilof Islands today.
This will bring some light rain and patchy fog to these areas.
The low will slowly drift northwest with lobes of energy rotating
around the low. This will keep periodic light rain and
southeasterly winds across most of the Bering through Monday
night. Overnight Monday into Tuesday, the low will redevelop and
push northward, with another front lifting northward into the
Central/Eastern Aleutians and Bering. this will bring another
round or rain and gusty winds to the area for the mid-week time
frame.

&&

.LONG TERM FORECAST (Days 3 through 7)...
At the start of the long term forecast on Monday night, the most
active weather pattern will be along the western areas of the
Bering and Aleutians where a front moves up from the North
Pacific. Small craft southeasterly winds are expected to accompany
this front along with rain. The surface low that pushes the front
moves to the central Aleutians and stalls Tuesday through
Wednesday. The boundary slows in response across the western
Alaska Peninsula to the northern Bering.

A ridge remains to the east of this system through mid week while
low pressure from the Yukon begins to track toward the northern
gulf. The ridge will keep the southern mainland in a drier pattern
through much of the week with offshore flow bringing gusty
conditions across channeled terrain. The main forecast challenge
across Southcentral into mid week will be how far east the Yukon
low tracks before it moves into the gulf. Models have been
trending this system further west with each run, however they
continue to stay in agreement that precipitation stays confined to
the mountains of the eastern Copper River Valley. Thunderstorms
are not currently expected with this system, however there may be
enough instability to initiate isolated activity along the
northeast gulf as the upper cold core low dives into the gulf over
an inverted surface trough extending from the eastern gulf.

There is higher uncertainty in the forecast heading into the end
of the work week as models struggle with handling several closed
systems. The Bering storm system is the main focus for this time
frame with an eastward track anticipated. This stalled system,
along the Western Aleutians on Wednesday, is expected to be
kicked eastward as a closed low dives south over the Kamchatka
Peninsula and merges into one eastward moving system. Despite the
lack of model run consistency, all operational trends show an
organizing system pushing a front into eastern Bering on Friday,
possibly leading to a wetter weekend for the southern mainland.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

SYNOPSIS, MODEL DISCUSSION and AVIATION...DEK
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KH



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