Area Forecast Discussion
Issued by NWS Anchorage, AK
FXAK68 PAFC 201258
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
458 AM AKDT MON JUN 20 2016
.ANALYSIS AND UPPER LEVELS...
There is an upper level trough over the Southwest Alaska extending
into the interior. This is reflected at the surface with a trough
over the aforementioned region, and a weak low located in the
northern Gulf. The radar imagery is showing a large swath of
stratiform rain with onshore flow through the northern Gulf
coastal communities. This is associated with the low pressure
system entering the northern Gulf, and the weather front tracking
into the Southeast Panhandle this morning. The satellite imagery
is showing a large swath of moisture streaming from the eastern
Gulf northward into the Yukon Territory. While, upstream there is
a ridge of high pressure over the central Gulf extending through
the Central Aleutians. The satellite imagery is showing marine
layer stratus with this high pressure in the Bering being trapped
under the subsidence inversion. The Scatterometer Wind imagery is
displaying southwesterly flow through the majority of the Bering,
except weak northerly flow in the northern Bering.
The models continue in decent agreement as the next North Pacific
Low tracks into the Western Aleutians by late Monday evening.
This system then tracks into the Kuskokwim Bay region by Thursday
before moving inland. While, the weak low in the northern Gulf
tracks towards the Panhandle before dissipating by Tuesday. The
forecast confidence remains average as we start the work week.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A long wave trough moves east across Southcentral and the Gulf
this afternoon with a clearly defined upper low center moving into
the North Gulf. This center moves southeast overnight as ridging
builds across the Western Gulf/Cook inlet/Susitna valley. Weak
upper waves moving southeast across the interior flatten the
ridge some as they move across Southcentral through Tuesday night.
With the exception of the North Gulf Coast, showery conditions
are expected across Southcentral today with the potential for
thunderstorms along the Talkeetna Mountains and the Copper River
Basin this afternoon. Drier conditions are expected on Tuesday
though upper waves moving southeast across the region could
trigger showers, mainly in upslope areas inland. There is even an
outside chance of thunderstorms over the Copper River Basin
Tuesday afternoon. Outflow winds with low pressure in the Gulf and
generally higher pressure inland will develop across the Eastern
Kenai and North Gulf coast tonight and continue into Tuesday
night. This will give rise to fairly warm afternoon temperatures
Tuesday as seabreezes in these areas will be delayed.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A couplet of upper level shortwave troughs will move east today,
with rain and showers favoring Bristol Bay and inland locations
closer to the Alaska/Aleutian Ranges. Onshore flow will also
support patchy fog, especially along the coastlines. Tonight, the
trough moves east with northwest flow aloft, with a drying trend.
Tuesday and Wednesday will see warming temperatures as a ridge
aloft builds overhead.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Upper level ridging will continue to build over the Central and
Eastern Bering Sea as a North Pacific trough deepens and moves a
warm front into the Western and Central Aleutians Monday night and
Tuesday. This front will be rather elongated, keeping energy
spread out and below gale force.
.LONG TERM FORECAST (Days 3 through 7)...
By Wednesday, the overall pattern will begin to gradually shift
over to a more dry and slightly warmer offshore flow pattern for
Southcentral, as the upper level trough over the gulf shifts
further eastward and ridging builds in over the Southern Mainland
behind it. On the western periphery of the ridge however, the
pattern will switch to an onshore flow over the Western coast.
This will bring more stable conditions and the potential for fog
to form over parts of the Kuskokwim Delta and Bristol Bay area
heading into Wednesday.
Models remain in good agreement through the midweek, then begin
to struggle with the track of a front and its associated low
crossing the Western/Central Aleutians before entering into the
Eastern Bering by Thursday. The models do hint at this system
transitioning to the Gulf by the end of the week, but the lack of
details on timing and positioning will keep forecast confidence
lower for the time being. The end result will likely be rain and
showers to much of the Aleutians and Bering, and diminishing
shower activity to the mainland through Thursday. From Thursday
into the weekend, Rain and showers will move back into the
Southern Mainland from West to East, as the weakening Bering low
pushes eastward and inland over the area through Saturday morning.
SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA