Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 210049
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Wed Jun 20 2018

.ANALYSIS AND UPPER LEVELS...

The overall pattern remains very similar to the previous few days
but there is a small change that is causing a change in the
forecast over Southcentral. The main items of interest today are
all impacted by the upper level ridge that is in Canada and
pushing into the interior of the state. The ridge appears to be a
bit stronger than was expected and that is impacting the movement
of the front in the Gulf of Alaska (more information on specifics
of this front in the model discussion section below). This ridge
is also bringing in warmer temperatures to much of Southcentral
Alaska today.

Weak instability remains over the Kuskokwim Delta and in the
northern Copper River Basin this afternoon.

&&

.MODEL DISCUSSION...
It can be stated once again that models are in good agreement in
the overall synoptic pattern. However, the models from yesterday
show once again that model consensus does not necessarily mean
correctness, as there are some significant shifts in the forecast
solutions for tonight through Friday across Southcentral and
parts of Southwest Mainland Alaska. In short, the upper level
ridge poking into the interior of the state from Canada is
stronger than any models were indicating yesterday. This is
slowing the progression of the front that is in the southwest Gulf
of Alaska and delaying it by 12 to 24 hours. In addition the
front will be weaker and bring less precipitation to Southcentral
Alaska, though it will move across Kodiak and the Bristol Bay
regions slower and therefore bring more rain to those areas.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The pattern of an upper level low over the Bering and ridging to
the east of Southcentral Alaska will continue through the end of
the week. However, this pattern will start to break down on
Friday. Flow aloft will still be out of the south bringing more
moisture to the area and a shortwave moving through the flow is
supporting a surface front moving through Kodiak Island. The front
will make it over the Kenai Peninsula Thursday spreading more
rain and cloud cover to the area. It will then break apart but
will bring showers to areas around Southcentral Alaska. Showers
and weak flow will continue into Saturday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The broad elongated upper level low stretching across the eastern
Bering, Bristol Bay and Alaska Peninsula will gradually broaden
through Thursday and then begin drifting slowly northwest on
Friday. A frontal wave pushing across the area from the southeast
to northwest will bring quite a bit of rain overnight with QPF
amounts of a half to three quarters of an inch of rain under the
center of the wave and totals of two tenths to four tenths of an
inch along the periphery. Showery weather will continue on
Thursday with a secondary peak in coverage in the afternoon and
evening then taper off to more of an isolated to scattered
coverage on Friday as the upper low begins to move away. Isolated
thunderstorms will be possible in small portions of the forecast
area each afternoon and evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The upper level low in the eastern Bering will remain the primary
weather feature tonight through Friday as it broadens and shifts
gradually west into the central Bering. A Pacific frontal system
will reach the western Aleutians Friday night and central
Aleutians Saturday.

&&

.LONG TERM FORECAST (Days 4 through 8)...

Models continue to be in good agreement with the overall synoptic
pattern through the long term, especially over the northern Gulf
and southcentral Alaska. A low in the northeast Pacific will
continue its trek toward the Alaska Panhandle for the weekend as a
ridge of high pressure slides into the northern Gulf. Over the
interior, a thermal trough will set up roughly along the Alaska
Range as an upper-level ridge retreats northward. This will also
establish a weak offshore flow, allowing for a general warming
trend across southern Alaska. A series of upper-level shortwaves
will move across southern Alaska around both the cyclonic
circulation over the Bering and the low over the Alaska Panhandle.
This will aid in the instability and result in scattered afternoon
and evening clouds and showers throughout southern Alaska. The
ridge begins to break down Tuesday as the next low advances from
the west.

Over the Bering, the occluded low will continue to slowly break
down and retreat to the northwest as high pressure spreads across
southwest Alaska over the weekend. The weak, cyclonic flow aloft,
however, will still provide enough moisture and instability for
the build-up of late day clouds and showers across interior
locations. A low moving into the southern Bering from the western
Aleutians on Sunday will help reestablish the upper-level low
across the region. This trough will slide east back over the
eastern Bering on Monday a surface low tracks toward the AKpen for
Tuesday. There is still uncertainty in the timing and placement
of the surface low and its upper-level companion with the GFS
favoring a more progressive solution over the EC. GFS placement
of the trough axis is also negatively tilted and farther south
than the EC, bringing more moisture into southwest Alaska by late
Monday. Nonetheless, the developing pattern favors unsettled
weather returning to the Bering and Aleutians by the start of next
week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 145.
MARINE...None.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...TM



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