Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 190006
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
406 PM AKDT Sat Aug 18 2018

.ANALYSIS AND UPPER LEVELS...
The main feature remains to be the front associated with the North
Pacific low wrapping over the AKPen and Southwest, which can
easily be seen on IR satellite imagery. Strong winds are
occurring on the backside and in advance of this occluding front
as it moves north and east. These winds and rain are extending
from the AKPen and Bristol Bay to the western Gulf, with over an
inch of rain already recorded at Kodiak City. A 110kt jet
continues to be situated at the base of the trough. A ridge sits
over Southcentral with precipitation drifting northward from the
warm front associated with the low. Ridging sits over the western
Aleutians bringing cirrus to the area as a surface front
approaches from the west.

&&

.MODEL DISCUSSION...
Models are in good agreement with the placement of the front
associated with the North Pacific low as it moves into the Gulf.
The main difference between the models is the QPF totals over the
southern and eastern Kenai Peninsula. The GFS has lower values
through Monday, but then seems to be in better agreement after
that. For this reason, the EC and NAM are the favored models for
QPF totals, particularly over the Seward area.

&&

.AVIATION...
PANC...Generally VFR conditions with some light rain or showers.
Winds will be fairly light at the surface. However, a strong SE
wind aloft will develop overnight and bring LLWS to the airport
complex.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The weak warm front draped over the Southcentral mainland will
continue to move north tonight and dissipate by morning. The next
(and much stronger) front will push across Kodiak tonight, and
reach the Kenai Peninsula in the morning. The front will then
progress northward through the day Sunday. This front will bring
gale-force winds to some of the marine areas, mainly from the
Barren Islands southward, including through Shelikof Strait. Some
gusty winds are also expected along Turnagain Arm.

By Monday the flow aloft will be almost directly from the south.
This will bring a considerable amount of precipitation to coastal
areas and surrounding mountains, with less rainfall inland. There
will be enough rain along the Gulf Coast to raise river and
stream levels late Sunday into early Tuesday. The main concern is
the rivers and streams near Seward, where rainfall is expected to
be in the range of about two and a half to four inches.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A warm front will continue to push through the southwest Mainland
tonight, originating from a north Pacific low tracking eastward
just south of the AKPEN. The Greater Bristol Bay area and some
areas along the Kuskokwim Delta coast will receive the bulk of the
precipitation tonight, then transitioning to the Lower Kuskokwim
Valley through Sunday night. Generally, light rain will spread
over most areas through Monday morning, except for downslope
areas of the Alaska Peninsula/Aleutians.

Along with the spreading precipitation, gusty southeasterly winds
continue to increase tonight and peak during the morning hours
Sunday, especially through gaps along the Alaska and Aleutian
Ranges and along the western capes. The front will stall out
overhead late tonight into Sunday, getting reinforced by a
disturbance aloft and moving it northward during the day. Winds
will drop off pretty quickly Sunday morning behind the front.
Late Sunday into Monday, the area will be left under weaker but
moist cyclonic flow, keeping at least a chance of showers in the
forecast. A stronger disturbance will bring more steady rain
Monday evening into Tuesday. Temperatures will remain right around
climatological normals for this time of year with mostly cloudy
conditions.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Widespread rain and gusty winds will continue over much of the
eastern half of the Bering Sea and Aleutians through Sunday
morning. Wet and windy conditions will briefly diminish Sunday
evening. However, these conditions will quickly be replaced by
showery and much less windier conditions as the next front tracks
in from the west by Monday morning. These conditions will persist
through Tuesday morning under some fairly moist south to
southwesterly flow.

Further west, high pressure over the area will continue to erode
away to the south as the next low pressure system and associated
front track into the area tonight through Tuesday morning. This
secondary warm front will bring another batch of slightly warmer
temperatures, rain, and some gusty winds to the western half of
the Bering and Aleutians through monday morning. The front will
track eastward by monday morning as mentioned above, with the
parent low tracking in behind it over the western/central
Aleutians and Bering through Tuesday morning.

&&

.LONG TERM FORECAST (Wednesday through Saturday)...

The long term forecast begins Wednesday morning with a rapidly
weakening surface low over Eastern Alaska and the Copper River
Basin exiting the state to the east. Showers will taper off
through the morning from west to east as a transitory ridge builds
in behind the low over Southwest and Southcentral Alaska. This
should lead to a brief period of decent weather over the southern
mainland before the next system rolls into the area from the
Bering by Thursday.

A broad low pressure system over the Bering will bring increased
winds and waves with rain showers to most of the Bering/Aleutians
through the later half of next week. A front from this system will
push east across the southern mainland over the Thursday/Friday
timeframe, though details are murky at this time. Model
disagreement and uncertainty begins to creep in by the weekend
with the GFS showing a high amplitude ridge building in over the
mainland from the Bering while the EC keeps the ridge flatter
with a bit more unsettled weather over the area. Ensembles do show
high pressure trying to build in from the North Pacific though
the flow becomes more zonal in nature as an upper level low tries
to push down from the Arctic. For now, trended towards the more
unsettled solution until models show better agreement on the
building ridge next weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch...125.
MARINE...Gales...130 131 132 137 138 139 150 160 165 173 176
 180 352 414.
 Storms...170 172 174.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...AH/RMC
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...KVP


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