Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 261307
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 AM AKDT Thu Apr 26 2018

.ANALYSIS AND UPPER LEVELS...
An upper level low situated over the Bering Straight is leading to
a broad area of cyclonic flow across most of the state this
morning bringing continued cool and unsettled weather over most
of the region. Persistent moist southwesterly flow combined with
a pool of cold air aloft is leading to widespread showers over the
southern half of the mainland, with periods of heavy rain seen
over the Gulf coast, Bristol Bay coast, and over the Kuskokwim
Delta this morning. The strong southerly flow is organizing these
areas of showers into narrow bands, leading to high variability in
the precipitation coverage this morning. A shortwave ridge is
beginning to build in across the western half of the Bering Sea
and Aleutian Island chain bringing a brief lull in the weather,
though widespread stratus is developing underneath the ridge axis.

&&

.MODEL DISCUSSION...
The models remain in good overall agreement through the rest of
the week with the timing of a series of short waves that will
rotate around the upper low this week. There continue to be model
differences in the placement of individual precipitation bands
today, thus used scattered or widespread coverage to capture the
spatial uncertainty of precipitation. Looking into Friday, models
are in good agreement with a surface low dropping south from
NE Russia into the AK mainland, increasing confidence of
widespread snow over southwest and rain/snow over southcentral.

&&

.AVIATION...
PANC...The terminal will remain predominately VFR through the day
as showers moving north up the Cook Inlet this morning should
stay to the west and east of the Anchorage Bowl. Gusty SE winds
should slacken a touch this morning before the Turnagain Arm
winds kick up again later in the afternoon. As the surface warms
and instability increases this afternoon, showers will become more
widely scattered with convective bands forming over the Chugach
and possibly downstream of the terminal. As a shortwave trough
moves through this evening, mid-level winds will become more
southwesterly directing any showers forming over the Kenai towards
the terminal.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

The large upper long wave trough still anchored over the eastern
Bering Sea/western Alaska will send a fairly well defined short
wave over the Cook Inlet to MAT-SU corridor this afternoon. This
wave passes through tonight, however, another more prominent wave
replaces it Friday afternoon. Unstable conditions will prevail as
cold air moves over the region supports shower development. The
main focus of showers will be with the short wave which moves in
today and the next wave which moves in on Friday. Cold air moving
in aloft combined with mild daytime temperatures will make for a
challenging precipitation type forecast. Overall, lower
elevations will see rain showers with a transition toward snow
showers in the mountains and northern Susitna Valley. A mix of
rain and snow showers are still possible at lower elevations
especially during the overnight hours and in the vicinity of
heavier showers. Stability indices today over the western Kenai
Peninsula could support isolated thunderstorms or certainly
locally heavy shower activity.

Gusty gap flows are still expected across Turnagain arm, out of
Knik Valley, and along the Copper River today through Friday.
Additionally, brisk southerly winds will develop over the western
Gulf/Cook Inlet tonight with the approach of the trough from the
west. Winds will likely hold until after trough passage later
Friday.

 &&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A low near the Bering Strait is bringing broad southwesterly flow
to southwest Alaska resulting in showers over the area that will
linger through the day. Tonight a shortwave will push across the
northern Bering and move through southwest Alaska bringing a
short, but heavier, round of snow. Weak ridging will then move
over the area before a front from the Bering makes its way to the
southwest coast by Friday evening. The front will pull up a lot of
warm air from the south which will transition much of the snow to
rain as it pushes inland Friday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging over the western Bering will keep the Aleutians in
westerly flow with minimum precip today until a front from the
North Pacific tracks over the western Aleutians this afternoon.
The front is pulling up a significant amount of warm air and will
primarily bring rain as it tracks across the Aleutians through
Friday. By Friday evening it will have made it to the southern
mainland leaving the Bering and Aleutians in broad westerly flow.

&&

.LONG TERM FORECAST (Days 3 through 7)...
A system over Southeast Alaska Friday evening will quickly move
east and dissipate Friday night. A fairly significant upper low
will be over the central/eastern Bering Friday night. The leading
front will push across southwest Alaska early Saturday morning
and then into the Gulf and Southcentral during the day on Saturday.
The upper low will move eastward across the Gulf Saturday night.
A fairly strong surface low will move into the Bering on Saturday.
After this, the model guidance begins to diverge. The models
agree on continued fast zonal flow aloft, along with the general
idea of an upper low in the Bering and upper ridging over the
northeast Pacific into eastern Alaska. However, the location and
timing of various systems has a large spread in the guidance.
Therefore the fairly active weather pattern will continue, with
the details not well defined. Thus the WPC guidance begins to lean
fairly heavily on the ensemble means after Monday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...155 165 170 172 173 174 175 176 177 178 179.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KVP
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...BL



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