FXAK68 PAFC 071245
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKDT Fri May 7 2021
.ANALYSIS AND UPPER LEVELS...
In the upper atmosphere there is a pronounced area of troughing
from Kodiak to SE Alaska, a ridge axis well south of the AK PEN
in the North Pacific and and another deep trough over the Western
and Central Bering that extends south of the chain. On satellite
imagery there is a mature frontal boundary with an occlusion in
the Bering and a widespread cloud shield over much of Southcentral
associated with the remnants of a different low. The radars at
Kenai (PAHG) and Middleton Island (PAIH) have detected light
showers but nothing organized.
Currently, there is a Flood Advisory for an ice jam in Aniak along
the Kuskokwim River. Additionally, a Flood Watch remains in effect
for a different section of the Kuskokwim River which includes the
villages of Upper Kalskag, Lower Kalskag, Tuluksak, Akiak,
Kwethluk and Akiachak.
Models are doing decent with the placement of the major features.
However, when it comes to pinging into the showers detected by
PAHG and PAIH the NAM, the GFS and the ECMWF were barren in the
vicinity of PAIH and only the Canadian picked up on these showers
by Middleton Island. But the NAM and the GFS as well as the
Canadian did pretty well depicting showers by Denali and over
Southcentral. The models also were in sync with the precipitation
shield in the Bering and Aleutians.
PANC...At the onset of the TAF period, expect VFR conditions and
light winds. Light rain showers have been detected by the radar
at Kenai near PANC and will continue to be monitored. Around 23z
the winds will increase at PANC.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A cold-core upper level low is just north of Seward early this
morning and moving northward. The surface front extends from the
northern Kenai Peninsula to the southeast. This is putting the
main area of lift over Prince William Sounds with some showers
making it across the Chugach and Talkeetna Mountains. This wave
will move over the Alaska Range and into the Interior late this
The front can be easily seen on satellite as there is a sharp
break in the clouds behind this front. This clearing will be
relatively short lived as a second system, very similar to the
first, moves into the area. This second system will bring rain
into Kodiak by late this morning and weaken as it moves into
Southcentral. This is a slow moving system with the cold-core
upper level low expected to track to near Seward Sunday afternoon.
By then, Kodiak will be back in the rain due to a third front
taking a similar track over the area.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A quiet start to the forecast period is expected as upper level
high pressure extends across Southwest Alaska today. This upper
level high pressure will result in partly cloudy skies and light
winds. A front will approach Southwest Alaska late Friday night
and bring showers to Bristol Bay and the southern Kuskokwim Delta.
Shower activity will increase north and east throughout Saturday
as the front gradually lifts northward. The greatest chance of
showers will be around the coast and the lowest chance will be the
farthest inland locations in the Kuskokwim Valley. The unsettled
but benign weather will continue into Sunday as shower activity
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
An unsettled but benign weather pattern is expected to continue
across the Bering/Aleutians over the next 3 days. A broad low
continues to weaken while remaining nearly stationary over the
central Bering/Aleutians. Winds will generally remain below Gale
force, with the exception of coastal marine zone 150 as pressure
gradients will be sharp enough in that location to produce Gale
force winds today. These Gale force winds in marine zone 150 will
weaken this evening. For the remainder of the period winds will
remain below Gale force with no high seas expected.
.MARINE (Days 3 through 5: Sunday through Tuesday)...
A broad area of low pressure will maintain winds less than 35 kts
and seas less than 20 ft over the Bering and the Gulf of Alaska.
Long Term Forecast (Days 3 through 7: Sun through Thu)...
Looking ahead into the extended forecast, model guidance are in
overall agreement with the latest synoptic features affecting the
entire forecast areas for late this weekend into Monday, but
diverge significantly in the early to the middle part of next
week. Starting with the Gulf, continued widespread rain over
Kodiak Island associated with a North Pacific low and front will
spread further northward across the Eastern Kenai Peninsula and
coastal areas of Prince William Sound. A few isolated showers are
possible further inland as well as near surrounding terrain, with
mostly dry conditions over Anchorage Bowl and the Mat-Su Valleys.
Thereafter, models seem struggle with the track of the next upper
level shortwave and associated surface low advertised late Monday
night and the extent of the precipitation, timing, and duration
in the aforementioned areas.
Further west, there is moderate confidence that an elongated
trough encompassing the entire Bering Sea will eject multiple
shortwaves with associated surface lows, thereby maintaining a wet
and showery pattern along the Aleutians and the Pribilofs through
Tuesday. The bulk of the rain showers seem to be concentrated
over the Eastern Aleutians with enhance rainfall along the AKPEN
attributed with a deep fetch of moisture and orographic lift.
Where models begin to diverge and therefore increase uncertainty
is determining whether or not an upper level shortwave from the
Kamchatka Peninsula will merge with aforementioned Bering trough
or be the main weather producer driving systems over the Bering
and along the Aleutian Chain. Future model runs will be needed to
resolve specific details including precipitation timing and the
potential of gusty winds blowing through the terrain gaps and
passes. Suffice to say that unsettled weather will be the theme
with a few showers possible over the Coastal Southwest.
PUBLIC...Flood Watch and Flood Advisory 155.
MARINE...Gale 138 and 150.
SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED