Area Forecast Discussion
Issued by NWS Anchorage, AK

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
FXAK68 PAFC 290112

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 PM AKDT Wed Jun 28 2017


Water vapor satellite imagery shows two closed low pressure
systems impacting southern Alaska and surrounding waters this
afternoon. The newest closed low formed quickly overnight as
shortwave energy rounded the base the broad trough that expands
across the Bering to the central Gulf of Alaska. This low center
was located approximately 200 miles south of Kodiak Island early
this afternoon and is advecting abundant subtropical moisture
over the gulf and across Bristol Bay. Rain developing along the
surface low associated with this system, is along a band stretching
across the central gulf to Kodiak Island to the Aleutian Range.
Gusty small craft winds have increased along the this boundary
from the south and east directions. Visibilities reductions along
the frontal band are less than one mile as indicated by automated
stations from Kodiak Island.

To the west, the second upper low is a mature system spinning 250
miles north of Saint Paul Island. This stacked system is losing
momentum on it northward track as it dissociates from the
subtropical jet which lies near 45N. Low clouds and patchy fog
encompass the Bering along with a few showers as weak shortwaves
circulate around the core.


Models are in general agreement through Friday however they are
lacking in agreement between on refined details of precipitation
timing and coverage. The main edits for in the short term were
focused on rain chances during the next two days as this is the
main challenge for the end of the week.



VFR conditions are expected to prevail through the next TAF
package. Gusty south flow tapers off late this evening, remaining
light through Thursday afternoon. Rain spreads into Anchorage from
the gulf later this evening and continues through Thursday as a
weak boundary stalls across the region.



Satellite imagery this afternoon depicts another impressive surge
of Pacific moisture moving north toward the Gulf Coast in
association with a left-exit region of the subtropical jet
stream. Rain will work inland starting from the Kenai Peninsula
then into Anchorage and the Susitna Valley by tomorrow. The
Matanuska Valley may see a bit more downslope flow, so for now,
the best chances of rain will be from Anchorage South and then
northward toward the Alaska Range. Strong gap winds down Turnagain
Arm will weaken tonight as the pressure gradient bends the wind
down-inlet. The front will weaken along the coast Thursday night
and Friday with precipitation tending to favor the coast. Inland
drying will result in slightly warming temperatures Friday and
SAturday, and possibly some breaks of sun.



We remain in this pattern of the upper low over the central Bering
Sea rotating pulses of energy around it along the Aleutians to the
Bering Sea coast. One such pulse is now pushing through the
Kuskokwim Delta today producing widespread rain. This trough moves
north out of the Kuskokwim Delta region by this evening. The
overall flow weakens this evening and we should see a break in the
rain. In Bristol Bay, moisture from a low moving north into the
western Gulf of Alaska will spread across the Aleutian Mountains
and Alaska Range tonight increasing the chance for rain. The cross
barrier flow is not very strong, but we will likely see less rain
on the lee side of the mountains while the Kilbuck and Ahklun
Mountains will see heavier rain Thursday. Thursday night and
Friday the Gulf low will weaken and move across the eastern Alaska
Peninsula into Bristol Bay. Therefore we expect a continuation of
the wet cool weather over the Bristol Bay zone Friday.



The persistent Bering Sea low will remain the dominant feature for
the weather through Friday. It will move to the northwest as it
weakens, thus wind along the Aleutian Islands will diminish. A
low forming south of the western Aleutians becomes entrained in
the flow of the Bering Sea low and will rapidly move along the
Aleutians to the Alaska Peninsula as an open trough by Friday. The
main impact of this system will be increase rain potential.
Following this weak system we have yet another storm moving into
the western Bering Sea Friday. The front will move through the
western Aleutians Friday bringing minimum gale force wind as it


.LONG TERM FORECAST (Days 3 through 7)...
Long term models have not come into any closer agreement than they
were yesterday on the timing or placement of low pressure systems
in the Bering Sea and Gulf of Alaska. The same general pattern
continues with a strong jet streak diving into the western Gulf of
Alaska Sunday night, however the models diverge greatly on surface low
development and movement. GFS favors a further north solution
while EC pushes the low further south along the Gulf of Alaska
border. Both models continue to favor a wet Sunday and Monday for
most of the mainland but GFS does harbor some hope that things
might dry out a little bit for the Tuesday holiday. Meanwhile in
the Aleutians, model variability is high, with EC indicating a
rainy low pressure system moving through, and GFS indicating broad
westerly flow with significantly less precip. By Tuesday
afternoon, both models move a ridge into the eastern Bering, which
would dry things out in Western Alaska for the evening of the 4th
of July. Current thinking is to not adjust the long term
forecast, which would continue to bring rain through the early
part of next week.


MARINE...Gale 119 120 131.



LONG TERM...LF is the U.S. government's official web portal to all federal, state and local government web resources and services.