Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
400 PM akst Thursday Dec 5 2013
Analysis and upper levels...the persistent ridge over the Mainland
has pushed slightly to the east. The longwave trough over the Bering
Sea will become less amplified and lifted northward overnight.
Relatively weak surface lows continue to move northward through the
eastern Aleutians into the eastern Bering Sea as they break off from
the main low in the North Pacific...which has become nearly
stationary as it interacts with the ridge in the Gulf. Warm air will
continue to advect northward from the North Pacific along the western
portion of the ridge and into the eastern Bering and southwest
Mainland. High pressure begins to build over the western Aleutians
Friday morning and will remain the dominant feature over that area
through the weekend.
the 12z model runs were in fair synoptic agreement with some
differences in the positioning and strength of both upper level and
surface features. However the most recent model run (18z) has
improved on these features between the GFS and NAM. The NAM is the
preferred model for the short term in the east area...while the
GFS/European model (ecmwf) is the overall model of choice for the southwest Mainland
and Bering Sea areas. Slight model differences begin to resurface by
Friday evening...as the overall synoptic pattern begins to change.
Short term forecast...challenges abound in the short term period in
the Cook Inlet through Susitna Valley region. A Stout band of
freezing rain that passed through the Anchorage and Matanuska Valley
earlier today is weakening as it continue northward. Another upper
level disturbance is moving into the southern inlet early this
afternoon bringing some more precipitation to that area. The biggest
question at this time is whether this next wave will weaken as it
heads northward or if the precipitation will remain intact or
intensify. The atmosphere in the region is conducive for freezing
rain and will remain so into Friday. The exception is the southern
part of the Kenai Peninsula where temperatures have pushed above
freezing. After this wave moves through this evening there should be
a reprieve in precipitation as the upper level ridge builds back over
the area. However this will likely bring widespread fog and possibly
freezing drizzle to the Cook Inlet region this weekend.
Southwest...the Kuskokwim Delta will see some more periods of rain as
the next system moves northward. For most of the southwest Alaska and
Bering Sea region the precipitation type will be rain as warm air
from the Pacific continues to be pumped into the area. The exception
is the Kuskokwim valley where lower elevations could see a few more
shots of freezing rain as they remain below freezing at the surface
and above freezing for a portion of the higher elevations.
Long term forecast...once the Gulf Ridge rebuilds over the Mainland
this week...there is decent agreement that this will not redevelop
into another Omega block like was experienced last week. Major
synoptic scale features will likely remain west of southcentral into
early next week...however without significant middle level ridging
periods of precipitation and cloud cover for southcentral and Gulf
Coast cannot be ruled out. It appears that a mix of clear and cold
days...followed by cloudy...shower...and warmer days is a reasonable
bet for much of the southeast Mainland from Sunday into the middle of
public...Freezing Rain Advisory 101 111 145.
Marine...gale 131 150 155 170 172 173 175 176 178 179 180.