Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
500 am akst Thursday Dec 5 2013
Analysis and upper levels...the ridge over the Mainland remains
persistent this morning...while a longwave trough continues over the
Bering Sea. Relatively weak surface lows are continuing to move
northward through the eastern Aleutians into the central Bering Sea
with this pattern...bringing abundant warm air northward into the
eastern Bering and southwest Mainland. While most locations across
southwest Alaska have warmed up above freezing...temperatures east and
south of the Alaska Range continue to be below freezing this morning.
Freezing rain has been falling intermittently over several locations
in the Cook Inlet region overnight.
models start out in good synoptic agreement...with the latest runs of
each model appearing to have a better handle on the moisture and
dynamics that exist. Overall the vorticity and areas of quantitative precipitation forecast look very
similar from model to model. The NAM is the preferred model for the
short term in the east area...while the European model (ecmwf) is the overall model of
choice for the southwest Mainland and Bering Sea areas. Greater model
differences begin to show up by Saturday...as a pattern change
begins. At this point we are blending the European model (ecmwf) and GFS solutions
until details become more clear.
Short term forecast...
southcentral...early morning radar images indicate that freezing rain
is developing again as expected from the northern Kenai Peninsula to
southern Susitna Valley. This is occurring as a shortwave stretching
from Kodiak Island into the western interior approaches Cook Inlet.
Because of this...the freezing rain moving through northern Cook
Inlet this morning will be more widespread and continuous that the
intermittent areas of mixed precipitation that moved through
yesterday evening. This freezing rain will continue to develop over
the course of this morning...and reach its peak intensity in the late
morning/early afternoon before becoming just rain early this evening.
Periods of rain will begin to diminish late this evening...which will
bring in a potential for areas of fog to develop overnight tonight
due to the preconditioned moist boundary layer. After a slight chance
of mixed precipitation for Friday throughout southcentral...the area
will then begin to clear out again this weekend as the ridge over the
Gulf begins to rebuild.
Southwest Alaska/Bering Sea/Aleutian chain...after the current low
near the pribilofs moves off to the north...high pressure will build
into most of the Bering Sea from the southwest. A low will spin south
of the eastern Aleutians and Alaska Peninsula...affecting the area
with gale force winds and rain into the weekend. Temperatures over
the Mainland will remain fairly mild through the weekend...such that
any precipitation that falls will generally be liquid.
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 would be a good
bet for much of the southeast Mainland from Sunday into the middle of
public...Freezing Rain Advisory 101 111 121 125 145 152
gale 131 138 150 155 170 172 173 176 178 179 180 411 414
Kochevar/schreck Dec 13