Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
143 PM akdt Tuesday Jul 22 2014
Analysis and upper levels...
there is an upper level low centered over Bristol Bay...and an
upper level trough that extends north/northeast from the low with
its axis running through Bethel to near Barrow. There is a large
and strong ridge centered over the southwest Bering Sea that is
nudging into the central Bering. There is a ridge over Southeast
Alaska that is being eroded by the western Alaska low/trough.
the numerical models are in good agreement through about 60
hours. From 60 to 84 hours the models begin to disagree somewhat
on the strength/speed/orientation of short-waves swinging south on
the backside of the trough/low which by this time will be over
central Alaska/northern Gulf. The models do continue to agree well
on the ridge over the Bering Sea. Forecast confidence for the
afternoon package is near to above normal.
Short term forecast...
For south central Alaska...the ridge that has been over the area
will slide off to the east tonight as the Bristol Bay low pushes
across Kodiak Island...then into the northern Gulf of Alaska on
Wednesday. The low will then stall over the northeast Gulf on
Thursday and remain there through Friday. On Wednesday night and
Thursday a system pushing out of northeast Russia will re-enforce
the trough over western/central Alaska. This system will push into
south central Thursday night...then it will split apart to the
north and south of the Gulf low on Friday. The trough (by this
time situated north/south over the center of the state) will
"sharpen up" on Thursday and Friday as the southwest Bering Sea
ridge moves into the central Bering Sea.
For southwest Alaska...the trough/low will push through tonight
bringing rain/showers to most of the area. The "re-enforcing"
system will push into southwest Alaska from the northwest late
Wednesday into Thursday. On Thursday night and Friday the flow
aloft will be fairly strong from the north-northwest as the ridge
builds into the central Bering Sea. Thursday night and Friday look
fairly dry as the Bering ridge will nudge most of the moisture to
For the Bering Sea/Aleutians...the main story will be the ridge
over the southwest Bering Sea building eastward. Light and showery
precipitation will be nudged eastward ahead of the ridge. The
strong stability associated with the ridge will cap the marine
layer and keep plenty of low clouds and fog across the
area...which of course is the type of weather that is expected
this time of year.
Long term forecast...
the long range pattern (friday night through tuesday) will
generally consist of a strong blocking ridge over the central
Bering Sea/Aleutians and a trough over the Gulf of Alaska and over
northern Alaska. This will result in northwesterly flow aloft for
the Mainland. A few systems will push through southern
Alaska...bringing considerable clouds and some precipitation. Due
to the direction of the upper flow and the fact that these systems will
be transient...precipitation will generally be showery and
accumulations are not expected to be very high.
The wpc (weather prediction center) forecast generally leans
toward the 00z European model (ecmwf) ensemble mean...but even the operational
European model (ecmwf) and GFS as well as the GFS ensemble mean are not all that
Ludwig/Cassell Jul 14