Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
515 am akdt Friday Jul 25 2014
Analysis and upper levels...
Upper level trough over the eastern half of Mainland Alaska this
morning is split into two features. The main trough extends south
to the Alaska Range and is the current weathermaker with a wave
moving around it's base through southcentral. The second feature
is a cut-off low over the eastern Gulf. A ridge of high pressure
is also centered over the western Aleutians.
At the surface...a front extends across the Kenai Peninsula and
the mat-su...to the Talkeetna Mountains and the Alaska Range.
Abundant rain is falling with this front...with amounts accentuated
by it's extremely slow eastward movement. Elsewhere a broad area
of low pressure resides over the Gulf of Alaska with a high over the
Models agree on the general synoptic pattern with the development
of the deep trough over the eastern half of the Mainland and a
strong ridge of high pressure over the Bering. The forecast
problem is the timing and strength of waves moving around the
Bering high and diving into the southern portion of the trough
as it develops over the Gulf and northeast Pacific. Comparison of
jet stream solutions shows the ec to have strong nearly meridional
flow that drives energy from the northern trough into the base of
the Gulf trough. This would accentuate the amplitude and result in
an increasingly unstable configuration. The forecast utilizes the
GFS solution...which is not as aggressive in increasing the
amplitude of the trough and which will allow the configuration to
maintain itself for a longer period.
This means that today's wave/front will move across southcentral
into the copper rive basin by tonight. It will also reach the
akpen today and tonight. On Sat a wave over Southeast Alaska moving
around the Gulf low will enhance precipitation over the Copper
River basin Sat into sun.
The second wave moving around the Bering low will reach western
Alaska tonight and southcentral on sun. The third wave reaches
western Alaska sun and dives across the akpen Sun night into Monday.
Short term forecast...
Rain will begin to taper off this afternoon and evening from the
west as it simultaneously intensifies over the Copper River basin
tonight into Sat and where it persists into Monday. Another round of
rain crosses the Alaska and Aleutian ranges later on sun into Monday.
Dry and increasingly sunny conditions will persist until rain
returns sun into Monday.
Low clouds...fog...and some drizzle can be expected through the
Long term forecast...
A highly amplified pattern will exist across the region on
Monday...with a high amplitude ridge over the Bering Sea...and a
large upper low in the Gulf of Alaska. A shortwave trough will
drop into southern Alaska late Monday into Tuesday...supporting
showers across most of southern Alaska. Eventually...the large low
in the Gulf will lift north into southern Alaska...with increasing
threats for easterly waves to rotate into the Mainland...keeping
the threat for showers and periods of rain through the end of the
week. Temperatures will generally hover around normal across the
Mainland...with daily temperature trends heavily modulated by the
timing of individual easterly waves. Across the Bering...the high
amplitude ridge will generally support widespread fog and
stratus...with rain threats largely remaining over the western
Ds/ja Jul 14