Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
141 PM akdt Wednesday Jul 23 2014
Analysis and upper levels...
there is an upper level low over the northern Gulf of Alaska.
There is a north/south oriented trough just west of central
Alaska...associated with a low in the Arctic Ocean. There is a
large and strong ridge over the southwest Bering Sea.
the numerical models are in fairly good agreement through 84
hours. There are still some differences in how they handle
energy/moisture as it splits into the the northern trough and Gulf
low. Confidence in the forecast for the afternoon package is a bit
higher than normal.
Short term forecast...
the large scale pattern will remain basically unchanged through 84
hours. The ridge over the southwest Bering Sea will slowly drift
eastward into the central Bering by Thursday afternoon and
remaining there through Saturday. The Mainland trough/Gulf low
will remain in nearly the same areas...with a bit of a drift
eastward as well.
For south central Alaska...the Gulf low will slowly drift east
tonight and Thursday morning. This will leave south central in a
"col". This will result in just some minor shower activity with
some left over moisture and weak/nonexistent dynamics. The next
system will push more widespread rain into the Cook Inlet/Susitna
Valley area later Thursday. This will be a slow moving system as
it stretches apart with part of the energy moving north ahead of
the Mainland trough and part moving into the Gulf low. Although
the energy is weakened by the split...the slow moving nature of
the system will keep much of south central in positive dynamics
(and thus good chances of rain) well into Friday. Later Friday
through Saturday south central will again be in the "col" and
precipitation will taper off to just a few showers.
For southwest Alaska...northwest flow aloft and proximity to the
Mainland trough will keep considerable chances of precipitation
over the area through Thursday. On Friday the Bering ridge will
have moved far enough east to provide some protection to southwest
Alaska...and generally dry conditions are expected.
Long term forecast...
the long range pattern (saturday night through wednesday) will
generally consist of a strong blocking ridge over the central
and eastern Bering Sea...a longwave trough over the central and
northern Mainland...and a closed upper low over the southern and
eastern Gulf of Alaska. This pattern will result in northwesterly
flow aloft for much of the southern 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
The wpc (weather prediction center) forecast generally leans
toward the 00z European model (ecmwf) operational model run...which itself was in
line with the European model (ecmwf) and GFS ensemble means yielding fairly high
confidence in the synoptic pattern forecast through the middle of
Ludwig/Cassell Jul 14