Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
200 PM akdt Tuesday Oct 21 2014
Analysis and upper levels...
500 mb...the upper levels continue to be dominated by a large low
over Bristol Bay and a high amplitude ridge over the Bering Sea.
The Bristol Bay center is expected to drift south and weaken as a
low center over the eastern Gulf moves west and anchors over the
southern Gulf Wednesday. This low then drifts southeast on Thursday as the
ridge over the Bering Sea moves over western Alaska. A wave moving
across eastern Russia sets up westerly flow across the Bering Sea
Surface...a weak deformation zone was evidenced by clouds and
showers across the northern Gulf and Kenai Peninsula this afternoon. A
large 970s mb low was present over the south Gulf of Alaska with
weak high pressure over the main land. A few snow showers
associated with a low near Bristol Bay and broad upper trough were
evident over SW Alaska. Brisk northerly winds and cold advection
were continued across much of the central and eastern Bering Sea.
Satellite imagery showed a large area of open/closed cell cumulus with
showers across the Bering Sea/Aleutians.
Models are in excellent agreement with the general large scale
pattern through the latter part of this week. Main differences
come in to play with the handling of frontal boundary moving
across the Bering Sea and impacting the SW Mainland Thursday. The GFS
is a little slow on the frontal movement and pushes a little too
much warm air into the western Mainland Thursday night.
Short term forecast...
a broad band of moisture associated with a weak deformation zone
heads south and brings some rain/snow to the western Gulf/Kodiak
Island tonight. Dry offshore flow and building pressure gradients
develop behind this system tonight. In response brisk gap winds
are expected around southcentral...especially the Gulf Coast and
eastern Kenai Peninsula. A few showers are possible across the north
Gulf and Copper River Wednesday night with a weak wave...otherwise the
next shot at snow will be on Friday.
steady snow across the Delta this morning has moved
offshore...with a general drying trend through Wednesday as a
northerly flow pattern develops. A front will approach from the
west Thursday afternoon into Friday...spreading snow inland with a
mix along the coasts. Rain and snow showers will intensify some
across the Alaska Peninsula was the upper trough drifts south. Increasing
northerly winds are also expected with strong lows through gaps in
the peninsula on Wednesday.
strong northerly winds and rain and snow showers will continue
across the eastern and central Bering and Aleutians through
Wednesday. A front will track into the western Bering Wednesday
then spread through the Bering while weakening Thursday and
Long term forecast...
Run to run guidance of the extended models has not been
good...at least partially due to handling of the moisture residue
from Tropical Storm Ana. Earlier ec models were bringing the
residue along with a deepening low into the Gulf of Alaska on Monday...but
more recent runs are sending the moisture field east...with a much
weaker low over the eastern Gulf Monday through Wednesday.
While this is happening...a front associated with a low over
northwest Alaska will move across Mainland Alaska through the
weekend...followed by high pressure early next week. A Kamchatka
low will send a frontal complex across the Bering to western Alaska
sun through Wednesday.
The forecast utilizes the wpc solution...which relied heavily on
the 06z GFS ensemble forecast that provided some run to run
Marine...gales 150 155 170 171 172 173 174 178 179 185 351 352.
Rmc/ds Oct 14