Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
156 PM akdt Friday Aug 22 2014
Analysis and upper levels...
the main feature is the closed upper level low anchored over the
western Aleutians and a broad Flat Ridge of high pressure
extending into the Gulf of Alaska. The jet stream wraps around the
low extending across the top of the Gulf Ridge then heads
southeast along the Pacific coast into the Pacific northwest. A
weak disturbance is south of the Alaska Peninsula heading north in
the overall flow pattern. Two other weak disturbances are on tap
in this flow pattern well south of the Aleutians and will move
toward the Alaska Peninsula then into the eastern Bering Sea over
the next couple of days.
The models are in generally good agreement into the beginning of
next week. The models diverge on the solution of the storm
expected to move into the western Aleutians in the middle of next
week with the GFS having a faster movement of the low to south of
the western Aleutians than the European model (ecmwf). By Thursday the models come
into better agreement on the solution of this low deepening it to
the middle to upper 990 mb range with the front moving across the
central Aleutians Thursday.
Short term forecast...
unstable conditions will result in isolated showers and
thunderstorms over the southern Susitna Valley west of Big Lake
this afternoon and evening along with some isolated shower
activity along the Chugach Mountains. High pressure over the Gulf
of Alaska will hold the coastal areas in the stable air for
another night before the next low moves to the Alaska Peninsula
Saturday. Expect the radiational fog over Prince William Sound the
north Gulf Coast and Cook Inlet to occur again tonight and
As the low moves over the Alaska Peninsula late Saturday expect
an increase of moisture to flow into the south Central Area in the
southwest flow resulting in cloudier cooler conditions for Sunday
the upper level and surface low will move from the central
Aleutians to the eastern Bering Sea and Bristol Bay area through
Saturday bringing cloudy cool conditions to the region through
the weekend. The best chance for rain will be along the Alaska
Peninsula and coastal locations along Bristol Bay and the
Kuskokwim Delta Saturday. By Sunday the surface and upper low will
be over southwest Alaska resulting in clouds and rain likely over
the entire region. As the low approaches the Alaska Peninsula
tonight expect the wind to increase through the passes of the
Rain will persist over the eastern Aleutians and spread across
the Pribilof Islands this evening. Showers will linger across the
central and eastern Bering through Sunday as the low moves east.
Weak high pressure over the western Bering will persist into
Saturday before another low spreads rain into the area Sunday and
Long term forecast...
an upper level low will be positioned over the northern Gulf of
Alaska Tuesday morning as it tracks into the Yukon territory by
Wednesday. Resulting in showery conditions for the southeast
Mainland. Followed by an upper level weak ridge briefly bringing
drier conditions for Thursday. By Friday an upper level trough
drops down from the north bringing more clouds and showers to the
region going into the weekend. The Bering Sea will have an upper
level long wave trough near the Kamchatka peninsula dropping down
into the western Bering Sea and western Aleutians by Tuesday.
The models are struggling with this is feature with the position
of the surface low at the base of the trough near the western
Aleutians. This system will slowly move eastward across the
Aleutians from Wednesday into next weekend. This will produce
showery conditions with marine layer stratus and fog.