Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
150 PM akdt Friday Aug 29 2014
Analysis and upper levels...
The large scale synoptic pattern is characterized by three upper
level lows across the region...with a zonal North Pacific jet
stream stretching from the Bering to the southeastern Panhandle. A
cold upper level vortex is situated over the North Slope of
Alaska...with a positive tilt trough...currently
deamplifying...over the Bering Sea. Water vapor satellite imagery
depicts a low amplitude shortwave trough diving into the Gulf of
Alaska in northwesterly flow...with another shortwave trough in northwest
flow tracking into the y-k Delta. A deformation zone is situated
over the Copper Basin...promoting extensive cloud cover and light
precipitation. This general pattern is driving an offshore surface
flow across the northwest Gulf of Alaska...and a general north-
northwesterly surface flow over southwest Alaska. With
time...drying and clearing will commence as drier and more stable
air moves into the Mainland through the Holiday weekend.
The numerical models are in excellent agreement with both the
large scale pattern and the smaller scale pattern into early next
week...and they remain in good agreement with the general large
scale pattern through late next week. Due to this...the NAM and
European model (ecmwf) were preferred for this forecast.
Short term forecast...
the upper low is making slow progress eastward this
afternoon...with steady rain continuing across much of the Copper
Basin and Prince William Sound area. Farther west across Cook
Inlet into the Susitna Valley...extensive low and middle level clouds
remain...and will likely remain in place through the evening. Some
clearing overnight will allow for strong radiational cooling and
the development of localized fog overnight into the morning.
Drying and clearing will commence for the weekend...with low
temperatures bottoming out across parts of southcentral Saturday
night...with the possibility of localized frost across low lying
cold spots near Anchorage...the Matanuska Valley...and the Kenai
Peninsula. The only exception will be across the Copper Basin
where clouds and showers will linger through the weekend.
isolated showers will diminish tonight across
most of southwest as drier air builds into the region. The
exception will be across the far southwest portion of the Alaska
Peninsula where a weak low will track across tonight and early
tomorrow morning. A low will move into the Kuskokwim Delta from
the northwest late Sunday before spreading rain showers and clouds
into the remainder of southwest on Monday. Gusty northwest gap
winds will continue across portions of the interior Alaska and
Aleutian Range tonight and then again Saturday night through
A weak low in the central Bering will track into the eastern
Bering by Sunday...spreading rain showers across the Pribilof
Islands and eastern and central Aleutians. High pressure will
build into the western Bering...then build into the central and
eastern Bering Tuesday and Wednesday...with a return to low
stratus and fog.
Long term forecast (tue sept 2 - Friday sept 5)...
An upper level low centered over the Chukchi Sea will bring
southwest to westerly winds to the Bering Sea and southwest Alaska
through the middle of next week. This will generally bring more
cloudy and cooler conditions with scattered showers except
possible numerous showers along the Alaska/Aleutian Range. The
southcentral Mainland and the northern Gulf will have an increase
in clouds and precipitation as the flow shifts to more
southwesterly by midweek.
Ahsenmacher Aug 14