Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
504 am akst sun Nov 29 2015
Analysis and upper levels...
the current upper level pattern remains very similar to that of
the last few days. The most significant features are a broad long
wave trough centered over the Bering...with a sharp blocking ridge
stretching from the southern Panhandle down to the West Coast of
the lower 48. A weak shortwave trough is bringing mainly rain
showers to the southcentral and the Gulf Coast...while a weakening
pressure gradient continues to bring gusty gap winds to the Gulf
Coast. This gradient is also bringing weak downsloping to the Lee
side of the chugach range...which is keeping most of the rain
showers around southcentral from reaching the ground from the
Anchorage bowl eastward into the Copper River basin. Over the
central Aleutians...a gale force low and associated front is
centered under the longwave trough...and is beginning to spread
rain and gusty southerly winds into the akpen. Over the southwest
Mainland a weak area of high pressure is bringing patchy
fog/stratus to the area...especially for the interior Kuskokwim
Delta and Bristol Bay.
the models continue to be in excellent synoptic agreement with the
track/intensity of the Aleutian low into middle week. As the result
the higher resolution models were used again tonight to better
capture gap winds and precipitation from the front moving into the
Gulf on Monday. There remains very good agreement that cross
barrier flow along chugach and Kenai Mountains will keep most of
the rainfall confined to the Gulf Coast into Tuesday.
Short term forecast southcentral Alaska (days 1 and 2)...
the upper level trough over the northern Gulf and south central
Mainland will continue to move north through this evening and
weaken as it does so. Precipitation will be mainly confined to
coastal and up-slope areas...with very little precipitation
inland. This system will dissipate tonight as a ridge builds over
south central Alaska ahead of the next front approaching from the
southwest. The leading front from this next low will reach Kodiak
Island tonight and the Gulf Coast on Monday. This front will then
become much more east-west oriented as the responsible upper low
stalls out just south of the Alaska Peninsula later Monday and
Monday night. This will again keep most of the precipitation
confined to the coast. Temperatures will gradually cool over the
next couple of days...but remain well above normal with continued
southerly flow aloft.
Short term forecast southwest Alaska (days 1 and 2)...
the southwest is under onshore flow...with light winds combined
with moisture in the region producing areas of fog with some
places having dense fog at times this morning. An upper level
trough will move through today producing showery precipitation in
the southwest area. By late Sunday night as the North Pacific low
tracks along the eastern chain...the associated weather front will
move into the Bristol Bay region. This will bring another round of
precipitation to Bristol Bay before spreading inland accompanied
by gusty southeasterly winds heading into Monday.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
the central Aleutians will have a gale force low located west of
Dutch Harbor this morning before this system tracks to the eastern
Aleutians by Monday morning. This will bring gale force winds to
the eastern Bering Sea by late Sunday night. By Monday the Bering
will predominantly have gusty northerly winds with a showery
Long term forecast (days 3 through 7)...
Beginning the extended period on Tuesday morning...a broad upper
low centered over the eastern Bering and North Pacific will
encompass the entire region as the North Pacific jet remains
centered in the vicinity of 40n. A secondary low in the vicinity
of the Alaska Panhandle will rotate west into the northern
Gulf...spreading rain and snow along the Gulf of Alaska coast.
Inland locations will remain under the influence of moderate east
to southeast flow...with this downslope shadow keeping
precipitation mainly confined to coastal and marine locations.
Farther west...the bulk of cold Arctic air will remain over the
western and central Bering Sea...with extensive instability
showers and strong northwest winds. With an Arctic high centered
north of the North Slope of Alaska...colder surface level air will
infiltrate southern Alaska...allowing temperatures to moderate and
cool back to near normal heading into the late week. Another North
Pacific low will merge with the Arctic trough late
week...deepening into a deep low somewhere across the southern and
eastern Gulf of Alaska. Much uncertainty arises by this
point...but some guidance drives in a strong storm force low
through the Gulf of Alaska late Friday into Saturday...but there
remains too much uncertainty with track and position to really get
excited at this juncture. Either way...the general pattern of cold
air over the Bering and strong easterly low to middle level flow over
southern Alaska will keep precipitation largely relegated to
coastal locales...with no dramatic change in the sensible weather
inland. Heading through the weekend...the North Pacific jet stream
will move east...with storminess continuing to impact the
Panhandle of Alaska as southern Alaska remains under the influence
of weaker lows dying in the Gulf of Alaska. In other words...no
significant inland storms are expected through the extended
period...with near normal temperatures.
marine...Gale Warning 130 131 132 150 155 160 170 172 173 174
175 176 180
Synopsis and model discussion...dek
southwest Alaska/Bering Sea/Aleutians...pld