Scientific Forecaster Discussion
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
414 am akst Mon Dec 5 2016
Analysis and upper levels...
ridging has moved in over Mainland Alaska which has allowed for
continued clear skies and radiative cooling bringing cold
temperatures to locations all around southcentral and southwest
Alaska. Behind the ridging, a front is tracking through the
eastern Bering towards southwest Alaska. Further to the west,
another ridge is building in over the western Aleutians.
the models are in good agreement with the major synoptic features
heading into the mid term. The small differences that are there
with some smaller scale features will have little change in terms
panc...VFR conditions and light winds will persist.
Short term forecast southcentral Alaska (days 1 and 2)...
high pressure over south central Alaska this morning will slowly
be pushed north and east over the next couple of days as a low
over the eastern Bering Sea moves into the Gulf of Alaska. The
leading front with this system will move into Kodiak early today
and then to the Gulf Coast later today. Precipitation with this
system is expected along and near the coast. There is only a
chance of precipitation inland, with pops in the chance category
for the western Kenai and only a slight chance for Anchorage and
the Matanuska valleys late tonight into Tuesday. This is due to
the dry air and some lingering high pressure, as the low itself
stalls in the Gulf.
Short term forecast southwest Alaska (days 1 and 2)...
precipitation will return to portions of the southwest Mainland
today as a triple point low currently taking shape along the front
to the east of the Pribilof Islands tracks eastward into Bristol
Bay. This will produce a region of isentropic ascent on the
northern periphery of the low as warm advection aloft overruns the
very cold air which has been in place at the surface for the past
several days, with the bulk of the snow associated with this
system focused along the northern Bristol Bay coast beginning
late this morning and lasting into tonight. Up to 3 inches of
accumulation will be possible along a corridor from King Salmon
westward to Dillingham and the western CAPES by Tuesday morning.
Moving farther inland, 00z and 06z model guidance continues to
suggest that interior locations including Bethel and the lower
Kuskokwim valley will see much lighter precipitation and little
or no accumulation as the low remains farther to the south. The
low will then depart into the Gulf by Tuesday morning, bringing a
return of drier northerly flow which will yield clearing skies and
continued frigid temperatures heading into the middle of the week.
A few snow showers may also linger through Tuesday along the
Aleutian Range in cold advection on the back side of the low.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
the triple point low developing along the front will keep the most
active weather focused in the vicinity of the Alaska Peninsula
through Tuesday as the low moves eastward into Bristol Bay and
eventually the Gulf of Alaska. Precipitation will predominantly
fall as rain through this afternoon as the akpen remains in the
warm sector of the system, with a transition back to convective
snow showers tonight as cold advection commences in northwest
flow in the wake of the low. Elsewhere, the central Bering will
see benign conditions for the next several days as a narrow, high
amplitude ridge builds overhead. The next front will then move
over the western tip of the Aleutians by Tuesday morning, bringing
another round of strong southerly winds and potentially heavy
Long term forecast (days 3 through 7)...
a continuation of below normal temperatures and little
precipitation will characterize the extended forecast. Day 3
begins Tuesday afternoon with a weakening upper level low sliding
into the Gulf. There is little frontal activity with this system,
but a decent pool of cold air aloft (-35c to -40c) in which to
promote shower activity. The pattern will keep snow showers along
the north Gulf Coast through Wednesday, especially in the western
Prince William Sound area. The combination of high pressure in the
interior/Yukon and low in the Gulf will keep gap winds going from
Valdez through the Copper River Delta. Overall the pattern will be
very dry and cold through mid-week, however, some moisture could
make it over the mountains in the form of flurries.
The extended forecast looks to be much of the same as well,
continued Arctic air overhead with little threat for precipitation.
The two features that will shape the pattern are a developing
blocking high pressure over northwestern Alaska, and a large
anchoring siberian low pressure. The east Asian jet working around
the south side of the trough will be split as the blocking high
sends part of the energy south of the Aleutians. Confidence is
higher that we will remain in the dry and cold pattern through the
end of the week.
public...Wind Chill Advisory...145.
Marine...gale...127 130 139 178 411.
Heavy freezing spray...127 140 160 180 181.
Synopsis and model discussion...dk
southwest Alaska/Bering Sea/Aleutians...cumulonimbus