FXAK68 PAFC 170210
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
510 PM AKST Fri Nov 16 2018
.ANALYSIS AND UPPER LEVELS...
The main upper level low is over the western Aleutians with the
upper level ridge now over the Alcan border. A shortwave trough
is over Southcentral Alaska today and moving up Cook Inlet. This
wave is the focus of precipitation concerns around Southcentral
Models remain in good synoptic agreement through the weekend with
the details being the main difference makers. The biggest
questions pertain to the Anchorage to Mat-Su areas where the NAM
has significantly more downslope than the GFS. This is typical,
but it also means the difference between dry conditions and
freezing rain. The truth likely lies somewhere in the middle so
forecasts and additional products reflect that line of thinking.
PANC...The biggest weather question focuses on this afternoon
through evening and whether there will be any freezing rain that
makes it to the terminal. Radar shows good reflectivities over the
airport, but a significant layer of dry air from the surface to at
least a few thousand feet is evaporating the precipitation as it
falls. The question is whether the wave moving up from the south
producing the lifting will make it through the area before the
atmosphere saturates and rain can make it to the surface. Winds at
the surface will remain northerly keeping temperatures below
freezing, though they are above freezing from about 1000 ft up to
4000 ft so precipitation making its way to the surface will be
freezing rain. By the early evening, the threat of freezing rain
will have diminished. Even if there is precipitation, ceilings and
visibilities are expected to remain VFR.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A frontal system bringing rainy and windy conditions to the
coastal areas as it pushes into the northern Gulf will continue
to lift north this evening as its parent low tracks north towards
the southwestern end of Kodiak Island. The weaker portion of the
front lifting over the Anchorage Bowl and Mat-Su Valleys this
afternoon and evening is bringing significant warming aloft but
cold dry air at the surface is evaporating away much of the
precipitation falling through it. With northerly winds down the
Susitna Valley continuing to reinforce the entrenched low level
cold air mass there is potential for some areas of light freezing
rain especially over the southern Susitna Valley. As the front
over the north Gulf lifts north over the Copper River Basin
tonight through Saturday morning. Snow and freezing rain will
spread over that area as well with more substantial accumulations
from Glennallen southward.
Precipitation will taper off briefly midday Saturday before the
next frontal system swings into the southwestern Gulf Saturday
afternoon and continues north through the western Gulf Saturday
night to reach the northern Gulf Sunday. Additional frontal waves
will continue to track up from the south through Monday spreading
precipitation progressively further inland and keeping
temperatures on the warm side for this time of year.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Unsettled southerly flow will continue to bring a wintery mix to
Southwest Alaska as interior locations see a mix of rain and snow
with some isolated pockets of freezing rain over the Kusko Delta.
Along the coasts, precip type has largely shifted to all rain.
This will continue through tomorrow morning before a secondary low
moves in and reinforces the warm air aloft. This should allow for
a warm layer to develop over the Kuskokwim Valley, resulting in
areas of accumulating freezing rain (ice). This will occur by the
afternoon and will likely continue through the night into Sunday
morning (see winter weather advisory for more details). Expect
mostly rain for coastal areas with some mixing over the interior
portions of the Bristol Bay area and the Kusko Delta. Eventually a
slightly cooler air mass will move in from the west on Sunday and
into Monday, bringing in enough of an air mass change to
changeover to snow or a mix of rain/snow.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
A Bering front near the Pribilof Islands will continue to move
east and will strengthen as it merges with a North Pacific low
over Bristol Bay Saturday. This will help bring down decent cold
air advection and broad northerly flow over all of the Bering west
of Bristol Bay. Broad westerly flow will move into the Bering as a
series of occluded fronts move in Sunday and Monday with 15-30
.LONG TERM FORECAST (Days 3 through 7/Monday night through Friday)...
Disorganization and uncertainty continues for the long term.
Solutions are at least similar to yesterday in that we start next
week with troughing over southcentral AK and a closed upper level
low near SW Alaska. However, models are struggling with their
placement of the low over SW Alaska with variation in the
troughing extending from this low over the eastern and central
Aleutians. This means any frontal systems associated with this
low will be placed much differently at the surface. Therefore, we
still know weather will be active for much of the forecast area,
but the details are still very fuzzy.
Going forward through next week, a broad area of troughing
remains over southcentral AK, with disorganized lows spinning
through this trough. Once again, it is too far out in time to
predict particulars of these systems. Ridging exists over the
central Aleutians, while a trough is over the western Aleutians.
This trough/ridge pattern will be slowly working its way east
through the week, with models hinting at the ridge arriving over
southcentral AK on Friday.
PUBLIC...Winter Weather Advisory...141 145 152.
MARINE...Gales...119 120 130 131 139.
SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
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