Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 221451

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
551 AM AKST Sun Jan 22 2017

A very cold air mass remains entrenched across Southwest Alaska
under a deep upper level trough. Temperatures in a couple of the
coldest locations (Kalskag and Aniak) have fallen to minus 42
degrees with numerous other stations in the negative 20s and 30s
along the Kuskokwim Delta and lower Kuskokwim Valley. In
Southcentral Alaska the frontal band stretching from the Susitna
Valley across the Kenai Peninsula has weakened substantially with
the persistent snow in the process of gradually tapering off.

A rather potent frontal system has lifted north across the
Aleutians and into the southern Bering with scatterometer data
showing a widespread swath of storm force winds all along the
front. The associated surface low is currently south of Kiska
Island at around 950 mb and continuing to deepen rapidly. With the
cold air ahead of the front, very low visibilities due to the
combination of snow and strong winds are a significant concern
along the leading edge of the front as it pushes north and east.


Models remain in very good agreement regarding the timing and
placement of large scale synoptic features such as the strong low
tracking towards the central Aleutians today and the accompanying
strong system lifting into the Southern Bering. Therefore,
forecast confidence is high regarding the winds accompanying the
front and in the timing of the onset of precipitation. Forecast
challenges remain however regarding the timing of precipitation
type transitions and the amount of snow which will fall prior to
switching to rain in the Aleutians and Alaska Peninsula.

For Southcentral Alaska, the main weather features through the
rest of weekend are small and subtle troughs rotating through the
area, thus challenging forecast models regarding the placement
and duration of snow showers. Models come into much better
agreement Sunday night and Monday with forecast confidence
increasing as an incoming frontal system pushes into the
southwestern Gulf.


PANC...While occasional light snow is still possible this morning
as well as a few isolated patches of fog or low clouds, VFR
conditions are expected to prevail through early afternoon.
Another weak disturbance will lift north across the area this
afternoon and evening bringing the MVFR snow showers with it.



The Anchorage sounding this morning shows once more a fairly
decent lapse rate at mid levels which indicates an atmosphere
favorable for convective showers. However, the sounding also
indicates a general drying trend particularly through mid levels.
As a result, showers have become much weaker during the
early morning hours with generally only flurries occurring. A weak
wave will provide support for showers over the east Kenai
Peninsula and Anchorage Bowl by this afternoon and evening.
However, due to less available moisture and weak upper level
forcing precipitation should remain light.

By Monday a strong front will push into the Gulf of Alaska
supporting another round of precipitation and gusty winds.
Recent models have trended stronger along the north Gulf Coast and
storm force winds are possible. The most uncertain aspect of this
system is the amount of warm air it will pull northward. If enough
cold air remains in place, moderate to heavy snow would occur
again across the eastern Kenai Peninsula Monday night into
Tuesday. However, it is also possible that enough warm air will be
present to limit snowfall totals and result in heavy wet snow.


Clear and cold temperatures will continue throughout the Southwest
Mainland until late tonight when the front over the Bering will
begin to make landfall over the Bristol Bay coast. There is still
some question in how much snow will spread inland, especially
into the Kuskokwim River Valley and Delta. Further to the south
however confidence has improved enough for a Winter Weather
Advisory for Snow and Blowing Snow to be issued for Western
Bristol Bay on Monday. The primary concern from this will be from
the gusty northerly winds that will develop ahead of the front as
the heaviest snow begins on Monday morning. Due to the dry and
easily transportable nature of this snow event, visibilities
should begin to fall to one-half mile in falling/blowing snow on
Monday. Further to the east in Bristol Bay, downslope winds from
the Aleutian Range will largely prevent snowfall from reaching the
ground and allow temperatures to rise well into the 20s.


Most of the focus over the Bering will continue to be centered
around the developing hurricane force low spreading into the
Central Aleutians. ASCAT passes overnight confirmed widespread
storm force winds along the front, which will strengthen to
hurricane force as it spreads into the Central Bering/Eastern
Aleutians. The big question is how much warm air will spread into
the Eastern Aleutians and AK pen with the front, leading to uncertainty
in the potential for blizzard conditions in those areas. This is
especially apparent over the Eastern Aleutians which will see the
strongest push of warm air, however based on recent observations
at Dutch Harbor it appears the temperatures will remain cold
enough for at least a few hours of blizzard conditions this
morning before temperatures rise to near or above freezing. Once
blizzard conditions improve late this morning high winds will
continue with a warm/wet snow into the afternoon, so the Blizzard
Warning was allowed to continue into the afternoon (even though
visibilities will likely rise above one-quarter mile).

Over the AK pen conditions look less favorable for widespread
high winds as the front begins to fall apart, so the Winter Storm
Watch was replaced with a Winter Weather Advisory for Snow and
Blowing Snow beginning this afternoon. This front will bring areas
of visibilities less than one-half mile in falling/blowing snow
due to strong southeasterly winds with significant new snowfall.
However with southeasterly flow and warm air advection, there is
good confidence that widespread areas of blizzard conditions will
not develop.

Confidence in blizzard conditions over the Pribilof Islands is
much greater, especially now they models have trended slightly
further to the south with the front, leaving enough cold air for
even Saint George to remain as snow with strong east winds. With
up to 8 inches of new snowfall, strong winds, and temperatures
remaining below 30 degrees, blizzard conditions appear very likely
throughout the Pribilofs beginning this afternoon.


.LONG TERM FORECAST (Days 3 through 7)...
The longwave trough located over the Bering extending across the
Aleutian Chain into the North Pacific Ocean is the main synoptic
feature this upcoming week. As this feature moves eastward it
becomes negatively tilted as it moves over the Gulf by Wednesday.
This coincides with the strong meridional south to north jet
streak tracking into the Southeast Panhandle by Tuesday. This
pattern remains intact through next weekend. Therefore, look for a
warming trend with the southerly flow influencing the Gulf, and
extending through the Southcentral Alaska region. Look for the
temperatures to rise above freezing by the midweek time-frame
through the weekend. This results in abundant moisture streaming
into the Southcentral region resulting in a wintry mix along the
coastal communities. While the interior sets up with a better
scenario for moderate snowfall in favored mountain regions.
Meanwhile, the models continue to struggling with the complex low
in the North Pacific Ocean as it tracks eastward along the Eastern
Aleutians by Tuesday. As this system moves farther eastward into
the Gulf by the weekend the models have discrepancies with the
strength and timing with this feature. Therefore, the forecast
confidence is below average. Otherwise, the Bering will be under
northerly flow resulting in a showery regime heading into the
weekend. While the jet stream remains below the Aleutian Chain, it
keeps systems just south of the Chain before tracking into the


PUBLIC...Blizzard Warning 185 191 195.
         Winter Weather Advisory 181 161.
MARINE...Gale 130 131 132 150 160 176 180 181 185 351 352.
         Storm 155 165 170 171 172 174 179 411 412 414.
         Hurricane Force Wind 173 175 177 178 413.
         Heavy Freezing Spray 121 127 130 138 160 165 179
            180 185 412 414.



LONG TERM...PD is the U.S. government's official web portal to all federal, state and local government web resources and services.