FXAK68 PAFC 190045
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKDT Mon Mar 18 2019
.ANALYSIS AND UPPER LEVELS...
A very strong ridge of high pressure is over western Canada,
keeping southerly flow aloft over the Gulf and the southern Alaska
mainland. There is an upper level low over the Alaska Peninsula
moving towards the northeast. The associated surface low is
situated just west of Cook Inlet. The front stretches from the low
eastward to near Icy Cape and then south across the Gulf.
Considerable rain and some gusty winds are occurring across the
Gulf coast area. On the back (west) side of the low it is snowing
over much of Southwest Alaska. Broad weak cyclonic flow is over
the Bering and Aleutians, with generally benign weather.
The numerical models remain in rather good agreement through
Wednesday afternoon. There are some minor differences in timing
and the exact path of a low that traverses the southwest Gulf
Tuesday night and moves roughly into the northeast Alaska
Peninsula on Wednesday. This has minimal impact on the forecast.
Therefore the forecast confidence is higher than normal.
PANC...VFR conditions will persist. Gusty southeasterly winds
will bend in off Turnagain Arm by around 03Z as a surface low
passes to the west. Gradients will rapidly weaken, but unstable
up Inlet flow will cause southerly winds to linger overnight.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Tonight
A surface low currently in southern Cook Inlet will continue to
track northward into the Susitna Valley/Alaska Range this evening
and into Interior Alaska tonight. A number of weather changes will
occur as a result. First, the Turnagain Arm and Knik Valley winds
will finally diminish and dissipate after both track north. Thus,
gusty winds will impact Anchorage this evening, persisting through
about midnight, then diminish. With the loss of the downsloping
effect of the mountains, cold air advection and the passage of a
trailing upper level wave may cause some sprinkle or flurry
activity late tonight, primarily after the winds subside. With a
slightly further west track compared to yesterday, most of the
upper level energy will stay west of Anchorage. So nothing much
more than sprinkles and flurries are expected. Finally, a colder
air mass will follow behind the precipitation for the first half
of the day Tuesday. This should result in significantly more
sunshine for the day Tuesday than most of Southcentral has seen
in quite a while, especially in the morning.
A stationary front currently sitting over the central Gulf,
pumping moisture into eastern Alaska will begin a slow westward
drift during the day Tuesday. This will result in clouds building
back in from the east, overspreading Anchorage, the Mat-Su, and
Kenai Peninsula by late in the day Tuesday. Ridging building
behind the front will also replace the The front itself is
relatively weak, but another North Pacific low is expected to
track northwestward to near the southern tip of Kodiak Island late
Tuesday night. The low will add moisture and help intensify the
precipitation along the front, along with returning the
predominant wind direction back to southeasterly. Thus, the
pattern Tuesday night and Wednesday will return right back to
where it is now, with warm air causing mountain snow, coastal
rain, and inland downsloping. Anchorage and the Mat-Su can expect
a return to occasionally windy conditions resulting in near record
high temperatures under mostly cloudy skies, with lows struggling
to return to the freezing mark each night. The March thaw continues.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A deformation band stretching from a surface low near Kamishak Bay
to the northwest across the southern Alaska Range and into the
lower Kuskokwim Valley, which has been bringing snow to interior
portions of Southwest Alaska this afternoon, will lift off to the
northeast this evening as an upper level trough over Bristol Bay
swings inland. Upper level ridging will build in over Southwest
Alaska Tuesday. A frontal band extending northwest from a low
tracking into the Southwest Gulf Tuesday night will rotate east
into Southwest Alaska on Wednesday bringing another round of snow.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Currently the Bering is located under a broad area of cold upper
level troughing extending south from a pair of arctic lows
centered over the Kamchatka Peninsula and western Chukchi Sea.
Small troughs track from west to east across the Bering with a
larger vertically stacked low moving to the east, south of the
Aleutians becoming centered south of the eastern Aleutians this
evening. The low will stall and remain in this general location
through around Wednesday when a developing north Pacific low
tracking towards the Southwestern Gulf absorbs it on its way
north. A surface low tracking east around the southern tip of
the Kamchatka Peninsula will turn northeast and track into the
far western Bering Wednesday.
.MARINE (Days 3 through 5, Thursday through Saturday)...
Confidence is still rather high that north/northeasterly gales
will develop over the eastern half of the Bering Thursday through
Friday. Gales will become more widespread on Friday and extend
south across the AKPEN and eastern Aleutians before diminishing on
Saturday. Wave heights will peak Friday afternoon over the
southeastern portion of the Bering (north side of the
Aleutians/AKPEN) approaching 20 ft. Further west, confidence
increases that a strong low will push east across the western
Bering by Friday afternoon, with winds ranging between upper end
gales to low end storms with wave heights increasing to 20-25 ft
...Gulf of Alaska...
Decent model agreement surrounding a 960 mb low moving into the
Gulf south of Kodiak on Thursday leads to increasing confidence
that gale force winds will spread across most of the Gulf through
Friday afternoon. Waves will also increase to 25 ft over the open
Gulf by Friday as well. Winds should diminish below gale force by
Saturday though a secondary low may move into the eastern Gulf
over the weekend but likely to remain mostly sub-gale force.
.LONG TERM FORECAST (Days 3 through 7, Thursday through
The warm and wet pattern looks to continue into the weekend as
upper ridging over western Canada/US will help to direct the storm
path north into the southern mainland. On Thursday morning, the
Gulf coast will see a short break before a broad 960 mb low tracks
north, with the center moving to a few hundred miles south of
Kodiak. A front moving well ahead of the low will slam into the
coast by Thursday afternoon bringing another round of heavy precip
and mountain snow to the Prince William Sound/eastern Kenai
coastline, with snow levels rising to above 2000 ft. Strong cross
barrier flow will promote downsloping on the west side of the
mountains keeping inland areas dry, while also ramping up the gap
winds through Friday, including through Turnagain Arm. The low
looks to stall out then shift south while weakening as it runs
into the upper ridge nosing into eastern interior AK.
By the weekend, a strong low pressure system tracks east into the
western Bering. This system looks to be strong enough to push the
persistent upper ridge to the east allowing the overall longwave
pattern to become more zonal (west to east) instead of
meridional (south to north). The pattern still looks to remain
rather unsettled as a parade of lows push east across the Bering
into the mainland, though specific timing and strength of these
systems is still to be determined
MARINE...Heavy Freezing Spray Warning 180 181.
Gale Warning 119 130 138 139.
SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
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