Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 180040

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
440 PM AKDT Wed Apr 17 2019


The main upper level feature is a low siting over eastern Norton
Sound with broad cyclonic flow encompassing much of the mainland.
This feature has spread cold over western Alaska and Cook Inlet
to the MAT-SU Valleys corridor. Additionally, this upper center
is helping to support a broad north to south deformation zone
which extends from the Kenai Mountains, across the Chugach
Mountains (including the Anchorage Bowl), to over the Talkeetnas.
This zone brought significant accumulating snowfall to higher
elevations of the Chugach Mountains to Hatcher Pass and lesser
amounts at the lower elevations. Out west, cold advection and a
series of upper waves continue extensive cloud cover, snow
showers, and locally gusty winds across western Alaska and the
Bering Sea/Aleutians.



Models are in fair agreement in the overall synoptic fields in
the short term. The main difference in the upper levels is that
the GFS/NAM move the upper low center over Cook Inlet Friday
afternoon. The ECMWF/CAN NH tend to hold the main upper low
center over western Alaska. Otherwise, general surface pattern
seems to be similar.


PANC...Snow will bring IFR and MVFR conditions through the
afternoon. Conditions will improve by mid evening bringing
generally light winds with low VFR conditions (3500-5000 ft
ceilings) the rest of the night through Thursday.



A deformation band that set up over Southcentral has brought a
prolonged period of precipitation for Southcentral today. With
temperature profiles hovering around the rain/snow line, some
areas saw several inches of accumulation, with a foot or more
falling in the mountains. This deformation zone is moving very
slowly to the west as it weakens, so precipitation is tapering off
across the area, with another inch or so expected to fall through
the evening.

Tomorrow will bring a brief break across Southcentral, but colder
air aloft lingers just off to the west and is expected to make its
way up Cook Inlet beginning tomorrow evening. This will be
accompanied by an upper level low currently positioned over
Southwest Alaska, so a return of precipitation is expected
Thursday night. With the colder temperatures aloft as well as at
the surface, this may start out as a mix but then rapidly
transition to all snow. It is a drier air mass, so the snow won`t
linger quite as long as the current event. However, there are some
differences in how the models bring in the upper level support,
with the NAM being the most aggressive. Right now the forecast is
for another inch or two in the lower elevations, with 3 to 5 in
the upper elevations, but if the upper level support does move
overhead, amounts could increase as the snow lingers into the day
on Friday.


through Friday)...
Expect very little change in weather over Southwest Alaska through
Friday. An upper level low sitting just to the north will drop
southward to Bristol Bay Thursday night, then begin to lift back
northward on Friday. Showers and gusty winds will be confined
primarily to the Kuskokwim Delta coast and Western Capes,
generated as cold air moves over the relatively warmer waters of
the Bering Sea. The rest of Southwest could see some flurries or
an occasional light snow shower. As the upper low begins to lift
northward, expect steady light snow to develop along the west side
of the Alaska Range and westward into portions of the Kuskokwim
Valley. The best chance of accumulating snow will be near the
Alaska Range, with less as you head westward into the Kuskokwim


through Friday)...
A series of upper level short-waves will drop south across the
Bering Sea, Aleutians, and southern Alaska Peninsula through
Friday. These waves will help focus snow showers and stronger
winds. In particular, upslope flow along the Eastern Aleutians
and southern Alaska Peninsula will enhance snow showers.
Otherwise, mostly cloudy skies and seasonable temperatures will
prevail across the region.


.MARINE (Days 3 through 5)...Broad north winds will persist over
the Bering and Aleutians through Saturday, while a low will start
developing in the northern Pacific and trek into the Gulf. While
there is uncertainty in the exact track of the low, confidence is
growing that there will be gales in the northeastern Gulf late
Saturday into Sunday. In addition, cold air from the Bering
wrapping into the low will bring potential for gales on the back
side of the low. If the low takes a westerly track, this would
mean gales just south of Kodiak Sunday into Monday.


.LONG TERM FORECAST (Days 3 through 7)...The long term will begin
relatively quiet, with high pressure over the western Bering and
steady north flow between that high and a developing low in the
northern Pacific. Thus, expect benign conditions in the Bering
and Aleutians with possible showers in cold air advection. Over
the mainland, a weakening low over Southwest will maintain weak
onshore flow and scattered showers over the Bristol Bay area. Wet,
cloudy weather will trend wetter and cloudier throughout the
weekend along the north Gulf coast in steady southerly flow ahead
of the North Pacific low.

The forecast becomes challenging Sunday into Monday, due to
uncertainty in the track of the North Pacific low. Some solutions
point to a more northeastward track, which would be favorable for
precipitation in the Anchorage bowl, while other solutions have
the low heading farther west, which would diminish precipitation
chances in Anchorage, and increase Turnagain Arm winds. In any
case, showers will continue in the Gulf and the north Gulf Coast
through early next week. Meanwhile, steady north flow and cold air
advection showers will persist over the Bering and Aleutians
through early next week, with a series of shortwaves or embedded
closed lows periodically increasing precipitation rates. The
leading occluded front associated with the low will enhance
potential for precipitation over Southwest by Monday as it lifts
northward. As cold air continues wrapping around the west side of
the low, we may see a transition to a rain/snow mix over the Gulf
Monday, though warm sea surface temperatures may offset the cold
air. Wet, unsettled weather will continue through mid-week, but
significant impacts are not expected.




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