Scientific Forecaster Discussion
fxak68 pafc 251410
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
510 am akst Sat Feb 25 2017
Analysis and upper levels...
the pattern this morning is very similar to that which we saw Thu
morning. A closed high in the Gulf is pushing a transient ridge up
into southcentral Alaska while a warm front is spreading over the West
Coast. The upper level jet moves along the front at nearly 140 kts
before climbing up and over the ridge at 120 kts. The result is
widespread stratus and fog over much of southcentral with another
round of precipitation heading for the southwest communities.
Radar echoes are increasing on both the King Salmon and Bethel
radars. Precipitation should start as snow for most locations, but
could then see some rain mix in late as temperatures hover near
or just above freezing. The parent low for this front is way back
near eastern Russia. It is swinging storm force winds through the
western Bering and pushing a cold occlusion from the central
Aleutians through the Pribilof Islands. This cold occlusion has a
very deep moisture tap down to about 30n and it does not look to
move much today. So precipitation starts along this corridor from
Adak to St Paul, it will not stop through most of sun.
models remain in rather good agreement handling the synoptic
pattern. This results in moderate to high confidence regarding the
dominant weather features. There are still a few areas of
uncertainty at this time. One is precipitation type over the
southwest today and tonight. Models show some warmer air pushing
in today as the precipitation arrives. This should make for a very
wet snow or even a rain/snow mix. However, if precipitation rates
were heavy enough, it could bring down enough cold air and allow
precipitation type to stay snow. The next area is for
precipitation moving into the Susitna Valley and Cook Inlet region
early Sun morning. Models generally agree that not much snow will
make it over the Alaska Range, and what does should stay mostly over
the higher elevations of the mat-su valleys. But there could still
be a few snow showers over the hillside of Anchorage. Finally, in
the mid-range, there is uncertainty with the stronger shortwave
dropping from north to S across southern Alaska Mon-Tue. The American
models are stronger with this than the ec at this time. We will be
watching trends with this closely as it could bring some more snow
to southcentral. And if the stronger solutions were to verify, it
could potentially lead to a very impressive outflow event for
places like Whittier and Seward.
panc...stratus and fog continue to be an extremely tricky forecast
this morning. Building heights and some dry air should help it to
mix out entirely later today. But the precise timing of when this
happens is highly uncertain. It should be gone with the help of
the late-February sun by early afternoon. MVFR ceilings will
return this evening though ahead of the next front which could
bring some precipitation by late in the period.
Short term forecast southcentral Alaska (days 1 and 2)...
The large upper level ridge centered south of the area is putting
southern Alaska in a zonal flow pattern with a few upper level
waves moving across it the next few days. There will be some
chance of snow with each wave, but none of them look overly
impressive and many places will not see any snowfall at all. The
relatively warm airmass over Cook Inlet is keeping areas of
stratus and fog around this morning. These low clouds and fog may
persist a bit into the day for areas close to the inlet.
Short term forecast southwest Alaska (days 1 and 2)...
A warm and moist front is aimed at the Kuskokwim Delta this
morning with some strong winds. Precipitation in the Delta will
begin as snow, and then mix with rain before changing to all rain
in the afternoon. The rest of southwest Alaska will remain cool enough
for some snow. As the front moves southeast, temperatures across
the area will cool tonight and allow some snow to fall. On sun
some warming limited to the Bristol Bay zone will cause snow to
mix with rain. Sun night through Mon cold air filters into the
region, and only diminishing snow showers are expected.
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
The front extending across the area will bring rain and snow
along with small craft to gale force winds through the weekend and
Long term forecast (days 3 through 7)...
a colder pattern slowly settles back over the southern Mainland
and surrounding waters for next week. The upper level ridge
building over the Mainland this weekend, flattens out on Monday as
a strong shortwave dives from the Arctic bringing a colder air
mass to the Gulf. A new ridge quickly develops over the Bering
into Tuesday with a long wave trough stretching along the Mainland
and Gulf. Models are in relatively good agreement with this
weather regime, however they differ slightly on handling multiple
waves that eject southward from the Arctic. Only minor changes
were made in the extended forecast due to uncertainty in both
timing and placement of the anticipated waves.
Marine...Gale Warning 120...131...173...175...176...178...179...181
Storm Warning 185