Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 PM EST Thu Nov 22 2018

Valid 12Z Mon Nov 26 2018 - 12Z Fri Nov 30 2018

...Guidance/Predictability Assessment...

Operational models and individual ensemble members continue to
show significant spread for features within an overall evolution
depicted similarity in the ensemble means. On day 4 (Mon), there
is decent consensus among the ensemble means that a deep low will
be located somewhere over the Gulf of Alaska, perhaps just south
of the Alaska Peninsula. Deterministic solutions continue to show
a large degree of run-to-run variability with the details of this
system, showing the potential for multiple waves of low
pressure/triple point lows evolving quickly. Ensemble mean
solutions have maintained a much higher degree of consistency, and
thus they remain the preference. This system is expected to weaken
by day 5 (Tue) as the surface front pushes inland and the low
begins to fill. The active pattern continues, however, with
another system expected to track near/south of the Aleutians and
Alaska Peninsula by mid to late next week, and yet another
approaching the western Aleutians and perhaps moving into the
southern Bering Sea by late next week. The same story holds true
with these systems as with the earlier one, in that individual
model solutions show a wide degree of spread and variability,
while ensembles show a bit more consistency. Ensembles show some
consensus that the late week system nearing the Aleutians could be
a bit stronger, with even a blend of means resulting in a surface
low in the well into the 980s (hPa). Given these considerations,
this forecast maintains near exclusive focus on the ensemble
means, which yielded a forecast close to continuity.


...Sensible Weather Highlights/Hazards...

The deep low pressure system in the Gulf of Alaska Mon-Tue will
likely result in areas of heavy precipitation for coastal areas of
southern mainland and Southeast Alaska. Precipitation will fall in
the form of snow at all but the lowest elevations along the coast.
The system may also produce strong/gusty winds along the coast.
Persistent onshore flow will keep precipitation chances relatively
high across southern/southeastern Alaska through much of next
week. Precip should become more widespread across the Aleutians by
late next week in association with the next couple low pressure
systems traversing the North Pacific. Temperatures during the
extended period will generally be several degree above average
south of the Brooks Range, as the active North Pacific flow regime
will inhibit any significant incursions of arctic air farther
south.


Ryan

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
http://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html