Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
235 PM EST Sat Nov 09 2019
Valid 12Z Wed Nov 13 2019 - 12Z Sun Nov 17 2019
Models show relatively good consensus that a deep surface low
should pass south of the Alaska Peninsula Wed-Thu as it heads
toward the Gulf of Alaska. Timing and some remaining detail
differences among deterministic and ensemble solutions make for
moderate confidence. Incorporated a blend of the latest
deterministic guidance (ECMWF/CMC/GFS) into the forecast for days
4-5 (Wed-Thu). Placed particular emphasis on the ECMWF solution
during the early extended time frame as its solution seemed very
well-centered within the model/ensemble spread. This low pressure
system could produce a variety of impacts, including the potential
for strong winds and significant waves along the coast - although
given a trend toward a more northeastward track into the Gulf
while the low is deepest, these impacts could be somewhat limited.
As this system weakens near the mainland Alaska coast by Fri, the
upper-level energy, along with additional arctic shortwave energy
arriving from the north, are forecast to linger across western
mainland Alaska or the eastern Bering Sea through late next week.
Models differ on the precise interaction between these features,
but a number of solutions continue to indicate development of an
upper low, while others depict a more disorganized scenario. South
of this upper low, a stream of small scale but quick moving
shortwaves are expected to cross near the Aleutians and toward the
Gulf of Alaska. Spread increases through time, but some consensus
was noted among ensemble means that another low pressure system
should approach southern mainland Alaska by next Fri night or Sat,
associated with one of the more significant aforementioned
shortwaves, with yet another crossing the Aleutians Sat-Sun. Given
gradually increasing spread, a trend to heavier weighting of
ECENS/NAEFS ensemble means was shown during days 6-8 (Fri-Sun).
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html