Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
341 PM EDT Sat May 05 2018

Valid 12Z Wed May 09 2018 - 12Z Sun May 13 2018

...Guidance/Predictability Assessment and Preferences...

Guidance continues to cluster better than average in the mid to
latter portions of next week due to the high amplitude and slow
forward motion of systems. This bolsters the forecast to above
normal confidence levels. WPC medium range guidance was primarily
derived from a blend of the 00 UTC GFS/ECMWF days 4-6 and then the
00 UTC ECMWF ensemble mean days 7/8 amid growing forecast spread.
These 00 UTC ECMWF ensembles seem to cluster best with
deterministic model slightly less progressive trends in this time
period and offer a good midpoint for surface system positions.
Manual forecast modifications were then applied to depict deep low
pressure offshore consistent with dynamic support aloft. WPC
continuity was well maintained overall.

...Weather/Threat Highlights...

Deep layered ridging builds from NW Canada to the warming Alaskan
interior/North Slope early next week as the initial potent upper
low persists in the southern Bering Sea. This low gradually
weakens mid-later week as a triple point low forms further south
across the Gulf of Alaska then gradually lifts/weakens into the
lead ridge position, along with associated precipitation/weather
focus.

There is then a substantial later week into next weekend potential
for powerful low genesis from the northeastern Pacific
northeastward into the Gulf of Alaska with consolidation of as
deep closed trough energies/height falls. WPC progs show a deep
surface low pressure system with potential for high winds/waves
and wrapping heavy precipitation slowly tracking from the south of
the Aleutians to into the north-central Gulf of Alaska. This may
increasingly threaten southwestern/southern Alaska. 

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

Schichtel