Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Wed Apr 18 2018

Valid 12Z Sun Apr 22 2018 - 12Z Thu Apr 26 2018

...Guidance/Uncertainty Assessment...

The 00/12 UTC GFS/ECMWF show similar larger scale pattern
evolutions at medium range time scales but have some embedded
system timing and emphasis differences days 4-8, mainly with
offshore lows. Ensemble means are reasonably compatable, but the
00 UTC ECMWF ensemble mean offers max WPC continuity with surface
system timings in between the GFS and ECMWF. Manual modifications
were applied to produce sufficiently deep offshore lows to be more
consistent with upper support than a smoothed mean. Predictability
seems slightly above average in this pattern.

...Weather/Threats Highlights...

Short range height falls dig southwestward over the interior and
leads to an ern Bering Sea closed low by Sunday that is
assimilated early next week. The system is amplified enough to
support lingering unsettled wintery weather over swrn AK.

Meanwhile, an energetic storm track flows underneath from the
north Pacific with a lead deep low to steadily track from just
south of an Aleutians/swrn AK this weekend to across the nrn Gulf
of AK Monday.This threatens maritime interests with winds/waves as
moisture wraps around the low/frontal system to combine with
terrain to fuel some srn to sern AK heavier precipitation.
Upstream, a second deep low in this series is expected to cross
the Aleutians Sun/Mon with a subsequent storm track to the
srn/sern Bering Sea Mon-next Thu that brings some risk of heavy
wind/waves/precipitation to then spread inland into wrn/swrn AK in
about a week.

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