Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
340 PM EDT Wed Apr 10 2019
Valid 12Z Sun Apr 14 2019 - 12Z Thu Apr 18 2019
There is general agreement in the guidance that a moderately
progressive North Pacific pattern should transition toward a
slower and more amplified regime, highlighted by a mean trough
around 150-160W longitude by next Wed-Thu. Supported by energy
initially just upstream from the northwestern mainland, mean
troughing may also develop along the western coast of the
mainland. Within this consensus evolution there are multiple
detail/phasing uncertainties that considerably lower confidence in
specific details. Thus while the pattern should eventually favor
increasing precipitation chances along the Panhandle and southern
coast, the precise timing and magnitude of the precipitation are
unclear.
One notable change from yesterday involves the combination of
short range upper low energy over the northwestern mainland and
initial energy over the Gulf, with latest trends leading to a more
persistent Gulf low aloft during Sun-Mon. At the same time there
has been a trend toward a more consolidated upper system reaching
the central Pacific by day 5 Mon (possibly interacting with some
lingering Aleutians energy). This ultimately leads to slower
progression of low pressure that tracks south of the Alaska
Peninsula and Kodiak Island. During the latter half of the period
a further complication comes into play with potential eastern
Siberia into eastern Bering/western mainland upper low energy
(more prominently signaled in operational guidance so far) and/or
upstream energy possibly interacting with the North Pacific trough.
Yet another significant wild card will be an initial central
Pacific wave. Some solutions like the 00-06Z GFS/00Z CMC phase it
with the upper system south of the eastern Aleutians and Peninsula
around Tue-Wed, while the 12Z GFS and faster 00Z ECMWF keep the
wave separate with a track to or just south of the Panhandle.
This wave gets lost in the means but the means do have a modest
weakness that could in theory contain a progressive wave.
Today's forecast incorporated various ideas from the models and
ensemble means in an attempt to reflect the most agreeable aspects
of the guidance while downplaying or reflecting a compromise for
more contentious details. The first part of the period tilted
somewhat more toward the 00Z ECMWF/00-12Z GFS relative to the 06Z
GEFS/00Z ECMWF means, followed by greater ensemble mean weight
later. Some NAEFS was also included mid-late period due to being
a little deeper with low pressure than the GEFS mean.
Rausch
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
- No significant hazards are expected over Alaska during this
forecast period.
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