Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
234 PM EDT Sat May 04 2019
Valid 12Z Wed May 08 2019 - 12Z Sun May 12 2019
Today's models and ensembles still show a blocking pattern through
the middle of next week with a high amplitude Bering Sea trough
extending across the Aleutians into the north Pacific and
resultant high amplitude ridge across the northeast Pacific and
southeast Alaska.
Towards the end of next week, the models start to diverge with the
number and placement of vortices rotating around the Bering Sea
trough and resultant placement of lows in the Bering and adjacent
western AK.
The 06z GFS and 00z ECMWF show a deep cyclone developing over the
northeast Pacific 00z Fri that then moves north onshore later Fri
to early Sat. The 00z Canadian lagged several hours behind the
GFS/ECMWF, with enough spread in the ensembles to support a weaker
system.
Next weekend, the spread among where low pressure develops over
the Bering Sea, northeast Pacific and adjacent southern/western AK
grows large, with confidence plummeting due to little overlap of
where low pressure centers are located next weekend. Also, the
ECMWF and GFS have made significant run to run changes.
Consequently, preferred to rely on a consensus of the 12Z GFS/00Z
ECMWF and their ensemble means given the lack of agreement.
Temperatures will be warmer than normal over southeast AK through
most of the upcoming week due tot he strong upper ridge and
corresponding warm temperatures that remain well above normal.
Precipitation will focus over the southern coastal areas Wed-Thu,
with low pressure along the west coast fostering showers moving
inland.
Locally heavy rain may be possible in upslope locations. The rain
may redevelop over the upper Aleutians to Kodiak Island and
southwest AK Fri into the weekend if the stronger lows in the 00z
ECMWF and 06z GFS verify, as well as the 12z GFS.
Petersen
Bullet points from the WPC Days 3-7 Hazards chart can be found 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