Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
607 PM EST Tue Feb 11 2020
Valid 12Z Sat Feb 15 2020 - 12Z Wed Feb 19 2020
An active upper-level jet across the North Pacific will cause a
series of relatively deep low pressure systems to progress near
the Aleutians and into the Gulf of Alaska during the extended
forecast period. Clustering of deterministic solutions and
ensemble members was perhaps a bit better than average through the
period, despite a fair degree of variability on timing/intensity
among deterministic solutions. There were some significant
intensity differences on a surface low expected to pass south of
the Aleutians and move into the Gulf of Alaska Sat-Sun, with the
ECMWF on the strong side and the GFS on the weak side, but general
agreement on timing of the system. Thus, a compromise on the
intensity of this feature between the ECMWF/GFS seemed reasonable.
The described scenario should lend favorably to relatively heavy
use of ensemble means fairly early in the extended period. Farther
north, the arctic influence across the North Slope and northern
portions of the interior looks to persist into at least the middle
of next week. A cutoff upper low is shown by most guidance to
persist across northern mainland Alaska through Sun or perhaps
into Mon before an additional arctic shortwave approaches by the
middle of next week. Models/ensemble show agreement on this
general idea, despite some differences on the specifics. This
lends further utility to a heavily ensemble-based blend. Given the
considerations, a blend based on the 12Z ECMWF/GFS was used
initially on day 4 (Sat), with a shift to heavier weight on
ECENS/NAEFS ensemble means from day 5 (Sun) onward.
The Aleutians, southern mainland Alaska, and the Alaska Panhandle
will remain subject to frequent round of precipitation during the
extended forecast period due to the frequent passage of low
pressure systems. Heavy precipitation will be possible for some
areas through Tuesday. Additionally, the arctic air mass across
the interior and the North Slope will hold strong through much of
the forecast period, with high/low temperatures 10 to 20 deg F
below average for many areas. Meanwhile, areas across the
Aleutians, southern mainland, and Southeast Alaska will see near
to even above normal temperatures due to the increased influence
of Pacific air across those regions.
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon-Tue, Feb 17-Feb 18.
- Much below normal temperatures for parts of mainland Alaska,
Fri-Mon, Feb 14-Feb 17.
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