Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
548 PM EST Wed Feb 05 2020
Valid 12Z Sun Feb 09 2020 - 12Z Thu Feb 13 2020
Models/ensembles show general consensus that an upper-level ridge
axis across the North Pacific will gradually build northward
across Alaska through the extended forecast period, perhaps
weakening to some degree by the middle of next week in response to
strong incoming shortwave energy in the westerlies. The dominant
storm track will be across the Aleutians and north into the Bering
Sea. The 12Z ECMWF/CMC showed relatively good consensus through
the first half of the forecast period, with a surface low crossing
western mainland Alaska Sat night/Sun, and precipitation spreading
across portions of the Interior. Farther east, another relatively
weak wave of low pressure should move along a lingering frontal
boundary in the Gulf of Alaska Sun night-Mon, bringing a round of
precip to the Panhandle/Southeast Alaska. After that - the storm
track shifts west, with most guidance showing a relatively deep
low pressure system crossing the western Aleutians/Bering Sea Mon
night-Wed (potentially a couple waves of low pressure, although
the finer scale details remain difficult to resolve given the time
range). This system is forecast to be relatively deep (likely
below 980 hPa), resulting in the potential for strong/high winds
across portions of the Aleutians Mon-Tue. Strong warm advection
ahead of this system should spread additional precipitation across
the Aleutians/Alaska Peninsula and into portions of western
mainland Alaska. Models show yet another similar low pressure
system approaching the western Aleutians by late next Wed/early
Thu. Model differences on track/timing were a bit higher both of
these systems, so gradually increasing emphasis on ECENS/GEFS
ensemble means by that time helped smooth out some of these
differences toward a consensus solution. Given these
considerations, a blend of the 12Z ECMWF/CMC was used initially on
day 4 (Sun), with a gradual trend toward heavier weighting of
ensemble means each consecutive day, and a majority ensemble means
after day 6 (Tue).
Additionally, with the building upper-level ridge, temperatures
are forecast to warm to near or above average across much of the
state - the North Slope being the significant exception where
colder conditions should linger at least through early next week
before perhaps some moderation by midweek.
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, Sat, Feb 8.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun, Feb 9.
- High winds across portions of mainland Alaska and the Aleutians,
Sat-Mon, Feb 8-10.
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