Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
602 PM EST Wed Feb 12 2020
Valid 12Z Sun Feb 16 2020 - 12Z Thu Feb 20 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 or across southern
mainland 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. A
weakening low pressure system across the Gulf of Alaska on day 4
(Sun) showed relatively good consensus among the guidance. Farther
west, a significant low pressure system appears likely to pass
near the Aleutians into the southern Bering Sea Sun-Mon, and into
southern mainland Alaska by Tue. The ECMWF/CMC showed the best
consensus with ensemble means surrounding this system, while the
GFS persisted in taking a fairly strong leading low pressure area
north along the western mainland coast Mon (an idea with
relatively little ensemble support). Guidance shows general
consensus that another similar deep low pressure system is likely
to pass near the Aleutians by the middle of next week, with above
average ensemble clustering given the time range under
consideration. 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, although some slight
moderation of cold temperatures across the interior is possible
with southerly mid/upper-level flow early next week before the
region once again falls under the influence of arctic flow by the
middle of next week.
Heavy snow is expected across southern mainland Alaska and perhaps
portions of the interior Sun night into Tue as the deep low
pressure system traverses the region. Heavy precipitation will
also be possible across much of the Panhandle in association with
this system. The next low pressure system toward the middle of
next week will bring another round of widespread precipitation
from the Aleutians east across southern mainland and Southeast
Alaska, with heavy precipitation possible for some areas.
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.
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, Tue-Wed, Feb 18-Feb 19.
- Heavy snow across portions of mainland Alaska, Sun-Tue, Feb
16-Feb 18.
- Much below normal temperatures for parts of mainland Alaska,
Sat-Wed, Feb 15-Feb 19.
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