Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
756 PM EDT Tue Oct 15 2024
Valid 12Z Sat Oct 19 2024 - 12Z Wed Oct 23 2024
...Overview and Guidance Evaluation/Preferences...
The weather pattern across the Alaska domain begins with surface
high pressure over the interior as a Gulf system moves inland
along Southeast and western Canada. This should keep precipitation
initially limited to Southeast as we enter the weekend, with
amounts also trending downward with time. Cold weather is likely
for most of the state into the weekend, especially within the
interior, before a milder trend early next week as warmer air
flows northward ahead of a Bearing Sea system. This system will
likely spread precipitation chances inland for much of the
interior in the Monday-Tuesday time frame following the tranquil
weekend.
The latest 12Z/00Z model guidance is in relatively good agreement
into the weekend, with the deterministic guidance showing a system
departing the Gulf of Alaska inland. This is followed by
upper-level ridging moving over the mainland ahead of what will be
the main story through the period, a deep upper-level low over
eastern Russia that begins to move east over the Bering Sea by
early Monday. The 12Z GFS/ECMWF remain in good agreement through
Monday morning depicting initial upper-level energy ejecting over
the Bering Sea and an accompanying surface frontal system moving
inland along the western coast, while the CMC shows the streams
splitting with a much more aggressive second wave further
southwest over the western Aleutians. The CMC also takes this lead
wave east much faster over the mainland compared to the GFS/ECMWF,
with both depicting a slower but still progressive solution. The
GFS/ECMWF begin to exhibit more significant phase differences by
Wednesday as the ECMWF shows a more amplified second short-wave
compared to upper-level ridging building over the Bering Sea in
the GFS. The GFS has shown more run-to-run variability compared to
the ECMWF, with the prior 00Z solution being more amplified but
more similar in phase to the 12Z ECMWF. The 00Z ECens was not
available to use in the blended forecast, but fortunately the 12Z
GEFS mean showed a similar overall pattern to the 12Z GFS/ECMWF
and 00Z ECens through Tuesday, with details becoming less clear by
Wednesday.
The updated WPC forecast blend for the period included a split of
the 12Z GFS/ECMWF/CMC given good early agreement. The CMC
contribution is removed mid-period as the solution begins to
diverge from the other guidance and is replaced by a contribution
from the 12Z GEFS mean. The GEFS mean contribution is steadily
increased for the latter part of the period and the GFS reduced
given the greater similarity of the ECMWF to the ensemble means
and the greater run-to-run variations in the GFS as details become
less clear by Wednesday.
...Weather/Hazards Highlights...
A quieter weather pattern is expected across most of the mainland
for the weekend with high pressure in place. There will likely be
some lingering heavier showers and mountain snow for Southeast
Saturday as a low pressure system from the Gulf passes through the
region, though amounts should be trending downward with time.
Elsewhere across the mainland, mainly dry conditions can be
expected through early Sunday. Some gusty gap winds will be
possible in the presence of northerly flow along the Alaska
Peninsula east to Kodiak Island and the Kenai Peninsula.
Conditions will change by late Sunday/early Monday with warm air
advection ramping up ahead of a Bering Sea system which will
increase coastal rain, interior rain/snow, and mountain snow
prospects through at least Tuesday, perhaps lingering into
Wednesday, with the guidance in good agreement in depicting a
period of widespread unsettled weather. Higher elevations may see
over a foot of snow through Wednesday, especially for the Brooks
Range. Some gusty winds are also likely for western portions of
the North Slope/Brooks Range southward along the western coast
Sunday night into Monday as the system passes through, potentially
over 40 mph at times.
Temperatures will be rather chilly across most of the state this
weekend, with more of an Arctic air mass place. Daytime highs
will likely be below freezing for most inland areas Saturday and
Sunday, and mid 30s to low 40s along the western and southern
coasts. Warm air advection ahead of the next Bering Sea storm
system is expected to result in milder conditions by early next
week with highs rebounding by 10-20 degrees for most locations.
Putnam
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart 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