Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
552 PM EST Tue Mar 03 2020
Valid 12Z Sat Mar 07 2020 - 12Z Wed Mar 11 2020
...Overview and Guidance/Predictability Assessment...
Upper ridging initially poking into the Aleutians on Saturday will
move eastward and flatten by next week, allowing troughing to move
through the Bering Sea. That will settle over the Interior next
Tue/Wed with another surge of colder than normal temperatures for
the mainland.
The 12Z models/ensembles were in generally good agreement to
start. Weak system will skirt the North Slope as a shallow trough
swings through. The larger system will be in the Bering Sea and
will move eastward. Its triple point will likely rush toward the
AKPEN/Kodiak then into the Gulf as (potentially) a surface wave
along the front lifts toward the old parent low and perhaps
combines/deepens near Bristol Bay/AKPEN around late Sun into Mon.
The GFS was much less bullish on this scenario than the ECMWF
(which was much more aggressive) while the UKMET/Canadian did show
a sfc wave but with development just to the southeast of the AKPEN
Monday. With a trend toward more development along the front,
opted to weight the ECMWF enough to show such an evolution but
less intense as the ensemble support was not there at this time.
It seems the ECMWF has been about a cycle ahead of the other
guidance lately but has also favored more phasing in its forecast
than reality.
By next Tue, low should move through the Gulf and into/through the
Panhandle thereafter. Ensembles were in better agreement than any
given deterministic model (though the GFS/ECMWF were aligned in
the Bering), so favored their consensus more than the GFS/ECWMF
cluster. This was a slower progression than the forecast 24 hrs
ago given the trend to have the trailing surface wave slow part of
the system down, but otherwise continue eastward steadily in wavy
zonal flow.
...Weather Highlights/Threats...
Rain/snow will increase over the Aleutians and southwestern areas
later Saturday into Sunday as the lead Bering system moves
through. Modest snow should overspread Southcentral Sunday near
the triple point low pressure track. Precipitation will then
expand across the Panhandle Monday with the lead wave then the
real cold front followed by the upper trough Mon-Wed,
respectively. Precipitation could be locally heavier with enhanced
moisture convergence but a steady loss of subtropical connection
back to the southwest. Temperatures will be trending milder from
initially well below normal values over the Interior. The
Panhandle will likely hold onto chillier temperatures longer with
enough easterly flow out of Canada through this weekend before
milder Pacific air moves in. Colder than normal temperatures will
again fill in behind the departing system over western areas next
week.
Fracasso
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 to
the coast sections of southern Alaska, Sun-Tue, Mar 8-Mar 10.
- Heavy snow across portions of southern Alaska, Sun-Mon, Mar
8-Mar 9.
- Much below normal temperatures across portions of eastern
mainland Alaska, Fri-Sat, Mar 6-Mar 7.
- Much below normal temperatures across portions of western
mainland Alaska, Mon-Tue, Mar 9-Mar 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