Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
620 PM EST Mon Mar 02 2020
Valid 12Z Fri Mar 06 2020 - 12Z Tue Mar 10 2020
...Overview and Guidance/Predictability Assessment...
Upper pattern will transition toward some intermediate ridging
before troughing from the Bering Sea moves through early next
week. This will be forced by very strong upper ridging south of
Kamchatka next Mon/Tue as the ECMWF ensemble mean forecasts 500mb
height anomalies over +3 sigma which is quite high for a 7-8 day
lead time. The 12Z models clustered fairly well with the
multi-center ensembles more or less through the period, with two
main systems of interest.
The first system will be a surface low in the Bering on Friday
dropping southeastward as high pressure retreats from the
Interior. Weak system to the north across the Bering Strait should
be of little consequence as its upper support dissipates. Though
the 12Z GFS/GEFS were a bit slower aloft south of 70N, they were
quicker with the sheared northern part compared to the
ECMWF/Canadian/UKMET which had a more consolidated shortwave.
Minority weighting of the GFS (20%) was included given its
acceptable forecast for the rest of the domain.
Next system in the Bering will be right behind the first one,
moving through this weekend into southwestern Alaska then the Gulf
next Monday. After an odd 06Z run, the 12Z GFS again clustered
well with the ECMWF/Canadian and a blend with the ensembles formed
a good starting point for next Sun/Mon as the main sfc low moves
across Southcentral but the triple point skirts across Kodiak and
near the Kenai Peninsula. Progressive upper flow should keep the
system moving steadily into the Panhandle and BC.
...Weather Highlights/Threats...
Aside from generally lighter rain/snow over the Aleutians to start
the period, a realtively dry Saturday over the state will given
way to increased rain/snow to the Aleutians and southwestern areas
later Saturday into Sunday as the next Bering system moves east.
Modest snow should overspread Southcentral Sunday near the low
pressure track with increased moisture focused over the Panhandle
by Monday before diminishing Tuesday. This could be locally
heavier with enahanced moisture convergence squeezed between the
main low and the sfc high to the south, but it will be fighting
against a loss of subtropical connection back to the southwest.
Temperatures will be trending milder from intially 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.
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 and
mainland Alaska, Sun-Mon, Mar 8-Mar 9.
- Heavy snow across portions of mainland Alaska, Sun-Mon, Mar
8-Mar 9.
- Much below normal temperatures across portions of mainland
Alaska, Thu-Sat, Mar 5-Mar 7.
- Much below normal temperatures across portions of mainland
Alaska, Thu-Fri, Mar 5-Mar 6.
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