Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 PM EST Sat Mar 09 2019
Valid 12Z Wed Mar 13 2019 - 12Z Sun Mar 17 2019
Predictability across Alaska is slightly above average during the
early portion of the extended period (Wed-Thu), and near to
slightly below average by the latter portion of the period.
Confidence is relatively good with respect to the large scale flow
pattern across the region, with persistent mean upper-level
troughing near the Aleutians, and an upper ridge axis rebuilding
across western/northwestern Canada, into portions of mainland and
Southeast Alaska by late in the period. This setup will keep the
preferred storm track near/south of the Aleutians and into the
Gulf of Alaska, with persistent southerly flow into Alaska.
Models/ensemble members showed good clustering surrounding a
relatively strong low pressure system entering the Gulf Wed and
then moving onshore in the Alaska Peninsula or southern mainland
Alaska by Thu. By later Thu this system should weaken as it moves
inland and merges with a broader area of shortwave energy farther
north. The forecast during days 3-4 was based heavily on a blend
of the ECMWF/CMC solutions, which showed relatively good consensus
during this time frame, and maintained good forecast continuity.
In the wake of this Wed-Thu system, the flow becomes a bit more
chaotic, with a couple smaller scale shortwaves expected to skirt
south of the Aleutians and eventually move into the Gulf. Models
suggest some consolidation of shortwave energy into a closed low
south of the Aleutians by next Fri-Sat, likely associated with
another deep surface low. Additional uncertainty arises in the
handling of a couple areas of arctic shortwave energy exiting
eastern Siberia during the middle to latter portion of next week,
and whether they amplify across the Bering Sea or remain confined
closer to eastern Russia as a consolidated upper low. Given the
increased spread, the forecast was trended toward heavier ensemble
mean (ECENS/NAEFS) on day 6 (Fri), with majority ensemble means
during days 7-8 (Sat-Sun).
Ryan
Bullet points from the WPC Days 3-7 Hazards chart:
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 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