Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
616 PM EDT Thu Mar 18 2021
Valid 12Z Mon Mar 22 2021 - 12Z Fri Mar 26 2021
...Guidance/Uncertainty Assessment...
Models and ensembles overall offer better than average agreement
for the pattern evolution and significant features for much of the
next week. The Day 4-8 (Monday-Wednesday) forecast was primarily
derived from a composite blend of well clustered guidance from the
12 UTC ECMWF/Canadian and ECMWF ensemble mean. The 12 UTC GFS/GEFS
do not match continuity as well and the soon to be operational
experimental GFS trended toward the favored composite. Forecast
spread increases by days 7/8 when a composite of the 12 UTC
GEFS/ECMWF ensemble means was mainly used along with the best
clustered guidance from the 12 UTC ECMWF to add a bit more system
detail.
Composites mitigate less predictable smaller scale differences.
WPC continuity is reasonably well maintained with this forecast
methodology in a pattern with above normal predictability.
...Weather/Hazards Highlights...
The Aleutians/AKPen should see a period of precipitation and
enhanced winds early next week on the northwest side of a
northeastward lifting North Pacific system. This maritime threat
storm will then quickly bring increasing moisture to the southern
coast and especially the Panhandle Tuesday-Wednesday where there
is the highest potential for terrain enhancing heavy precipitation
given the lower-latitude origin of the moisture.
Bering Sea upper troughing, surface system development and onshore
track may spread some organized snows into the Interior/Southwest
AK early next week, but stream interactions and continuity with
the features has been less than stellar. Subsequent system
energies slated to track across the Bering Sea would bring a front
across the southern Bering and Aleutians into midweek and again
later next week. These are expected to be accompanied by
precipitation and some brisk winds. Moderate activity is slated
with some uncertainty to progress into the western mainland and
the Gulf of Alaska mid-later week with both a lead and secondary
systems.
Schichtel
Hazards:
- No significant hazards are expected over Alaska during this
forecast period.
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
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