Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
403 PM EDT Sat May 18 2019
Valid 12Z Wed May 22 2019 - 12Z Sun May 26 2019
Models continue to present chaotic and disparate solutions in
terms of the pattern across Alaska during the extended forecast
period. A broad upper-level mean trough is expected to be in place
on Wed near/south of the Aleutians, with shortwave energy
traversing southwesterly flow on the east side of the trough into
the Gulf of Alaska and a mainland Alaska. Timing differences exist
even early in the period with respect to these smaller-scale
waves. Through time, differences only amplify. Major differences
emerge by the middle of next week as to whether upper riding
builds north across the Gulf toward mainland Alaska, or remains
weaker allowing mid/upper-level height falls to slide east toward
the Gulf. Most deterministic models have waffled between the two
scenarios, while ensemble means seem to provide at least
marginally consistent support for keeping a somewhat stronger
ridge (which is also consistent with forecast continuity). Given
low confidence and the high degree of run-to-run variability,
opted to stick close to continuity, incorporating the 12Z FV3 and
06Z GFS along with ECENS/GEFS ensemble means. Ensembles comprised
a majority of the forecast blend starting on day 5 (Thu), with
gradually increased weight through time.
Ryan
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