Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Fri May 17 2019
Valid 12Z Tue May 21 2019 - 12Z Sat May 25 2019
Models present chaotic and disparate solutions in terms of the
pattern across Alaska during the extended forecast period. An
upper-level mean trough is expected to be in place on Wed
near/south of the western 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 (a scenario
the ECMWF has fairly consistently shown), or ridging that remains
weaker allowing the upper mean trough to slide east toward the
Gulf (as shown by the GFS). The CMC has waffled between the two
scenarios, while ensemble means seem to provide somewhat more
support toward the ECMWF idea, which is also consistent with
forecast continuity. Thus, a blend of the ECMWF with ECENS/NAEFS
ensemble means was used as a forecast starting point on day 4
(Tue), with majority ensemble means from day 5 (Wed) onward. This
solutions depicts a slow-moving low pressure system south of the
Aleutians Wed-Thu, and nearing the island chain by Fri-Sat.
Confidence is low in the specifics of this forecast, however.
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
No significant hazards are expected over Alaska during this
forecast period.
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