Mount Pilchuck and Wave Flying

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Mount Pilchuck (5341 ft high and 17 miles SE of AWO) is one of the more prominent landmarks around Arlington and a favorite waypoint for Evergreen XC pilots in thermalling conditions.  It is also one of the more accessible ridge and wave flying locations available when the winds are blowing and the visibility is adequate.
Mount Pilchuck is really a NW to SE oriented ridge with a scenic lookout at the summit that is a popular hiking destination.   The SW facing side provides good ridge lift whenever there is a southwesterly wind of more than about 15 kts.  And sometimes – we don’t know exactly under what conditions – it also produces wave conditions.
The standard textbook model is for a suitable mountain in the right wind conditions to set up a downwind resonance (a “gravity wave”) with wave crests of decreasing amplitude  every 3 to 6 miles downwind of the mountain.  This is dependent on the right wind conditions and amplification and attenuation are highly dependent on various factors like air mass stability and terrain.  With the right humidity there will be a cap cloud over the mountain, lenticular clouds at the wave crests, and rotor clouds underneath.  However, wave conditions can exist with any combinations of these clouds and on Pilchuck there are usually none.  One condition we have encountered several times without fully understanding it, is a wave over Pilchuck that appears to be triggered by resonance from some of the low lying upwind ridge; in this case the ridge lift seems to continue upwards several thousand feet above the mountain, indicating wave lift on top of ridge lift.
For pilots not yet familiar with long flyouts from the mountains it is a safe bet to leave  Pilchuck at the summit height with all club gliders (except the L-23 which may need some more height over the summit) to get back to AWO in a simple glide.   And for reassurance there are the Green Valley and Frontier airfields on the way that allow easy aero retrieves.
A good example of combined ridge and wave conditions can be seen in this depiction of a flight in the Chinook on 9/25/2010 in strong SW winds.

The flight started with a tow to just short of Pilchuck.  Strong ridge lift was encountered upwind of the summit but it dwindled to almost nothing several hundred feet higher.  However, with a lot of patient back and forth flying along a half mile length an altitude of 9090 ft was finally reached (with an average climb rate of 87 fpm over 40 minutes) before the lift went to zero – clearly more than ridge lift.  After a short downwind dash the “standard” wave was found some 5 miles downwind of the summit – just over Green Mountain.  Again it took some patient back and forth to slowly climb up in the silky smooth lift.  It took 20 minutes to top out at 11, 760 ft.  This is not as spectacular as what the wave specialists use in the awesome Owens Valley wave or even the Wenatchee wave but it was a very satisfying experience.
Another nice combined ridge and wave flight was made by Brad Hill in the Tetra on 1/24/2013.  The wind was again from SW (some 25 kts at 6,000 ft) but the lift conditions were somewhat different.

 
This time the ridge lift on Pilchuck extended to about 1,000 ft above the summit with no indication of wave above and the downwind primary was located just 3 miles downwind of the Summit, almost directly over the South Fork of the Stillaguamish River.  Brad used this wave several times, the last time climbing to 9, 360 ft at an average rate of 340 fpm.  An exploratory run to Threefinger Mountain in hope of finding a secondary wave was unsuccessful.

One consideration when flying in these conditions, which are quite often prefrontal weather conditions with increasing moisture, is a safe VFR return to AWO.  Low lying cloud decks can come in and increasingly obscure the return flight path to AWO.

 
The above picture shows a condition where the incoming low cloud deck required the four pilots that were enjoying ridge soaring on Pilchuck Mountain to retreat while AWO was still visible.  But altogether windy conditions on our house mountain – especially early or late in the year, when cumulus clouds seem to have vanished - can provide interesting and rewarding flight experiences.