My touring partner and I went to Pea Gravel Ridge seeking sheltered terrain to avoid the wind slab problem, but also wanted to investigate the problem by digging. The previous night had been clear and on our ascent we observed surface hoar at about 5,400 ft (see pictures). Our day started calm and sunny at 0830, by 1130 there were scattered clouds with a light wind at the ridge. We dug two hasty pits in the trees around 5,500 ft on a NE slope and didn't find instability.
We dug once on the East facing slope at treeline (about 5900 ft) just below the ridgeline. Our Weber meat thermometer read the air temperature was -0.5 degrees Celsius. A 5cm thick crust was evident 65cm below snow surface. We found a wind slab to be reactive on a compression test which confirmed the forecast problem. In detail, the results were: CTM @65cm resistant planar, CTH @100cm sudden planar. We followed this up with more tests and found an ECTP 32 @75cm (2 extra firm taps) which seemed to correspond to the crust we found, and a PST 35/100 END down 100cm.
Next, after spending hours in the snow pit with my blue book, I'm going to donate to NWAC so they can keep doing this for me.