Refer to figure.
Mountain waves (also called orographic waves) are atmospheric oscillations that develop on the lee side of mountain ranges when two specific conditions are simultaneously met: 

• Stable atmospheric conditions
• Strong wind blowing approximately perpendicular to the mountain ridge

The waves can extend from the mountain crest to the stratosphere and span hundreds of kilometres downwind. Within the wave system several hazards are present: 

• The rotor zone → severe turbulence at low level beneath the first wave crest
• Lee slope downdrafts → can greatly exceed aircraft climb performance
• Wave crests → where lenticular clouds form and moderate to severe turbulence may occur

A mountain wave turbulence is to be expected → CORRECT. Mountain waves form when stable air is forced over a mountain ridge by a strong wind. The resulting lee-side oscillations produce turbulence, particularly in the rotor zone at low level and in areas of strong wave activity. This is the correct and expected consequence of the conditions described.

A thermal updraft is to be expected → INCORRECT. Thermal updrafts result from surface heating causing parcels of air to become buoyant and rise convectively. They require unstable conditions, which is the opposite of the stable conditions stated in the question.

A stationary front will form → INCORRECT. Fronts form at the boundaries between air masses of different temperature and moisture characteristics. They are synoptic-scale features driven by large-scale pressure patterns and temperature gradients. A local mountain range does not cause frontal formation on its lee side in the scenario described.

A high-pressure cell will develop → INCORRECT. While slight pressure variations can occur in the lee of mountain ranges, a high-pressure cell in the meteorological synoptic sense does not develop as a result of stable strong winds flowing over a mountain range. High-pressure systems are large-scale features associated with subsiding air in anticyclones, not with orographic flow.