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As fall arrives, the jet stream starts moving south, creating more cross-barrier flow over the mountain ranges of the US. The next time you fly near mountainous or hilly terrain, look for these indications of mountain wave activity.

1) Pitch Oscillations

Mountain waves, like any wave, have troughs and ridges. As you encounter a mountain wave, your aircraft will pitch up as you fly into the ridge, and pitch down as you fly into the trough. Depending on the strength of the wave, your oscillations can range from minor pitch oscillations, to pitch changes in excess of 7.5+ degrees.

2) Airspeed Oscillations

As your pitch changes, your airspeed will also change. As you approach a ridge, your aircraft pitches up, causing your airspeed to bleed off a few knots. The opposite happens as your aircraft enters a trough and pitches down. Depending on the severity of the mountain wave, the changes in airspeed could range from 2-3 knots in light wave, to 15+ knots in stronger mountain waves.

3) Cross Barrier Flow

Mountain wave formation is most likely when the winds aloft are traveling at fast velocities, perpendicular to a ridgeline. The next time you are flying, take a look at the wind direction and speed readout on your aircraft and compare it to the ridgelines you plan to cross. This can help you assess the likelihood of mountain waves forming along your route.

4) Wave Clouds

The easiest way to detect mountain waves before you actually experience them is simply by looking at the clouds. There are a few cloud types that are generated by the presence of mountain wave. For example, standing lenticulars or rotor clouds are a direct indication that mountain waves are present.

Have you ever experienced mountain waves? Tell us about it in the comments below!