The presence of a jet stream passing over a mountain range tends to reinforce a mountain wave system that has developed at lower levels. This reinforcement provides the optimum conditions for the mountain waves to extend up to the level of the key stream.

A deep, stable layer combined with a consistent, strong, westerly flow at low level over a mountain range can result in a mountain wave system developing un to high level, when the decrease in air density with height is matched by a similar decrease in wind speed with height.

When winds from a consistent direction, approximately perpendicular to a mountain range or high plateau, increase in speed with height within a deep, stable layer, mountain waves and their effects can extend from low to high level.

A strong westerly airflow that increases in speed with height, when combined with a deep, unstable layer in the vicinity of a mountain range, can often result in the wave motion, and its associated turbulence, extending from low through to high level.

0.65°C per 100m.

0.5°C per 100m.

0.6°C per 100m.

1°C per 100m.

Latitude/longitude and vertical data (height or pressure).

Latitude and longitude data.

Latitude/longitude and time reference data.

Pressure altitude data.

FL130

FL120

FL160

FL110

True altitude is increasing

True altitude remains constant.

True altitude is decreasing

A right drift.

latitude 55°N: FL250 in winter, FL350 in summer.

latitude 55°N: FL250 in winter, FL400 in summer.

latitude 55°N: FL500 in winter, FL250 in summer.

latitude 25°N: FL500 in winter, FL250 in summer.

The increased stability and reduced convection likely decreased the upper limit of the turbulent friction layer to below 2000 ft on the early morning cross-country flight.

The strong nocturnal inversion present in the early morning most likely stopped turbulence and wind shear.

The low-level winds at night, and in the early morning, are usually much stronger and more laminar compared to those in the afternoon.

In the early morning, the changes in stability and the lighter winds lift the friction layer to well above 2 000 ft.

the actual temperature is higher than the standard temperature.

the actual temperature is lower than the standard temperature.

the elevation of the aerodrome is equal to 0 ft.

the actual temperature equals the standard temperature.

cold front turns into an occlusion.

polar air substitutes the warm air.

warm front has passed.

cold front has passed.

6370 ft

4720 ft

5220 ft

6780 ft