Slope and Valley Winds

Winds in mountain topography are extremely complex. Part of the time, the general winds associated with larger scale pressure systems dominate the surface layer. But when larger scale pressure systems weaken, the general winds lessen. Then, in the presence of strong daytime heating or nighttime cooling, convective winds of local origin become important features of mountain weather. These conditions are typical of clear summer weather in which there is a large diurnal range of surface air temperatures.

General and convective winds may displace, reinforce, or oppose each other. Their relationship to each other can change quickly, often with surprising rapidity. Variations between different terrain features--sometimes separated only by yards--are often noted. The convective activity may dominate the observed surface wind in one instance, and in another it may permit the speed and direction of winds aloft to dominate the surface flow through the mixing process.

The interactions between airflow of different origins, local pressure gradients caused by non-uniform heating of mountain slopes, and the exceedingly complex physical shapes of mountain systems combine to prevent the rigid application of rules of thumb to convective winds in mountain areas. Every local situation must be interpreted in terms of its unique qualities. Wind behavior described in this section is considered typical, but it is subject to interruption or change at virtually any time or place.

Differences in air heating over mountain slopes, canyon bottoms, valleys, and adjacent plains result in several different but related wind systems. These systems combine in most instances and operate together. Their common denominator is upvalley, upcanyon, upslope flow in the daytime and downflow at night. They result from horizontal pressure differences, local changes in stability that aid vertical motion, or from a combination of the two.

• Slope winds
• Valley winds
• Effects of Orientation and Vegetation on Slope and Valley Winds
• Interaction of Slope and Valley Winds With General Winds