Since winds above the Long Valley area blow toward an easterly direction more than 80 percent of the time, air routes east of the volcano are likely to be contaminated with volcanic ash during a future eruption.
For example, air routes within a few hundred kilometers east of Long Valley that accommodate jets either approaching and departing San Francisco or flying in a north-south direction toward or away from Las Vegas, Nevada.
This graph shows the average percentage of time, annually, that winds between 3,000 and 16,000 m (10,000 to 53,000 ft.) blow toward compass directions above Las Vegas, Nevada. It indicates that areas in the direction of the blue zones have a greater chance of being affected by tephra fall than do other areas. On an annual basis, the winds in the Long Valley-Las Vegas area blow toward a sector between N. 45° E. and S. 45° E. more than 50 percent of the time. The winds blow toward some easterly direction more than 80 percent of the time.