This is the level most commercial airlines fly. It's also the best level to examine the location of the jetstream...the river of fast moving upper level winds that help transport high and low pressure systems across the country from west to east. Remember troughs are generally associated with cooler temperatures and unsettled weather, while ridges are conducive to warmer temps and fair, dry weather. This forecast map shows us the trough/ridge pattern and jet streaks. These streaks are locations of fast moving air embedded within the jetstream itself. Some of these jet streaks can move as fast as 150 knots and certain parts of them contribute to rising and sinking air. The locations that force rising air are associated with upper level divergence. Air that diverges in the upper level creates a vacuum at the surface and therefore must have air converging at the surface. This contributes to rising air, lower air pressure, and the formation of clouds and precipitation. Sometimes these streaks also aid in the development of severe weather because of the added "lift" in the atmosphere. Locations of a jet streak that promote sinking air have upper level convergence associated with them. Air that converges in the upper level must go somewhere...and it can't rise...so it's forced to sink. That creates a dry atmosphere and generally fair weather.