Sea air often has a higher dewpoint than drier inland air.  As shown in  Figure 9-29 , a curtain cloud sometimes forms,  marking the area of strongest lift. Due to the mixing of  different air along the sea-breeze front, at times the lift can  be quite turbulent. At other times, weak and fairly smooth  lift is found. around one end of the ridge flows past a polluted urban  area, such as in the Lake Elsinore soaring area in southern  California. In very complex terrain, with ridges or ranges  oriented at different angles to one another, or with passes  between high peaks, small-scale convergence zones can  be found in adjacent valleys, depending on wind strength  and direction.  Figure 9-30B illustrates a smaller-scale  convergence line flowing around a single hill or peak and  forming a line of lift stretching downwind from the peak. Convergence can also form along the top of a ridgeline or  mountain range. In  Figure 9-31 , drier synoptic-scale wind  flows up the left side of the mountain, while a more moist  valley breeze flows up the right side of the slope. The two  flows meet at the mountain top and form lift along the entire  range. If clouds are present, the air from the moist side  condenses first, often forming one cloud with a well-defined  step, marking the convergence zone. For this scenario, the  better lift conditions will be found on the west side where  the air is dryer rather than the east side where clouds are  more likely to form.  Several factors influence the sea-breeze front character  (e.g., turbulence, strength, and speed of inland penetration,  including the degree of inland heating and the land/sea  temperature difference). For instance, if the land/sea  temperature difference at sunrise is small and overcast cirrus  clouds prevent much heating, only a weak sea-breeze front, if  any, forms. Another factor is the synoptic wind flow. A weak  synoptic onshore flow may cause quicker inland penetration  of the sea-breeze front, while a strong onshore flow may  prevent the sea-breeze front from developing at all. On the  other hand, moderate offshore flow generally prevents any  inland penetration of the sea-breeze front. If the sea-breeze front is well defined and marked by a curtain  cloud, the pilot can fly straight along the line in fairly steady  lift. A weaker convergence line that is not well-defined often  produces more lift than sink and the pilot must fly slower  in lift and faster in sink. Soaring pilots must be aware that  convergence zone lift can be turbulent especially if the colder  and warmer air is mixing and be prepared that flying the  thermals may be difficult at times.  As a final example, toward evening in mountainous terrain  and as heating daytime abates, a cool katabatic, or drainage,  wind flows down the slopes. The flow down the slope  converges with air in the adjacent valley to form an area of  weak lift. Sometimes the convergence is not strong enough  for general lifting, but acts as a trigger for the last thermal  of the day. In narrow valleys, flow down the slope from  both sides of the valley can converge and cause weak lift.  [Figure 9-32]  Many local sites in either flat or mountainous  terrain have lines or zones of lift that are likely to be caused or  enhanced by convergence. Chapter 10, Soaring Techniques,  covers locating and using convergence. Convergence can also occur along and around mountains or  ridges. In  Figure 9-30A , flow is deflected around a ridgeline  and meets as a convergence line on the lee side of the ridge.  The line may be marked by cumulus or a boundary with a  sharp visibility contrast. The latter occurs if the air coming  Cooler sea air Warmer inland air Curtain cloud Convergence line Figure 9-29.  Sea-breeze front. 9-20