Mesoscale weather processes fall between synoptic scale and microscale; typically between a few nautical miles and a few hundred nautical miles in size, and lasting minutes to days. There are several mesoscale phenomena that may produce convergence: ### Sea Breeze As a **sea breeze** develops and pushes inland, a line of convergence forms along its boundary. The speed of the sea breeze progression inland, along with the difference in temperature between the sea breeze and inland air mass, will determine the strength and organization of the convergence line. ![[seabreeze convergence.png]] ### Anabatic and Katabatic Winds During periods of intense solar heating, **anabatic winds** such as a **valley breeze** may form and produce a line of convergence at the top of rising terrain features. ![[valley breeze convergence.png]] Conversely, when solar heating has ceased for the day, **katabatic winds** such as a **mountain breeze** may form and produce an area of convergence, particularly in narrow valleys. ![[mountain breeze.png]] ### Terrain Effects When wind flows around terrain features, an area of confluence, or a **lee convergence line** may form downwind. In addition, complex terrain features such as individual peaks, spurs, passes, etc may produce areas of localized convergence, dependent on the wind speed and direction. ![[terrain convergence.png]] ### Synoptic Effects Synoptic scale flow and weather patterns can be greatly influential to the development of mesoscale convergence phenomena. Synoptic winds may enhance or suppress the development of sea breezes and anabatic/katabatic winds, and may be the driving force behind a lee convergence line or other terrain-induced convergence zone. ### Example: Elsinore Convergence Zone The Elsinore convergence zone, one of the most famous sites for convergence soaring in the US, is a product of sea breeze interactions and terrain effects, than can be enhanced by synoptic flow. ![[elsinore convergence zone.png]]