Thermals are the most common form of lift utilized by glider pilots; they can form in virtually any terrain, and in any season, as long as there is sufficient solar heating to cause [[Heat Imbalances]] at the surface. Many thermals are discovered by accident or chance, however, knowing what causes [[Thermal Formation]], and the visual indications of thermals can make the search much easier. The general wisdom is: if you're up high, look for signs of thermals in the air above and around you; if you're down low, look for the sources of thermal production. ## Cumulus Cumulus clouds in the sky are the most obvious markers for thermals. ### Cumulus Lifecycle and Species ![[cumulus species.png]] As a thermal rises, it expands and cools; first at the **dry adiabatic lapse rate**, until it becomes saturated at the **convective condensation level** (CCL) where the [[Thermal Soaring Weather Information#Cloud Bases]] will form, then at the **saturation adiabatic lapse rate**. As the first thermals of the day reach the CCL, they will form **cumulus humilis**. If diurnal heating continues and surface temperatures rise further, stronger thermals will form, and develop into **cumulus mediocris**. If atmospheric instability exists at higher altitudes, towering cumulus like **cumulus congestus**, and eventually **cumulonimbus** (thunderstorms!) will form. The moisture and stability of the atmosphere at a given time and place will determine which, if any, cumulus form. Paying attention to the lifecycles (time and development) of the clouds around you can make identifying a developing cumulus and the associated thermal significantly easier. ### Cumulus Features Several visual features of cumulus clouds offer insight as to what stage of development they are in: - crisp, well defined edges to the cloud indicate that it is still developing, while fuzzy edges indicate that the rising has stopped - any "churning" or "bubbling" at the cloud top indicates that it is still rising - a flat cloud base generally indicates development, while a convex cloud base indicates dissipation; a concave cloud base indicates exceptionally strong lift - darker cloud bases generally indicate taller clouds, and stronger lift - "wisps" or "tendrils" just below the cloud base indicate more moisture and buoyancy ![[cumulus features.png]] ## Non-Cloud Thermal Markers Without sufficient moisture, cumulus will not form, even though thermals are present. These "dry" or "blue" thermals can be found by a number of more subtle markers: - circling birds ("the professionals"), or another thermalling glider; be mindful of [[Collision Avoidance During Thermal Soaring]] - dust devils - haze domes, or any disturbances seen within visual obscurations at altitude - looking for the source of [[Heat Imbalances]] at the surface, and talking to local pilots about **house thermals** ![[haze domes Bermuda High SC.png]] \[haze domes seen at Bermuda High Soaring, Jefferson SC] ## Searching Once a pilot has identified the marker of a suspected thermal, they must locate the thermal itself. [[Anatomy of a Thermal#Wind Effects]] will almost always be present, so the pilot must account for the downwind drift of a thermal by estimating the effects of the wind at all altitudes the thermal ascends through. This generally means searching downwind of the source, and upwind of the cloud base or other high altitude marker.