Clouds as Signposts (continued)

         When the sky is filled with a variety of cloud shapes, we have the best opportunity to compare what we think they signify to what they really mean.   The tops of clouds are usually obvious.   Bulging shapes with distinct surfaces generally mean stronger convective activity, and tattered edges are a sign of decay.   Great vertical depth indicates strong lift below (and within) a cloud, and suggests higher humidity, while any tendency to lean is a sign of wind direction and strength.   More useful on a moment-by-moment basis, however, is a subtler kind of information coming from the parts of clouds nearest to us and easiest to examine:  their bases.     At first, all beginners hear that the base of a good cumulus is flat, but there are degrees of flatness, and important exceptions to this rule.   Another descriptive detail is something vague about the bases of active cumuli being ‘concave’.   Sometimes a powerful thermal will build a cloud whose base is very smooth, but actually in the shape of a broad, flat cone, with the strongest lift rising into the highest part of the cone.   One of the many ironies of soaring is that, like seemingly inevitable unwanted thermals in the landing pattern, we often encounter our strongest lift of the day at cloud base, exactly where we need it least.   When you can see straight down but the horizon is obscured by surrounding parts of the cloud base below you, you’re already too high.   The lift there may be so strong that it’s no longer possible to avoid rising into...     Sometimes the bases of cumuli occur at different heights, and this itself can help you decide which one to approach.   During the early half of a good thermal day the average cloud base may steadily rise, perhaps a thousand feet per hour.   If the day is still gaining strength, you can expect stronger lift from newer thermals under higher cloud bases.   Also, regardless of the time of day or any other variable, higher bases imply a greater volume of rising air, and therefore more lift.   Even without a better climb rate, higher bases allow you to soar further above the ground and therefore glide farther before needing to climb again.   So, in selecting your next cloud, it is probably best to choose the one with the highest base in the direction you wish to go.