Navigating the Best Lift Underneath Cumulus Clouds

Cumulus clouds form when warm air rises, cools, and condenses into visible water droplets. Beneath these clouds, thermals create upward-moving air currents that we, as glider pilots, use to gain precious altitude. However, not all areas under a cumulus cloud will provide equal lift, and the challenge is determining where the strongest thermals are!

Factors in Identifying the Best Lift

1. Cloud Development and Shape

The first step in locating lift is analysing the development and shape of the cumulus cloud. A newly forming cumulus cloud usually offers the best lift, which signals an active thermal underneath. These clouds appear crisp, with well-defined edges and a cauliflower-like structure. In contrast, an older, decaying cloud has softer, less defined edges and may no longer indicate strong thermals as the rising air has already begun to dissipate.

So, always look for growing cumulus clouds with sharp features. These are more likely to have strong, sustained thermals beneath them.

2. The Upwind Side of the Cloud

Thermals are often influenced by wind direction. Air masses moving across the ground may affect where the thermal column rises beneath a cloud. In most cases, the strongest lift is found on the upwind side of the cumulus cloud. This is where the thermal initially forms and pushes upwards before the wind tilts the thermal column downwind.

To locate the upwind side, observe the cloud's movement in relation to the ground or look at wind indicators, such as farmers' lakes, smoke/dust, or surface winds. Position yourself on the upwind side of the cloud, where the thermal is most likely to be intact and rising strongly.

3. Cloud Streets and Alignments

Cumulus clouds often form in linear arrangements called "cloud streets," which are aligned with the wind direction... These streets indicate long, continuous thermals providing sustained lift over a greater distance. Using a dolphining technique, we can use cloud streets to cover large areas without losing altitude. The best lift within a cloud street is usually found under the newest and most defined cumulus clouds along the line, typically on the upwind edge of the street.  Flying along a convergence line? Usually, you’ll find the strongest lift under the darkest flattest area (up to 5km from —>) rather than right up against the cloud base that is seemingly much lower.

4. Ground Features

The terrain beneath the cloud also plays a critical role in identifying thermals. Certain ground features absorb more heat and are more likely to generate thermals. Dark fields, asphalt roads, dry lakes, and other areas that heat up faster than their surroundings create rising air currents, which may eventually lead to cumulus cloud formation. Observing the terrain under the cloud lets you anticipate where thermals are most likely to form.

Thermals tend to be stronger over areas of varied terrain or boundaries between different surface types, such as where a forest meets an open field.

Additional Considerations

1. Time of Day: Thermals are strongest in the late morning to early afternoon when the ground has had time to heat up but before the atmosphere becomes too unstable.

2. Cloud Spacing: Well-spaced cumulus clouds indicate individual thermals, while tightly clustered clouds may suggest weaker lift as thermals compete for air. A great rule of thumb is that the distance between the best thermals is 2 x the height of the cloud base.

To find the best lift under a cumulus cloud, start by analyzing the cloud's development, locating the upwind side, and noting cloud streets and ground features. Newly forming clouds with crisp edges offer the best thermals, and understanding wind direction helps pinpoint where the strongest lift will be. With practice, locating the strongest cores greatly helps optimize our flight, racing speeds, confidence, and enjoyment!

Safe circles, as always :)

Banner photo by Sean Franke

 Adam Woolley was born into the gliding world, being the 3rd generation in his family. Going solo at 15, his thirst for efficiency in soaring flight & quest for a world championship title to his name has never wavered. One big passion is sharing his experiences & joy with other glider pilots all around the world. Adam is an airline pilot in Japan on the B767 & spends his off time chasing summer around the globe. He has now won 7 national Championships & represented Australia at 5 WGC's & 1 EGC.