Think back. What’s the most surprising thermal source you can remember? If you’ve had much experience it may take a while to decide. Each one has something to teach us. Some are ideal examples of basic concepts we all should understand, and others seem to defy those – until you look closer.
My most surprising? I’ve stumbled into more sweet freebies than I deserve, and far too many to count. For some the source was obscenely obvious, being so low at the time, and for others only one source was even possible. Yet often, especially in mountains, combinations of effects are what make the difference. So from a multitude of surprise thermal sources here’s a sampling in no precise order, of surprising kinds.
Least but not last, a concrete pad 30’ X 40’ (measured on GoogleEarth) in a huge open field with no other features except flatness. As we climbed away we sniffed elsewhere over that field, but always came back to the pad. Pretty sure that student would have written me off if it hadn’t worked.
A few miles from there one very small shack as deeply isolated offered equal benefit, though I suspect it was more thermal trigger than thermal source. That’s a distinction with a real difference we’ll get back to.
Looking for a sure thing? When farmers are cutting hay or corn in direct sunlight, you may as well bet on it! Or if they’re spreading liquified manure under full sun, same deal… almost. That can get smelly if thermals aren’t going very high, but contrary to what you’re thinking, there’s generally no brown cumulus. (Just for the heck of it though, imagine you have both to choose from. If you fail to climb in the first case, they just cleared a landing area for you. Fail in the second case… you’re on your own!)
Here’s one I can’t claim as my own discovery, but it merits inclusion for novelty alone. A former student not known for prevarication claims the lift rose from a freight train parked on a siding – and when the train eventually moved his thermal went with it… into the wind! Gotta love when that happens.
Now everyone knows that moisture inhibits thermal production, right? Well… Exposed water raises humidity at the surface, making the air there more buoyant, and a pond of just the right size can sometimes spawn weak thermals. Also, on cold New England days swamps may work when clear ponds don’t. Is that because of cooties in the mud and water? I say it’s the frogs. With either of these examples however, don’t expect a rocket ride to cloud base.
Then how ’bout a half-mile square field under intensive irrigation? Seriously. Local experts hypothesize that air above the field becomes so saturated and cool it amounts to a small hill over which desert winds must flow. Thermals triggered in this way may be softer than those from a real, solid hill, but lift there can be steady all day until they shut off those giant sprinklers.
And could you believe a flock of sheep high in the Rockies? True, they wear thick wool coats, but don’t forget they’re exhausting warm moisture from both ends almost constantly! Not much different from a feed lot or industrial armpit really, except the aesthetics.
Which brings us to my very first thermal… ever. It was April, gray and gusty, above a small-town racetrack. Wind pushed heat from raging stock cars against the grandstand, where a concentrated crowd added even more warmth while kicking the whole dusty bubble loose. Those factors and nothing else allowed us to orbit overhead at a constant height until we couldn’t take it anymore.
I remember thinking we had to be having more fun than those below us, until their fumes drove us away.