Found this - Creating ridge lift in the mission builder of FSX:
http://carrier.csi.cam.ac.uk/forster.../dev/lift.html
"FSX has great tools for the creation of ridge lift in the mission editor, so you can design ridgelift boxes working in a very realistic way. Here's a screenshot within the Mission Editor using a development visualisation model: "
"A RidgeLift object is used to simulate the effect of a hill slope on the wind."
From that link:
"Here's a list of rules to make your thermals and ridge lift move realistic:
Thermals:
1. A lift strength of 5-6 knots (2-3m/s)would be a good day in most of Europe or the eastern USA.
2. Make them the kind of diameter you can circle in, but not much larger. I'll try and quantify this...
3. Thermals should NOT be designed to go above the cloudbase. Normal cross-country flights involve climbs to cloudbase and no further. Typical cloudbase in Europe and NE USA is 6000 feet.
4. Plant more thermals but make many of them weaker. Real gliding involves sampling and rejecting many more thermals.
Ridge lift:
1. Wind of 16-24 knots is good for ridge lift
2. Lift at ridgetop is typically 5 knots, so you can cruise at 100 knots without losing height.
3. Lift extends to 1000-2000 feet above the ridge but reduces in strength. At 2000 feet above the ridge you might be able to maintain height at best glide speed."