Flight Outside of Conservative Weather Parameters.
What it is.
Flying a paraglider with cumulus congestus, cumulus nimbus, mammatus, or virga in the same valley system.
Flying mountainous terrain with winds more than 12mph at peak level, more than 9 mph at the level of any ridges or spines you may be flying near.
Flying a paraglider anywhere with surface wind at or above 15mph.
Risk in the mountains caused by winds is increased when the winds are cross; particularly so when cross from the north.
Flying a paraglider in mid-day temps above 100 degrees Fahrenheit.
Flying a paraglider during times of extremely high pressure, pressures above 30.4 inches of mercury. A barometer reading of 30 inches (Hg) is considered normal. Strong high pressure could register as high as 30.70 inches, whereas low pressure associated with a hurricane can dip below 27.30.
With regard to wind in the mountains:
Mechanical turbulence and rotor downwind of obstacles start with winds at about 9 miles per hour. At 12 miles per hour that turbulence has the strength to collapse a paraglider. At 15 miles per hour, the collapses become difficult to block. At 18 miles per hour, even the very best among us will lose their wing.
Cross winds cause the strongest turbulence. The closer to 90-degree angle across slope, the greater the turbulence.
Cross winds create turbulence above the sunny aspects that most thermals rise through. As a result, thermals gain turbulence which they can carry over 1000 ft above the ground.
High pressure creates smaller, stronger, higher thermals that can collapse a paraglider.
Pilots new to mountain flying and all intermediate pilots should look for flying days with the following winds aloft maximums:
12mph at 12,000 ft.
10mph at 10,000 ft.
08mph at 8,000 ft.
Surface winds below 9mph
What it is not.
Flying a paraglider in calm air from a gently sloped launch to a large obstruction-free LZ is the most risk-free form of paraglider flight.
How to avoid it.
Begin your day early studying weather forecasts. Learn to read them and what they mean. Watch the wind, clouds and birds as you travel to and set up on launch. As you fly continually assess the wind strength and cloud development. Know that the cloud above you is likely similar to the other clouds you see, particularly with regard to height.
How to reduce consequences of bad weather.
Know how to get down quickly. If you see a weather risk you do not wish to accept, fly away from terrain & land. Find the greenest most obstruction-free landing area you can and land as far away from even the smallest obstacles as possible. Don't launch if you have doubts about wind strength, direction, strength of thermals or possibility of overdevelopment.
(Thanks to UHGPA for this weather parameter guide)