What is the windspeed where an average sized person cannot walk or stand?
As with terminal velocity, the speed varies depending on the cross section the person is applying to this gust of wind. If the gust were coming straight from under the person’s feet and the feet and arms were pressed in, you might need a 200 mph gust. The normal free-fall position (belly down) has a terminal velocity of about 122 mph, according to sky divers.
There are a ton of other factors that will have to be taken into consideration. You say an avg sized person, but what weight, height are they, are they on level ground, are they leaning into it trying to balance etc. Also friction caused by there clothes can affect them. With that said, more area equals more friction equals less wind speed to knock someone over. Some people have been knocked over by a 50-60 mph gust. But in general, if you were prepared for the gust, probably 100-120mph. But a ton of things to consider.
