Do you know what a Morning Glory is?  I have experienced two of them in my ballooning years.  The first one I tried to land and hit the ground doing 42mph.  I have no idea how far we drug.  When we hit I actually caught one of my passengers as they were flying over me on the way out of the basket!

Morning Glory's are super rare but here is one of the theorys of how they happen.  Over night the ground radiates the heat and moisture from the previous days convective lifting.  Some areas have more heat to give than others.  Occasionally the atmosphere is heavy with moisture.  This radiant heat holds that moisture up over night.  The next morning when the sun comes up it begins to heat the earth and cuts off the heat coming from the ground.  This acts like a trap door dropping the moisture rich air aloft to the surface of the earth.  The effect is just like doping a brick into a lake.  Rings of cloud form and radiate out at very high speed. 

You will see a wall of cloud racing at you.  GO UP!  Ride it out!  Things will eventually calm down.  Then be real careful when landing because you will have very poor visibility.  Some times only a quarter mile.  Seriously not fun.  I have had two 40+ MPH landings in my 50 years. Fortunately I am here to talk about it.