I've seen that same phenomenon happen around here. A thunderstorm will pass by, floating like a ship in the clouds. It rains like heck in the neighborhood next door but we get nary a drop.
In fact, for some reason, El Lago seems to be in something of a rain shadow. We do get lots of rain, but the big storms seem to like our neigbors to the north and south better.
Does it rain out there in the Great Sandy Desert during the moonsoon?