Trailing vortices have characteristics which, when known, will help a pilot visualize the wake location and thereby take avoidance precautions.  Vortex generation stars with rotation (lifting off of the nose wheel) and will be severe in that airspace immediately following the point of rotation.  Vortex generation ends when the nose wheel of a landing aircraft touches down.  Because of ground effect and wind, a vortex produced within about 200 feet AGL tends to be subject to lateral drift movements and may return to where it started.  Below 100 feet AGL, the vortices tend to separate laterally and break up more rapidly than vortex systems at higher altitude. The vortex sink rate and leveling off process result in little operational effect between an aircraft in level flight and other aircraft separated by 1000 feet vertically.   Pilot's should fly at or above a heavy jet's flight path, altering course as necessary to avoid the area behind and below the generating aircraft.  Vortices start to descend immediately after formation and descend at the rate of 400 to 500 feet per minute for large heavy aircraft and at a lesser rate for smaller aircraft, but in all cases, descending less than 1000 feet in total in 2 minutes.  Vortices spread out a at a speed of about 5 KT.  Therefore, a crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex.  Thus, a light wind of 3 to 7 KT could result in the upwind vortex remaining in the touchdown zone for a period of time or hasten the drift of the down wind vortex toward another runway.   Similarly, a tail wind condition can move the vortices of the preceding landing aircraft forward into the touchdown zone.  Since vortex cores can produce a roll rate of 80 degrees per second or twice the capabilities of some light aircraft and a downdraft of 1500 feet per minute which exceeds the rate of climb of many aircraft, the following precautions are recommended.  

Pilots should be particularly alert in calm or light wind conditions where the vortices could:
    A) remain in the touchdown area; 
    B) drift from aircraft operating on a nearby runway; 
    C) sink into takeoff or landing path from a crossing runway 
    D) sink into the traffic pattern from other runway operations  
    E) sink into the flight path of VFR flights at 500 feet AGL and below.