UVV stands for Upward Vertical Velocity. There are many lifting mechanisms that contribute to rising air. Sinking air mechanisms, call DVV (Downward Vertical Velocity), are also significant since they can reduce or cancel lifting mechanisms. The net impact of UVV and DVV over a region determines whether the air will rise or sink at that location. UVV and DVV motion is the result of dynamic lifting or sinking and does not result from instability. The motion of UVV and DVV is much slower than instability release or downdraft motions in a storm but with persistence and enough lift the air can rise or sink a significant amount over hours of time. A forecaster will examine all the potential UVV and DVV mechanisms over the forecast region. The region where the mechanisms coming together result in the greatest lift is a potential burst point for convection. The three critical ingredients for thunderstorms are moisture, lift and instability. A high UVV value indicates lifting will be a positive aid in potential thunderstorm development. The 700-mb UVV panel shows the net result of UVV or DVV for each location over an area. This can be used as a quick guide to see where the greatest UVV is coming together. This will often be a circular or linear region of UVV on the model panel. The location that has the highest UVV can be the burst point for convective storms when adequate moisture and instability are in place also. The link below goes over various UVV mechanisms and how they influence a precipitation forecast. Other factors that go into a precipitation forecast are explained also: http://www.theweatherprediction.com/precipfx/ |