drizzle

According to NOAA, drizzle is fairly uniform fine precipitation with drop diameters less than 0.5 millimeters. The drops are very close together. Drizzle floats with air currents, like fog, but falls to the ground. Its intensity is determined by visibility:

Drizzle Intensity	Visibility
light	more than ½ statute mile
moderate	¼ to ½ mile
heavy	less than ¼ mile

NOAA.
Glossary: D's.
www.srh.noaa.gov/jetstream/append/glossary_d.htm
Retrieved 1 January 2010.