There are four types of restricted visibility: smoke, fog, falling snow, and blowing snow. Each type of restricted visibility has a different number of blasts.
Smoke: Three blasts in rapid succession followed by a pause of at least 60 seconds.
Fog: Five blasts in rapid succession followed by a pause of at least 60 seconds.
Falling Snow: Four blasts in rapid succession followed by a pause of at least 60 seconds.
Blowing Snow: Six blasts in rapid succession followed by a pause of at least 60 seconds