Day VMC depends on your position under and over "S" surface, FL 100, and the controlled/uncontrolled status of the airspace you're in.
Visibility must be at least 8km over FL100, 5km under FL100. You must be able to fly no closer than 1500m from clouds, horizontally, and 300 meters vertically.
If visibility is not as good as that, you must request a "special VFR" clearance allowing you to fly in these airspace with a low visibility.
Over "S surface", VMC are identical to VMC in controlled airspace. Impossible, however, to get a special VFR clearance in uncontrolled airspace. sadly enough, it means that if visibility is poorer than 5km, in uncontrolled airspace you have no choice but fly near the ground, which is dangerous.
Under the "S" surface, visibility must be at least 1500m (800m for helicopters) or the distance you will fly in 30 seconds, whichever the longest. You just have to fly out of clouds, with no minimum distance from them.
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