Basic VFR Weather Minimums (FAR 91.155)Class EUnder 10,000ft MSL:3 Statute Mile Visibility
Must maintain 500ft below, 1000 ft above, and 2000 ft horizontal distance from all clouds
At or Above 10,0005 Statute Mile Visibility
Must maintain 1000 ft below, 1000, ft above and 1 statute mile horizontal distance from all clouds.
Some Controlled airspaces must be clear of all clouds such as class B.
Class C and D require the above minimums.
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Basically if the weather does not meet these requirements ATC requires you to open an IFR flight plan, however you don't really need to contact ATC in the sim so its up to you to fly or not