Definition
An ATC authorization issued to a Special VFR aircraft, requesting it to climb to VFR conditions on top of a cloud layer. The clearance contains the appropriate Special VFR conditions, and is issued only when there is reasonable assurance that the pilot can reach VFR-on-top conditions within the airspace authorized for Special VFR operations.
Plain English
When you're flying under Special VFR (a clearance that lets you operate in weather worse than normal VFR limits inside controlled airspace near an airport), ATC can tell you to climb up through the clouds until you break out into clear air on top. They'll only do this if they're confident you can actually get above the clouds while still inside the area where Special VFR is allowed.
Context Anchor
You may see this in controller-pilot communications when a pilot needs to climb out of an area with reduced visibility to reach better visual conditions above.
Why Pilots Care
Lets a pilot legally leave the IFR system once in visual conditions without needing a full VFR clearance or further vectoring.
Intuition Check
Do not read this as permission to climb through clouds. It means ATC has authorized the climb toward VFR conditions, while the pilot remains clear of clouds.
Example Sentence 1
Tower instructed the pilot to climb to VFR on top, and once above the broken layer he reported clear of clouds and continued on course.
Example Sentence 2
Once cleared to climb to VFR the pilot maintained the assigned heading until breaking out on top.