Blue hole
An area without cumulus in an otherwise cumulus-filled sky, where thermals are weak or absent.
What it means
A large blue hole often points to more stable air or sink, though a lack of cumulus does not by itself prove there are no thermals. A blue hole is a bounded patch, whereas on a blue day thermals produce no cumulus anywhere.
Example in context
I didn't fancy crossing the blue hole, so I went round it under the clouds.
Sources and review
- FAA Glider Flying Handbook, Chapter 10 (Soaring Techniques) (opens in a new tab)
- Jakub Vrána — Paraglidingový slang: o počasí (opens in a new tab)
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