Definition
A category of weather conditions in which flight under visual flight rules is still legal, but the ceiling and visibility are reduced enough to make visual navigation noticeably more difficult. MVFR is defined as a ceiling between 1,000 and 3,000 feet AGL and/or visibility between 3 and 5 statute miles inclusive.
Plain English
Weather that is still good enough to fly by looking outside, but only just. The clouds are lower and the visibility is shorter than normal, so you have to be more careful.
Context Anchor
You will see MVFR in airport weather reports, forecasts, preflight planning tools, and weather briefings.
Derivation
‘Marginal’ comes from the Latin margo, meaning ‘edge’ or ‘border.’ MVFR weather sits on the edge between comfortable visual flying and conditions that require flying by instruments.
Why Pilots Care
Pilots use MVFR reports to decide whether visual flight remains practical or whether instrument procedures and alternate planning are required for safety.
Grounding Statement
In MVFR, you may be able to fly by looking outside, but the view and cloud clearance are limited enough that small changes in weather can matter quickly.
Intuition Check
MVFR does not mean “good VFR” or “automatically safe for visual flying.” It means the weather is marginal: still usable in some cases, but close enough to lower limits that it deserves extra caution.
Example Sentence 1
The forecast showed MVFR conditions along the route, so the pilot reviewed alternates before departing.
Example Sentence 2
The briefing showed MVFR along the route due to a 2,500-foot ceiling and four-mile visibility, prompting extra fuel reserves.