Definition
An obscuration to visibility caused by extremely small, dry particles suspended in the atmosphere — such as dust, smoke residue, salt, or pollutants — that individually are invisible but collectively reduce horizontal visibility and give the air a milky or opalescent appearance. In a METAR, HZ is reported in the present weather group when these particles reduce visibility to 6 statute miles or less.
Plain English
Tiny dry particles in the air that you can't see one by one, but together they make the air look hazy and cut down how far you can see.
Context Anchor
Pilots see HZ in aviation weather reports, especially in the present-weather section of a METAR when visibility is reduced by haze.
Derivation
From an older English word meaning 'misty' or 'foggy.' The aviation use keeps the everyday sense — a soft, milky reduction in visibility — but ties it specifically to dry particles rather than water droplets.
Why Pilots Care
Haze reduces visibility enough to affect VFR minimums, increase workload during approach, and raise the chance of spatial disorientation or runway incursions.
Grounding Statement
On a hazy day, the sky may look bright, but distant objects can fade or disappear because the air itself is limiting what you can see.
Intuition Check
Haze does not simply mean “a little cloudy” or “bad weather.” In aviation weather, HZ points to tiny dry particles in the air that reduce visibility.
Example Sentence 1
The METAR reported HZ with visibility of 4 statute miles, so the pilot planned for reduced slant-range visibility on the visual approach.
Example Sentence 2
During the approach briefing the crew noted HZ and increased the decision altitude to account for reduced forward visibility.