Definition
The prevailing horizontal visibility expected at an airport during a specified period, given in statute miles in a Terminal Aerodrome Forecast (TAF). Values of 6 statute miles or less are stated as a specific number (for example, 3SM); visibility greater than 6 statute miles is encoded as P6SM, meaning 'plus 6 statute miles.'
Plain English
How far the forecaster expects pilots will be able to see horizontally at the airport during the time period covered by the forecast.
Context Anchor
Seen in Terminal Aerodrome Forecasts when reading the expected weather at an airport before a flight.
Derivation
“Forecast” means to estimate beforehand. “Visibility” comes from a word meaning “able to be seen.” Together, the term points to a predicted seeing distance, not a measurement taken right now.
Why Pilots Care
Sets the expected conditions for deciding whether visual flight rules remain usable or instrument procedures become necessary for arrival and landing.
Grounding Statement
If a TAF shows lower forecast visibility near your arrival time, expect the airport area to be harder to see as you get close.
Intuition Check
Do not treat forecast visibility as a guarantee of what you will see when you arrive. It is the expected prevailing visibility for that time period, and the actual visibility can be better or worse.
Example Sentence 1
The TAF showed a forecast visibility of 2SM in mist for the early morning, so the pilot delayed departure until conditions were expected to improve.
Example Sentence 2
When forecast visibility falls to 2SM, the pilot begins reviewing the instrument approach plates for the destination airport.