What does "visibility" mean on weather forecasts?
I was looking at what the weather will be tomorrow on the bbc weather site and underneath wind speed and all that it said "Visibility: Very poor". What does this mean?
- Michel VerheugheLv 71 decade agoBest Answer
For aviators, there are two kind of visibilities: vertical and horizontal. Together, they form the cone of visibility needed to be allowed to land on "visual flight reference" (VFR) flight.
For anybody else, the visibility is an estimation of the distance at which an object can horizontally be seen clearly.
Visibility is given in different units; nautical miles, for seafarers, miles or meter and feet for aviators and whatever is the unit of distance in the country, for anyone else: Miles or kilometers.
There isn't a definition of poor or very poor visibility in terms of distances. For information, European aviators receive a visibility only to ten kilometer. Anything above that is considered as excellent and doesn't need to be detailed.
Usually, airspaces are limited to visual flights to five or four kilometers visibility. In some cases (Special VFR) when remaining in sight of the airfield, it can be down to three kilometers. Anything under that need instrument flight reference (IFR) certification for both the aircraft and the airfled.
I would say then that "very poor" visibility is perhaps anything below three kilometers.
That happens when the relative humidity is very high, perhaps 100 percent and haze and perhaps patches of fog are lurking around. It happens usually in an inversion, i.e. when the air is warmer aloft than near the ground. And that happens usually in a high pressure and more often in the early morning.
- RosemarieLv 44 years ago
It means a rainfall rate of less than 2mm an hour. Moderate rain is 2-6mm an hour, heavy rain is more than 6mm an hour. An inch of rain is 25.4mm which, if it fell in an hour, would be very heavy rain.
- AdelaideLv 43 years ago
I'm interested in this as well
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- marilouLv 43 years ago
Wow, thanks! Exactly what I was looking for. I looked for the answers on the internet but I couldn't find them.