Confused about current visibility

[redneon]

So tonight should be the catalyst for a great viewing night. Indeed, the visibility reported here seems to agree: http://www.wunderground.com/global/Region/i_UK/2xVisibility.html. However, I've just been outside and I can't see a thing because of the amount of fog or freezing fog or whatever it is that I can see clogging up the air (you can see it particularly well around lamp posts).

I have two questions, really. Firstly, what is it? Is it fog? This seems like an incredibly basic question but if I don't ask I'll never find out Secondly, how can websites like the above report such a visibility under these conditions?

It seems to have been the same over the past couple of nights. What seems to happen is that, over the course of the next few hours, the fog settles and we're left with a beautiful night for viewing. But by that time it's 11pm and onwards and I'm up for work early in the morning.

[Astro Imp]

Well it's clearish here but a lot of dampness in the air, the dew is absolutely horrendous. I spent a couple of hours out but nothing was very clear. On top of that the moon was washing everything out and now the clouds are sweeping in.

I know this doesn't really answers your questions but I suspect that what you are seeing is mist, as for what the website reports needs to be taken with a (large) pinch of salt.

[Alien 13]

I just let the cat out and all i could see was a very hazy moon lots of high level fog.

[Marki]

Clearish here in York, but the air seems very wet and dewey, so the moon is washing stuff out a fair bit. Hoping it'll ease off before it clouds over, or before I have to quit for the night (early start in the morning).

[ronin]

It is a mist, fog has criteria concerning how far you can see - something like if visibility is less the 1Km then it is fog- that appears to be for aircraft, the Met Office suggest less then 200m for motorists/pedestrians.

Presume that as the air cools water vapour condenses out to form a light mist. May be formed by the interface of 2 layers higher up. So clear at ground level looking horizontally but a condensation layer to peer through if looking up.

What you are seeing may well fit the weather definition of "clear", also "clear tonight" may not mean clear at 21:00, maybe clear from 00:00 to 8:00 just not when you want it.

It seems to be getting thinner and thinner, by midnight should be good, also freezing cold by midnight, it ain't exactly warm at present.

[Moonshane]

last night my forecast was clear from 2-3am and Sat24.com also looked good. despite this and the forecast remaining unchanged I was covered with a thick blanket of mist / fog from 2-5am. Very frustrating. the weather is always going to be an issue in the UK though.

[Marki]

Cloudy now. Really get the frustration thing, Moonshane!

[NGC 1502]

Sometimes the forecast says 'clear' but is not good for our purposes.    If a few stars can be seen through the murk, then It's 'clear' as far as the general population is concerned.

But sometimes a very slightly misty night can have steady 'seeing', can be good for planetary detail then, but useless for deep sky.

It's a case of making the most of the conditions, we can't change it, but we can adapt to what we choose to observe.

Regards, Ed.