Interpreting the jetstream forecast

[great_bear]

How far "away" from the UK on the map does the jetstream have to be in order not to spoil the views?

e.g. If the jetstream forecast shows it brushing the edge of the West Country coastline, then from London would I expect:

a) No interferance at all

Interference 45 degrees altitude and downwards on the west

c) Interferance nearly all the way to the Zenith downwards on the west

?

[great_bear]

Surely someone must know this?

[FraserClarke]

I don't know the precise answer I'm afraid... but you can do a few calcs.. the jet stream is at ~10km height, so for it to affect you at 45 degrees, it would need to be ~10km distant (along the ground)... so, unless it's right over you, it's probably not a strong effect.

Of course, the 'edge' of the jet stream is probably a rather fuzzy thing. Having said that though, I have certainly seen instances on big telescopes where you get a very significant change in seeing from one part of the sky to the other, which suggests there is a rather sharp edge at least some of the time...

[great_bear]

I don't know the precise answer I'm afraid... but you can do a few calcs.. the jet stream is at ~10km height, so for it to affect you at 45 degrees, it would need to be ~10km distant (along the ground)... so, unless it's right over you, it's probably not a strong effect.

Erm... That doesn't work out

In other words, for it to be as GOOD as 45 degrees, it would have to be 10km away. Any less and it makes even MORE of an effect, right?

It seems to me then, that unless it's north of your location, it's not good news...

[FraserClarke]

Yeah, I didn't write it very clearly

I meant that being within 10km was basically right over you (given you're talking about distances of a hundred km or more on maps typically).

[great_bear]

Sorry - I got confused - your original statement:

unless it's right over you, it's probably not a strong effect.

Is perfectly correct and reasonable of course, given the scale of the jetsteam forecast map.

For some reason I'd got it into my head that 10km was 10,000 miles(!) I perhaps wouldn't have made the mistake if it were written longhand as "kilometres" but I have a baby and don't get much sleep these days!!

[great_bear]

Just realised I've got this the wrong way around and was right the FIRST time in the thread above! The LOWER the jet stream in the sky, the more dramatic the effect would be, and - given the vast distances to the moon etc., and 10km (the height of the jet stream) being not a very great distance at all, it means the angle has LESS of an effect, not more.

Therefore, if the jet stream forecast shows it being over you to any degree, then that's it - you've kind of had it in terms of "seeing"

I'm sure someone will correct me if I'm wrong again