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Gin-clear Autumnal skies...

Ian Fergusson | 14:41 UK time, Monday, 12 October 2009

Wow, what amazing visibility greeted us this morning! Not a cloud in the sky here above Bristol, as high pressure now becomes dominant for quite a number of days ahead.

An Airbus A320 streams a contrail of man-made Cirrocumulus cloud (Photo: Barnaby Perkins)After finishing our local radio & TV forecasting this morning, I stepped-out into glorious autumn sunshine streaming across the courtyard here at the 91Èȱ¬ in Clifton. Far above, three airliners were completing their transatlantic journeys, presumably heading across to continental destinations. I was struck by how none of them left any - the ribbon of cirrus cloud that you often see streaming out behind the exhausts of high-altitude jets.

A sky of chaotic contrails - their longevity signalling the likely arrival of inclement weather (Photo:Laurence Coss)These contrails can be a , because they give an indication of the amount of moisture and instability existing high in the atmosphere.

If they are seen to persist for a long time, or get wider and more conspicuous, it suggests unstable atmopsheric conditions prevail high aloft - and typically, it's a precursor to the weather deteriorating.

Conversely - much like today - if the contrails are entirely absent or seen to quickly fade, it's a reasonable bet that fair weather is on the cards - at least for a while.

And indeed high pressure will dominate our weather now for a number of days ahead, albeit I'm expecting rather cloudier conditions across the West Country by midweek onwards.

But for now, if my view of these airliners is so crystal-clear from down here, imagine what a spectacular vista they must be seeing today from up there at 35,000 ft. Quite probably a view across all of southern England, pretty much coast to coast, I'd imagine!

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