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On the topic of weather photos...

Ian Fergusson | 11:36 UK time, Tuesday, 6 October 2009

A thank-you is due to Nigel Punchard of Midsomer Norton, Somerset, who sent me a wonderful photo he took above his home of Cirrus clouds - not taken in today's inclement conditions, I hasten to add!

"I call them curtain clouds, but you might be able to give me a better explanation," Nigel writes.

Virga falls from Cirrus clouds above Somerset (Photo: Nigel Punchard)Cirrus uncinus & Cirrocumulus with virga, above Somerset (Photo: Nigel Punchard)

His photo shows streamers - or 'curtains' as he describes them - dropping below the wispy high-altitude Cirrus (primarily Cirrus uncinus in this case, with some Cirrocumulus mixed-in).

These are actually falling ice crystals, never reaching the ground from such heights, but a genuine form of precipitation nonetheless. When rain, ice crystals or snow falls but evaporates before reaching the ground, it's a phenomenon called 'virga' or 'fallstreak'.

Sometimes, these falling ice crystals - if large enough - descend down into layers of cloud far below. In doing so, they provide the tiny particles, or nuclei, required to generate further precipitation falling in turn to ground level.

It's called the 'seeder-feeder' effect and often an important mechanism in the rainfall we experience across the British Isles.

Nigel's photo is a great example of virga - I'll surely use it in due course as a backdrop on BBC Points West weather bulletins. 

  cloud-of-day.jpgI'll often use cloud photos on my Points West weather bulletins, so do send them in by e-mail!

And talking of which, if you ever wondered how to submit photos for us to use (and we get asked this a lot), here's the basics:

  • Take them in landscape format only (not portrait)
  • Try to keep the subject of interest centrally and don't zoom tightly. This is because we have to crop the top and bottom of the photo to make it widescreen format (16:9) for TV - so keep the shot wider!
  • Don't add false colours, gaudy effects etc., in photo manipulation software such as Photoshop. If a photo appears unduly tampered with or contrived, we simply won't use it.
  • Send us a high-resolution version please, because we will re-scale it at our end. Small, grainy and pixelated photos taken on a mobile 'phone are of no use!
  • E-mail your photo to us at west.weather@bbc.co.uk and include details of the photographer's full name, exactly when and where the shot was taken, and please give us written confirmation that the image is yours, with permission for the BBC to use it on TV and internet.

I look forward to posting some of your photos here on the blog!



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