Lenticular clouds

I just heard on the radio that weather conditions in Sydney today are such that there’s a high probability of a lenticular cloud forming over the city late this afternoon, as the day cools. If it does, it will likely run from northwest to southeast, and should look fabulous from the east with the sun behind it as it sets.

Image Credit Rob Alexander: click image for full size

Lenticular clouds only form in conditions where the air forms pressure waves that lead to the cloud clumping and layering with clear air separating it from other clouds.

Normally, air moves much more horizontally than it does vertically. Sometimes, however, such as when wind comes off of a mountain or a hill, relatively strong vertical oscillations take place as the air stabilizes. The dry air at the top of an oscillation may be quite stratified in moisture content, and hence forms clouds at each layer where the air saturates with moisture. The result can be a lenticular cloud with a strongly layered appearance. [APOD]

Lenticular clouds also have a fabulous long technical name that is going to be the core of the next drinking game I play: altocumulus standing lenticularis. They are also an object of particular delight to glider pilots, as the same combination of winds and updrafts that allows them to form also provides a rapid lift and a long flight in a glider. Indeed, it was a glider pilot who rang the radio station to talk about the likelihood of a lenticular cloud forming today: he described lenticular clouds as like a cigar sliced in half, with the flat side underneath and the rounded side on top. I’ve read more elegant descriptions, but that’s a very vivid one. They have been mistaken for flying saucers as well when they are more rounded than cigar shaped.

mount erebus
Image Credit US Coast Guard via Splendid Pictures (Warning: Serious Procrastination Alert)

With Sydney’s low hills of the Blue Mountains escarpment being the catalyst for lenticular cloud stacking, they are unfortunately not high enough to produce the truly spectacular results in the pictures linked to above. But we do get formations like these below:
lennie near coastedge of lennie overhead
Image Credit: Oz Thunder

I hadn’t realised they were the undersides of lenticular clouds, but I’ve quite often seen leading edges like the second picture moving overhead. Cool. There’s lots more altocumulus clouds at OzThunder, and many more cloud types too.

Also mentioned on the radio was the term “Mackerel sky” which apparently involves lots of small spot clouds. I have to go pick up the kids soon, so I haven’t googled that one.

Categories: arts & entertainment, Science

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11 replies

  1. Cool. Hmm – must get out of the lab before it’s dark, today.

  2. Ah, lots of pictures of mackerel skies [here]. It’s another variation of altocumulus, but this time the pressure doesn’t oscillate in the same way that forms lenticular stacks, and we end up seeing scattered clouds clumping in a fashion similiar to the scales of a mackerel.
    Indeed, according to WeatherOnline there are two variations – ripples of altocumulus look like the scales of a King Mackerel, while patches of cirrocumulus look like the scales of a Spanish Mackerel. There’s some nice detailing of the weather facts behind the weather lore there as well (Mackerel sky, mackerel sky – never long wet, never long dry and Mare’s tails and mackerel scales make lofty ships take in their sails).
    So if we don’t get our lenticular clouds we may well get a mackerel sky, and if we do watch out for the rain!

  3. Oh, cool. Shame I’ll be on the wrong side of the country.
    We did get a fantastic look at the comet, though.
    While we’re on interesting and amusing clouds, a friend of mine took this photo a while back. (Possibly very, very marginally NSFW.)

  4. Well I understand why her photo’s had over 12,000 views.

  5. Back from sunset viewing – we didn’t see lenticular stacking (although there were a couple of suspect elongated clumps disintegrating by the time I got to the hill). However, there were altocumulus ribbons galore and plenty of promising shots, enhanced by the full moon rising behind us as the sunset faded to pink. One of the best sunsets I’ve seen there, plus there were all the dogs at Sydney Park coming to say hello. Nice way to spend the early evening.
    I’ll try and get the best up on to Flickr tomorrow.

  6. Last Saturday was the best day in a long time for cloud watching, at least four different kinds, at different altitudes. So brilliant that I tripped on the footpath, jarred one tin knee, landed on the other foot and jarred the other tin knee. I limped home looking at concrete.

  7. Ow!
    JahTeh, I was trying to remember who’d blogged about lenticular clouds last year – was it you?

  8. Thanks. Loved this. I’ve never heard of a lenticular cloud before.

  9. Yes, twas I who blogged the “Lennies” including that brilliant one that looked like the starship “Enterprise”.

  10. Sunset photos blogged! [link]


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