Liz and I drove from Martinborough to Palmerston North today and enjoyed an unusual cloud formation that covered a large part of the sky in northern Wairarapa. These photos were taken just at the beginning of the Pahiatua Track, an alternative route to Manawatu over the Tararua Ranges.
[Later: this post excited a bit of comment – see below. It seems the clouds were a rare variety known as Undulatus Asperatus.]
Click to enlarge images.
Martinborough Musings 
Well, my friend, it seems you’ve discovered a new type of cloud. These look very similar to the ‘Asperatus’ clouds over on National Geographic’s post ‘New Cloud Type Discovered?’
Asperatus clouds are listed in National Geographic’s
‘Top Ten Discoveries of 2009: Nat Geo News’s Most Viewed’
http://news.nationalgeographic.com/news/2009/12/091202-top-ten-discoveries-2009-year-science-news.html
Similar for sure. The Wairarapa version is a bit smoother – more pillow-like than wave-like.
Yes, I think that is an example of “Undulatus Asperatus.” The Latin roughly translates to “turbulent undulation.” It is not a common cloud and was in the news in the middle of 2009 as a “newly discovered”. It has been around since water vapour was an important constituent of the atmosphere. The “new” aspect is that it has only recently been identified and named.
There are already some references to other sites in earlier replies – here is another one… http://www.meteorologynews.com/2009/06/06/new-cloud-type-discovered-undulus-asperatus/
Ross is a meteorologist at the NZ Met Service. The URL he gives for other examples of this cloud formation shows examples that are closer to those I photographed, than the National Geographic examples.
Thanks, John. I gave that link for just that reason. I have seen the same cloud forms several times in the last few years over Upper Hutt where I live… just fairly gentle undulations, like the ones you saw. In all cases, the wind was from the west or northwest, and rain was expected. Contrary to what is commonly written about this, there was no thunderstorm activity.
I have not seen it in a southerly situation. I suspect that a necessary condition is a stable atmosphere – the observed waves and undulations support that idea. Southerlies in Wellington are generally in unstable conditions, or there is not a continuous slab of cloud to reveal the form.
The formation doesn’t seem to last very long – an hour or two. I have not seen any comments anywhere about how long this spectacle lasts. All the cloud forms have a typical time scale, and as far as I can tell from what I have seen, this particular cloud formation is in the hour-or-two time scale.
Conditions on the day were what Ross described as typical for this cloud formation: north-west winds with forecast rain. It eventuated too – when we came back later that day, the weather was dramatic: high wind and torrential rain in the northern Wairarapa, starting between Pahiatua and Eketahuna, and extending 10 kilometres or so south of Eketahuna. There was no thunderstorm activity.
Hi John
Never seen clouds like this in the UK! Wow, hope you’ll save some for when I eventually get to visit you.
Mo