High Humidity

[Michael Lerch]

This pic was one of many taken on the way home from work. Tempe Az is a town between Phoenix and Mesa. A few miles wide and deep. While still in Mesa I noticed strange cloud movement and pileus only occurring in the clouds over the general Tempe area. And so it was for about an hour. This shot is of a Pileus. Notice it is not on top as pileus usually is and even the clouds are not all that soaring to compress the atmosphere above them. It was very Humid in the Tempe area while taking these pics.The cell only existed over Tempe. The lesser clouds over Mesa and Phoenix did not produce Pileus nor velum. The saturated cell appeared to be rolling back from the hills, the north east. A very local event providing an outburst of veil.

[Gavin Pretor-Pinney]

That’s a great example of a pileus us cloud, Michael. Well spotted!

For those who don’t know, the name comes from the Latin for a ‘hat’. It’s a smooth cap of cloud that forms momentarily over a developing convection cloud (usually a Cumulus congestus) as the air rising from below lifts an airstream passing overhead. As this airstream is lifted, it can cool enough for some of its moisture to form into droplets which we see as a smooth patch of cloud. Inevitably, the building Cumulus cloud carries on growing higher and subsumes the pileus above.

[Howard Brown]

Beautiful, intriguing picture, MikeL, many thanks. One wonders about the dimensions of the airstream e.g. a continuous gradient or a band or what. Perhaps Mike The Soarer would know.

[Michael Lerch]

Thanks Gentlemen! Hygge, in my minds eye the high humidity area seemed a blob that strangely appeared to come from the east north east. As I have said, rolled back from the hills since most weather comes up from the south west towards the north east. A band? Seemed to me a gradient, an invisible cell of saturated atmosphere.

A few more pics from the event are below. Velum is captured in the black and white shots. The color shot is the last shot I took during the event. As you can see, the wind ,again, has begun tearing things apart,,but notice,,how the pileus streams over to start forming its own velum cloud!

[Howard Brown]

TOPNOTCH CLOUDSPOTTER

MikeL, this topic with its initial picture, GP-P approval, then the synoptic situation, makes you Top Notch in my humble opinion.

Thank you.

[Michael Lerch]

Thank you Hygge, I have a good time , well actually I lose track of time, when I photograph the clouds. I experience a freedom that does me good.

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