Cloud Shadows

[in the vale]

I have just been out walking the dog and was admiring the very clear retreating back edge of the front that has now passed over North Wales. It was clear from N to S as far as the eye could see. Then about 10-15 minutes after the sun went down it became a glorious orange colour, and it was then that I noticed a big shadow on the cloud that slowly moved south over time. The cloud was still there, but obviously something was causing this huge shadow. We have quite a few hilly areas between me and the setting sun, but the obvious candidate was the Snowdonia range - 30 miles as the crow flies. Is this likely? If so, it was a pretty impressive shadow created 30 miles away. I am not sure of the height of the clouds, but does this seem possible? Thoughts?

[knocker]

I have just been out walking the dog and was admiring the very clear retreating back edge of the front that has now passed over North Wales. It was clear from N to S as far as the eye could see. Then about 10-15 minutes after the sun went down it became a glorious orange colour, and it was then that I noticed a big shadow on the cloud that slowly moved south over time. The cloud was still there, but obviously something was causing this huge shadow. We have quite a few hilly areas between me and the setting sun, but the obvious candidate was the Snowdonia range - 30 miles as the crow flies. Is this likely? If so, it was a pretty impressive shadow created 30 miles away. I am not sure of the height of the clouds, but does this seem possible? Thoughts?

Where were you; possibly between Denbigh and Ruthin?

[in the vale]

Where were you; possibly between Denbigh and Ruthin?

Basically, yes. Slightly nearer to Ruthin than Denbigh.

[knocker]

I have just been out walking the dog and was admiring the very clear retreating back edge of the front that has now passed over North Wales. It was clear from N to S as far as the eye could see. Then about 10-15 minutes after the sun went down it became a glorious orange colour, and it was then that I noticed a big shadow on the cloud that slowly moved south over time. The cloud was still there, but obviously something was causing this huge shadow. We have quite a few hilly areas between me and the setting sun, but the obvious candidate was the Snowdonia range - 30 miles as the crow flies. Is this likely? If so, it was a pretty impressive shadow created 30 miles away. I am not sure of the height of the clouds, but does this seem possible? Thoughts?

My thoughts for what they are worth. Correct me if I make any wrong assumptions. At just before 1900 we take a straight line from the shadow to the setting sun (it may have just set where you are) which should be almost due west to just south of Caernarfon. The line should pass through Snowdon. If we take a point, say, halway up Snowdon, the sun will be slightly later setting there, than where you are. I.m assuming you aren't walking the dog on the highest point in the area. To cast the shadow the sun could not have set on Snowdon. Also of course there must be visible line of sight from the sun to Snowdon and I'm not familiar with the terrain. I suspect the cloud for this to apply would have to be quite high. The movement of the shadow I don't think is a problem as the sun doesn't set in a straight line but in an arc so if at this point it was moving slowly north the shadow would move south. You didn't mention how long the event lasted; I wouldn't have thought very long. Well is this the cause of the shadow? With Sherlock Holmes in the back of my mind, I can't at the moment think of an alternative. Which of course doesn't mean there isn't one. The only time I have seen shadows on clouds are from an aircraft but that is quite straight forward.

[in the vale]

Thanks for that WeatherShip - I didn't expect anyone to be so thorough! I worked out the same conclusion from the trajectories on a map. The event only lasted a few minutes, as the shadow was moving quite quickly. I was walking at just above MSL (6ft?). The height of the cloud is an unknown, but it looked quite high judged against the Clwydians below it. I took a couple of photos on my phone - I will try and upload them when I get a few minutes.  

[in the vale]

Thanks for that WeatherShip - I didn't expect anyone to be so thorough! I worked out the same conclusion from the trajectories on a map. The event only lasted a few minutes, as the shadow was moving quite quickly. I was walking at just above MSL (6ft?). The height of the cloud is an unknown, but it looked quite high judged against the Clwydians below it. I took a couple of photos on my phone - I will try and upload them when I get a few minutes.  

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Second photo is the back edge to the north of the shadow, the first is a pic of the shadow (photoshopped slightly so the shadow is clearer) 

Edited September 30, 2010 by in the vale

[knocker]

From the photos, the cloud appears to be Cirrus which would put it probably between 20, 000-30,000'. Assume 25, 000' and calculate whether that fits from your map and diagram.

Edited September 30, 2010 by weather ship

[in the vale]

Gosh - that involves trigonometry! I'll have to get some string and a scale model sorted then....