Thursday, February 22, 2007

Mackerel sky.

"Mackerel sky, mackerel sky - never long wet, never long dry. "

Is there any truth in this piece of folklore?

A mackerel sky is composed of patches of altocumulus cloud. It represents a layer of unstable and humid air which often follows a ridge of high pressure and precedes a warm front by about 400km. As warm fronts move about 50km/hr you can expect a change in the weather in about 8 hours. This was taken at 11am on our trip from Loch Sunart to Mull on 18/2/07. The wind picked up to force four from the SE by 12:00. By 14:00 the wind had increased to force 5 and it clouded over by 14:30. It was raining by 23:00.

On Saturday 17th February, when we were planning our trip, Scotland was under a ridge of high pressure and there was no wind. Sunday 18th dawned clear and still but the BBC forecast for Tobermory and Mull was for 17mph SE winds. The met office inshore forecast issued at 0600 UTC on Sunday 18 February 2007 for Mull of Kintyre to Ardnamurchan was:

Wind southeasterly 5 or 6, occasionally 7.
Precipitation: rain then showers.
Visibility: moderate or good.
Sea state: Moderate occasionally rough.

Although apparently sheltered, the Sound of Mull can be very rough especially in wind against tide conditions. LW Oban was at 12:35, 1 day before springs. Streams in the Sound of Mull change at HW and LW Oban. The flood flows to the NW and the ebb to the SE. When we crossed the Sound we had force 4 SE wind against the last hour of the ebb and it was rough in the middle. Although the wind was forecast to increase later, we enjoyed our stop at Tobermory as I knew that by that time the flood would have started and being with the wind, it would flatten the water. This is exactly what happened.

The white horses disappeared and the water flattened as the flood built up speed. We had a trouble free paddle back to the shelter of Loch Sunart.