Naked Science Forum
General Science => Question of the Week => Topic started by: jamest on 13/06/2025 15:09:27
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When I'm cycling around the Suffolk countryside, I regularly notice that the clouds aren't moving in the same direction that the wind is blowing me. Sometimes they're moving in the opposite direction, other times across the wind I'm feeling and only occasionally in the same direction. Does this mean that high and low pressure areas are in different places depending on altitude? Or is something else going on here?
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Yes. Wind direction and speed does vary with altitude. This is why pilots, when making a flight plan, need to get a winds aloft forecast. https://www.usairnet.com/cgi-bin/Winds/Aloft.cgi?icao=PDX&hr=06
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Yes, there are all sorts of things happening at once.
Near the coast, at low level, you may have an onshore wind during the day as the land heats up quicker than the sea, which turns into an offshore wind in the evening. If the prevailing upper wind in westerly (normal for the British Isles) and you are near the east coast, the daytime sea breeze may be easterly so moving opposite to the high cloud
At high altitudes there is a fairly constant westerly "jet stream" that occasionally wiggles between northwest and southwest, and this modifies everything below it.
Weather in the British Isles is mostly dominated by low pressure areas drifting across the Atlantic. The wind blows anticlockwise around the center, which usually passes over northern Ireland or Scotland, and is slowed by friction with the ground so it gets stronger and veers (becomes more"anticlockwise") at altitude.
Then to add to the fun you get thermal gusts which make the ground-level wind blow briefly in any local direction depending on where the core (the hot spot on the surface) is in relation to the observer.
Plus "roll" winds in the lee of mountains (not a lot in Suffolk, admittedly) where the local surface wind can be blowing in exactly the opposite direction to the upper levels.
And that's just the basics!
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Wind even blows in different directions at the same altitude. One day at work someone standing by the window said "come and look at this, these clouds are going to crash into each other", so I did, and they did: one cloud from the left, another from the right, and the collision looked like a nuclear mushroom cloud. I assume there was something causing a rising thermal, but I've no idea what.
Walking in the Lake district one day there was a westerly hoolie blowing in off the sea all day, but the clouds weren't moving. There was a clear north south dividing line above me, with clear sky to the west and cloud to the right, and it stayed put because it was the mountains I was standing on that were creating the cloud by deflecting the humid air upwards.
I once read a meteorology book book which suggested a simple technique for forecasting weather is to compare the direction of the high altitude clouds with the low altitude ones so that you can see if the weather system is approaching or departing, but the problem is that the low altitude cloud is often obstructing the view of the higher altitude.