The World Changed at 10:30 AM


While I can't say that I'm a fanatical weather watcher, I am interested in the way that the contributing factors change and provide the rudimentary basis for weather forecasting (at least in the short term). Tapping the glass of the old wood and bellows barometer to see which way it's moving is fine for a rough guide, but more sophisticated kit can provide a lot more useful data.

I've rambled in the past about the weather station and corresponding web site I run (http://www.primrose-hill.com), and I'm starting to get quite proficient at rudimentary cause/effect recognition. At first it was exciting just to watch the real-time display, but now I generally drift straight into the trends page and look at the range of charts it provides. The usually smooth gradients of these charts provide a good indication of what to expect in the next 12 - 24 hours.

So it was a bit of a shock to see the results shown below a few days ago. OK, so the pressure had been falling steadily overnight and stormy weather was, therefore, anticipated. And then, at around 10:30, it levelled off:

Pressure chart

And within just a couple of minutes the wind direction had completely changed through something like 150 degrees from South West to almost due North:

Wind direction chart

At the same time, this cold North wind brought the ambient temperature down almost instantly by 3 degrees, and then by a further 2 degrees within half an hour. This is the fastest drop in temperature I've ever recorded:

Temperature chart

Meanwhile, the heavens opened and it began to rain. And, briefly, it rained at a rate of over 26 mm (one inch) per hour:

Rainfall rate chart

We'd had some rain earlier in the day, but within a few minutes we'd had another 1.5 mm, climbing to 2 mm within the hour:

Total rainfall chart

I keep hearing about the gradual changes to our climate brought on by global warming, but this almost instantaneous change in the weather (local cooling?) was quite a surprise. And then, within the hour, it was snowing - though I knew that was going to happen because I'd just watched the weather forecast on the TV (and, yes, I know that's cheating)...

In fact they say this will be the coldest winter here in Britain since 1963/4. I can believe it - we've regularly had days where the temperature falls to minus 15°C (5°F) during the night and never gets above minus 5°C (23°F) during the day. They even said that one night last week it was colder in England than at the North Pole. Snow had been lying here for more than four weeks (waiting, as my Grandma would have said, for more). And while it's cold here, most of the Northern hemisphere seems to be suffering as well. I read that the temperature in Northern China was as low as minus 35°C (-31°F) in December so I suppose we're relatively lucky here. And, of course, everyone marvelled at the frozen lighthouse in Ohio.

So I suppose my New Year's resolutions should include buying a set of winter tyres for my car, stocking up on rock salt and shovels, and getting the central heating system serviced regularly. Meanwhile, if you are still at the "watching dials go round stage", you can just play with the semi-real-time page instead of looking at boring charts. It's updated every ten seconds:

Realtime weather display

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