The appliance of science

I heard Helen Willetts on the Weather for the week ahead last night saying how the low pressure over the Atlantic was set to cross the IONA and bemoaning the fact that the model just couldn’t be specific about where showers would actually fall, using phrases such as :-

  • Some places will get them some places will miss them
  • It’s very difficult to get the detail
  • Very few places are likely to escape those showers
  • Just meandering around this low pressure
  • I wouldn’t like to guarantee anywhere a dry day on Saturday
  • Might focus the showers into central and eastern areas
  • Perhaps fewer showers in the far west but at this distance it’s hard to get that detail right
  • Not raining all the time but they’ll be clusters of quite intense rain
  • We’ve got all those showers established

I think you get the idea. So why didn’t Helen just display an accumulation chart of where the NWP mesoscale model thinks the precipitation will fall over the day or even the next 3 days, and then let the viewer decide on just how wet it’s going to be in their area?

It’s just an idea. Sometimes there may seem to be no discernable pattern in an animation sequence of 72 hourly NWP frames, so why not let the model just add up the accumulations, and a pattern might emerge that we couldn’t see, because sometimes we just can’t see the woods for the trees. Just because the presenter can’t make heads or tails of it – a ‘messy’ situation as it is so often described – doesn’t mean that the model, or come to it the viewer if he is presented with the proper data, can’t.

Here’s an example of where the ICON model thinks the bulk of the rain will fall over next three days over the IONA. Interestingly, if this forecast is right many inland areas of England and Wales won’t get that much rain, although there are a number of hot, or should that be wet spots, including Eastern Scotland, the west and southwest of Wales and along the south coast of the English Channel. It looks to me that this is a mix of convective and dynamic rainfall which looks to be driven in a large part at is usual at this time of year by the SST around our coasts. It’s also noticeable as in the past couple of weeks the northwest of Scotland seems to escape the heaviest of the rain. I’ll be interested to see just how accurate this forecast is.

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