Why is it the BBC use 850 hPa instead of 2 M temperatures?
It must be a pretty boring job being a weather presenter down at the BBC TV centre. The same old boring forecast to repeat on the News channel twice an hour all morning long, sometimes it’s 30 seconds, occasionally it can run to 3 minutes. So I can understand at times to give them a bit more excitement they like to over egg a story, and invariably when the weather is turning milder, or warmer they roll out the same old colour filled contours for surface temperature, you know the ones that use yellows and oranges such as this. I’m quite convinced that the NWP chart they use on these occasions is in reality for temperatures at 850 hPa (~5000 feet) but I could be wrong.
Of course there is no legend to tell you what temperature each shade of colour represents, although there’s plenty of room for one in the top right. This style of 850 hPa chart from wxcharts.com (below) is much more useful. It shows what the ICON model expects temperatures at 850 hPa to be across the country at 09 UTC on Thursday. As you can see there are some small sub-zero areas over the Highlands, which might have given Simon King a clue about the distinct possibility of a spell of snow over the high ground before it turns to rain, but of course he couldn’t do that with the severe case of Scotia Myopia he has.
Instead of misleading the public Meteogroup should be displaying the 2 M temperature chart rather than the 850 hPA, and as you can see (below) the reason they don’t is because it’s much less startling and dramatic. The reason why it’s less dramatic is that temperatures have been adjusted for topography and the colour scale that wxcharts.com use is rather poor, but at least it’s accurate, which might not mean a lot to Meteogroup. What they could use as an alternative and what I’ve advocated for years is the use of temperature anomaly charts (the difference between the forecast temperature and the long-term average) for that day.