The Met Office keep falling into the same trap with the forecasts they prepare the evening before for the next day. This one never needed to happen if Alex Burhill had scanned the latest observations before going on air. Here in Strathpeffer temperatures were already sub-zero at 6 PM, and believe it or not there are many other colder places other than Aviemore, Altnaharra or Loch Glascarnoch in northern Scotland where there isn’t an AWS (here for instance).
Alex could have always done a quick McKenzie in his head. What I mean by that is use the old tried and tested McKenzie night minimum forecasting equation – that is add the maximum and the air mass dew point together and half it, the subtract the following constant (K). Each station has a different K constant, I always use a value of 10 for a perfect radiation night.
So yesterday’s max at Altnaharra was 6.1°C, to add to that the air mass dew point of 2°C gives 8, divide by 2, gives 4, and then subtract 10 which gives -6°C, and which would be fairly close to the actual min of -6.6°C. That’s not just a touch of frost as the the severity of frost scale from the Met Office to help.
It wouldn’t have been so bad if the BBC had forecast this frost across northern Scotland but they were just as bad in their evening TV forecasts as the Met Office were in their video forecast.