Whilst I'm on the subject of ice, I will explain some interesting weather graphs from last night as well.
In the above graphs you can see a period between 6pm and midnight where the wind speed and wind direction appear to bounce between 0 and maximum (60m/s for wind speed). This odd looking data is generated by our ultrasonic wind sensor. The wind sensor uses four ultrasonic transceivers to determine the wind speed and direction. When the path between these transceivers is blocked the sensor bounces the output between zero and maximum to indicate the problem.
Blockage between the transceivers is often indicative of ice at the observatory, though in the summer it can also be triggered by large amounts of dust in the air.