The SCS local cloud predictor. (a) The thick line represents measurements of a sudden humidity increase; that is, a cloud was moving across the STELLA weather stations. The -axis is in seconds and the 2-minute slot needed to close the observatory roof is indicated. The predictor needs in about that time to predict the increase to the actual future value. For the incidence shown this was already the case when the humidity level was still low (50–60% in this case at seconds) and the roof closed well before the cloud could have been trapped inside the observatory bay. (b) The basis for that prediction is the (local) relation between humidity and barometric pressure. This relation is not strict but the likeliness of low humidity, that is, good weather, is high when the pressure is also high, that is, when the data fall within the lower right of above diagram.
