An evaluation of the applicability of supercooled liquid water content forecasts to the forecasting of aircraft icing
Brown R.
Forecasts of supercooled liquid water content produced by the new cloud and precipitation scheme in the mesoscale version of the Unified Model have been compared with in-situ observations made with the MRF C-130 aircraft. The purpose was to evaluate their applicability to the production of aircraft icing forecasts. Five flights were analysed from frontal cases and one made in supercooled stratocumulus. In the frontal cases, the forecast supercooled liquid water was confined to temperatures above -5 deg C, whilst it was observed down to lower temperatures. When supercooled liquid water was forecast it was nearly always observed. The extent of supercooled liquid water was underestimated even ignoring the temperature at which it was forecast. In the stratocumulus case, with cloud-top temperature -5 deg C, the model forecast extensive supercooled liquid water because ice is not initiated by the new cloud scheme until the cloud-top temperature is below -10 deg C. Significant icing was observed on this occasion. It was concluded that the supercooled liquid water content forecasts could not be used alone to forecast aircraft icing.
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