Verification of Supercooled Cloud Water Forecasts with In Situ Aircraft Measurements

Abstract

In situ measurements of temperature (Ta), horizontal wind speed (V), dewpoint (Td), total water content (TWC), and cloud and supercooled cloud water (SCW) events, made during 50 flights from three research field programs, have been compared to forecasts made with the High Resolution Model Application Project version of the Global Environmental Multiscale model. The main purpose of the comparisons was to test the accuracy of the forecasts of cloud and SCW fields. The forecast accuracy for Ta, V, and Td agreed closely with the results from radiosonde?model validation experiments, implying that the aircraft?model validation methodology was equally feasible and, therefore, potentially applicable to SCW forecast verifications (which the radiosondes could not validate). The hit rate (HR), false alarm rate (FAR), and true skill statistic (TSS) for cloud forecasts were found to be 0.52, 0.30, and 0.22, respectively, when the model data were inferred at a horizontal resolution of 1.5 km (averaging scale of the aircraft data). The corresponding values for SCW forecasts were 0.37, 0.22, and 0.15, respectively. The HRs (FARs) for cloud and SCW events are sensitive to horizontal resolution and increase to 0.76 (0.50) and 0.66 (0.53), respectively, when a horizontal resolution of 100 km is used. The model TWC was found to agree poorly with aircraft measurements, with the model generally underestimating TWC. For cases when the forecasts and observations of cloud agreed, the SCW-forecast HR, FAR, and TSS were 0.63, 0.22, and 0.41, respectively, which implies that improvement in the model cloud fields would substantially improve the SCW forecast accuracy. The demonstrated comparison methodology will allow a quantitative comparison between different SCW and cloud algorithms. Such a comparison will provide insight into the strengths and weaknesses of these algorithms and will allow the development of more accurate cloud and SCW forecasts.