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A companion paper developed a subrefractive fading model, in terms of a minimum effective value, using surface synoptic meteorological data. The concept is extended here to cover the whole subrefractive event, so that using the effective parameter , analog radio systems can be simply designed. In the case of digital systems, severe subrefraction may cause outages due to thermal noise increase and this effect must be considered in design. For plains paths, where subrefraction risks are greatest, a method of estimating the shape of the versus time curve of individual events by using correlations with surface synoptic meteorlogical data is given. By summation of time below each selected value enables statistics of to be produced. Examples of the method are given, and it is shown how regions of subrefraction may be defined.