What are the Spring Frost Indices (SFIs)?

The Spring Frost Indices provide data on the heat relationship in spring, when after a mild winter any influential cooling in early spring can cause serious frost damage owing to a low chill sum value. To measure the potential frost damage on developing plants, the Plant CT System calculates two types of SFI:
Gladstones Spring Frost Index (°C) – lets the summation of Tmin , the minimal air temperature value in April; and Tavg (Tmax), the average value of the maximum air temperature values in April; to give the difference of the previous value and the minimum air temperature measured in the month (Gladstones, 2000).
Wolf-Boyer Spring Frost Index (°C) – lets the summation of Tmin , the minimal air temperature value in April; and Tavg (Tmax), the average value of the maximum air temperature values in April; to give the difference of the previous value and the average minimum air temperature measured in the month (Wolf & Boyer, 2003).

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