The_'Frostnumber'_is_in_part_dependent_on_the_quality_of_the

Mr F.IJnsen in a scientific research document has laid down the fundamental principes, that he used to classify winters since 1200. For that, old chronicles were used. The data for the period 1 November till 31 March was read. Subsequently he classified a winter according the following Standard:

Frost number

84 or higher = extremely cold

68 to 83 = very very cold

44 to 67 = very cold

28 to 43 = cold

IJnsen used the following formula to calculate the 'Frost number' (V):

V = 0,00275v2 + 0,667y + 1,11z

where

v= the number of days with frost

z= equals the number of very cold days (highest temperature -10°C(14°F) or even colder)

Y= equals the number of ice-days (days on which it also freezes during day-time)

The severest winter, as far as the 'Frost number' as calculated above, is concerned, was the winter of 1962/1963. This winter had the highest 'Frost number' during the 150 year period to 1999. With a 'Frost number' of 84, it barely reached the classification 'Extremely cold'.

'Very cold' winters (with a 'Frost number' between 44 and 67) happened over a 100-year period on 15 different times. The Standard for a Ned-H3 'Quality winter A' (V=32) is thus a cold winter, whilst a Ned-H3 'Quality winter B' (V=18) is a 'normal' Dutch winter. As indicated earlier, both winters possess an equability, as for as trialing for the winter-hardiness of fuchsias. That was a result from the additional points to review, namely 'positive influence snow-cover for Quality winter A', and the 'negative influence of severe drying for Quality winter B'

'Gelderse Fuchsia Info-site' - November 2008