Great question. Firstly I would say it is the cumulative effect of the weather in a month you would be assessing as a single CE.
Secondly - I think you might be suggesting a too simplistic answer in terms of how it is assessed. The fact that you have had three days of air temperatures less than zero does not mean you move Completion Date by three days. You have to demonstrate the effect that the three extra cold days had on the project overall (and over and above the first 9 days of cold weather). The two days extra of snow might have had much more impact that the extra three days of cold temperature.
As you will see in other discussions within this group it is relatively easy to confirm that a weather compensation event has occurred, It is much more difficult (and subjective) to prove what the extra over effect of that bad weather has resulted in.