Hello,

you subtract the surface sea level pressure of the Novembers before the 10 mildest Decembers (January / February months) from the Novembers before the 10 coldest Decembers ( January / February months) since 1987. You get the areas of the greatest differences between the two groups, what you can see below are the charts leading to a cold month, just the opposite leads to a mild month in North Western Europe (defined as 55 – 67.5°N 25°W – 0).

Novembers before a cold / mild December:

Novembers before a cold / mild January:

Novembers before a cold / mild February:

Yours

KHB