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 the west of the USA (defined as 30 – 50°N 125 – 95°W).

Novembers before a cold / mild December:

Novembers before a cold / mild January:

Novembers before a cold / mild February:

…………in Alaska

Novembers before a cold / mild December in Alaska:

Novembers before a cold / mild January:

Novembers before a cold / mild February:

Yours

KHB