Zone

Fahrenheit

Centigrade

1

Below –50

Below –45

2

–50 to –40

–45 to –40

3

–40 to –30

–40 to –34

4

–30 to –20

–34 to –29

5

–20 to –10

–29 to –23

6

–10 to 0

–23 to –17

7

0 to 10

–17 to –12

8

10 to 20

–12 to –7

9

20 to 30

–7 to –1

10

30 to 40

–1 to 5