2009 4cyl: why thicker oil for colder climate and thinner for warmer ?

I'm getting ready for my first oil change and the manual says to use 5w-20 (oil is thicker when engine is cold) for colder climate and 0w-20 (thinner when engine is cold) for warmer climate. If I had to guess I'd use thinner oil in cold climate and thicker in warm climate. Why do they recommend it other way around ?

PS. Does anyone know where do they sell 0w-20 mobile 1 in 5qt jugs ? I checked 2 walmarts and it wasn't there.

 

While don't have my manual in front of me I believe it's as you suspect. I lived in Canada and the thinner oils are used during winter months and thicker in summer.

 

Manual has a chart where they say if its bellow something like 40F use 5w20, and if above 40F use 0w20. I'm just trying to understand why.

 

Looks like a typo to me.

 

yea its the other way around, also i cant find 0-20 in 5 qt so i got 5-30