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Notification center weather information.
How do I change it to celcius on iPad?
Change it to Celsius in the weather app.
Bottom right corner, tap the icon, and C/F appears on the bottom left.
Then reset your device.

It should then change in Notification Centre.
 
Change it to Celsius in the weather app.
Bottom right corner, tap the icon, and C/F appears on the bottom left.
Then reset your device.

It should then change in Notification Centre.

I don't have a weather app on the ipad...
 
Settings/general/international/region format

Choose your region or a region that uses Celsius
 
Go to Settings-->General-->international--> Region Format. if you choose US the unit will be Fahrenheit, so just change to a country using metrics system.
 
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