Eloh666, check you sync setting for the weather app.

go to settings>accounts&sync, if you click the weather at the bottom, check mark sync weather, and tell how often, i had this problem ( 2.3.3 ) and this sorted it.

 

i dont know about actual weather codes.....i have just been looking through the sensation manual.

it says for the weather app to automatically update... well here is what it says, you could try turning all you location settings on if they are not already

For HTC Sensation to detect your current location and display your local weather in
the Weather app and widget as well as in Clock and Calendar:

 

As long as weather is set to sync and you at least have use wireless networks for location enabled it should work ok.

I personally dont have use gps for location enabled and the only time I had any problems was when I turned off weather sync. Setting it to update every 3 hours is also fine, and will not drain battery much.

Cheers