[jonah] undefined function

[UnixguyinNYC at aol.com]

Jonah was working very well with the exception of weather. Under the weather 
header was blank instead of the weather for the selected area.  So I updated 
my code & now I get the error below. Is the noradar gif supposed to be 
displayed next to the weather header?

Fatal error: Call to undefined function: strtolower() in 
htdocs/horde/jonah/lib/Weather.php on line 174

Any suggestions would be greatly appreciated.

Thanks,
-Charles