Condense multiple if statements with or operators?
This sort of thing, with a finite set of coditions, is typically done using an array:

var codeIcons=[
      ["basecloud", "wind"],
      ["basecloud", "rain"],
      ["basecloud", "rain"],
      ["basecloud", "thunder"],
      ["basecloud", "thunder"],
      ....
    ];


Then your method simply becomes:

function returnClass(c) {
    c = parseInt(c);
    return (c &lt; codeIcons.length) ? codeIcons[c] : ["none"];
}


Just adding to a set of advantages this method has:


sure, it is hard-coding logic, but, the presentation is better than multiple if-statements.
it is more managable - you can easily add conditions
you know exactly what conditions lead to certain output (you do not need to scan pages of code to find the right conditions
you cannot have bugs where multiple conditions lead to the same result (these types of bugs tend to creep in after maintaining the code - you have multiple or-conditions where c == xxx.
if, further down the road, you want to migrate the logic for what classes/icons to use, and when, you can easily just change where the array-of-values is configured (i.e. it can become a configuration value, not hard-coded.)