def _WX(s, wx):
    """Returns TRUE if s contains string wx"""
    if wx == '':
        return False
    # special case for blowing/drifting snow
    ix = s.find(wx)
    if wx == 'SN' and ix > 1:
        if s[ix-2:ix] in ('BL', 'DR'):
            return False
    return ix >= 0