Something like this will work, just add more data as needed:
$station_array =
array(
'station1' => array(
'cat1' => array ('val1','val2','val3'),
'cat2' => array ('val1','val2','val3'),
'cat3' => array ('val1','val2','val3')
),
'station2' => array (
'cat1' => array ('val1','val2','val3'),
'cat2' => array ('val1','val2','val3'),
'cat3' => array ('val1','val2','val3')
),
'station3' => array (
'cat1' => array ('val1','val2','val3'),
'cat2' => array ('val1','val2','val3'),
'cat3' => array ('val1','val2','val3')
)
);