Minimal changes might be something like:

...
my ($record, $date, $outfile, %stations, $sstation, $linecnt, $pcntg, 
+@values);

...
$date = $ARGV[1];
%stations = map{ $_ => 1 } @ARGV[ 2 .. $#ARGV];
... 
if( $values[0] eq $date && exists $stations{ $sstation } ) {
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• It re-orders the command line arguments to put the station number(s) at the end of the command line.
• It then builds a hash from the station number(s) entered.
• And checks each value of $sstation against the hash using exists

The command line then becomes:

perl midasproc2.pl midas_wxhrly_199901-199912.txt "1999-12-15 11:00" 1
+9260 19261 19262 [...]
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