The first thing you have to do is discover the database format. Is it CSV? Then use Text::xSV to help parse it. Is it fixed format? Then use the unpack function to split the data. I have seen meterological information in both formats.

Once you have the format and can convince yourself that you are parsing the data properly, I would use a hash to count tornado days. Something like this:

while (<>) {
   # parse line
   my ($date, $state) = ...
   $tornadoes{$state}{$date}++;
}
foreach my $state (1..50) {
    print "State = $state,   tronadoes = ", scalar keys %{$tornadoes{$
+state}}, "\n";
}
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If your dates span more than a year, you will have to add extra logic to parse and filter dates.