Seriously, he has to output to FORTRAN! ( Fortran::Format ). Think what that's doing to him! Show him some perl love!

I've chosen a data driven design. I've extracted all the field options to one place $fields: defining the regexp to parse the string, possible fixups and the fortran output format.

I've added Getopt::Long to let the user pick a specific range of dates. All of the configurable information is at the start of the script. I'd eventually pull the parsing into a module with a callback to print the output lines, so that the script just contains the part of user interest.

WWW::Mechanize::Cached will build a nice local-side cache, which is handy when you realize half-way through a huge scrape run that you need to grab an extra field. I query if the last request came out of cache, and skip sleeping before the next request.

#!/usr/bin/perl

use strict;
use warnings;

use WWW::Mechanize::Cached;
use Date::Simple::D8 (':all');
use Fortran::Format;
use Getopt::Long;

#configuration:
my $start_date = '19400101';
my $last_date  = '20090718';
my $filename   = "c:/perl/scripts/496/hla.txt";
my $root_url   = "http://bub2.meteo.psu.edu/wxstn/wxstn.htm";
my $help       = 0;

my $result = GetOptions(
    "start=s" => \$start_date,
    "end=s"   => \$last_date,
    "help"    => \$help,
);
my $usage = <<EOS;
$0 - Parse $root_url from $start_date to $last_date
Options:
 --start=19400101
 --end=20090718
EOS
die $usage if ( $help or !$result );

my $fields = {
    depth => {
        regexp => qr/Rain or Liquid Equivalent\s+:\s+(\S*)/,
        format => "I2.1,6X",
        fix    => { TRACE => 99, '(N/A)' => 99, '0' => 99 },
    },
    rain => {
        regexp => qr/Snow and\/or Ice Pellets\s+:\s+(\S*)/,
        format => "F4.2,6X",
        fix    => { TRACE => '0.00' },
    },
    snow => {
        regexp => qr/Snow Depth\s+:\s+(\S*)/,
        format => "F4.2,6X",
        fix    => { TRACE => '0.00' },
    },
    hdd => {
        regexp => qr/Degree-Days\s+:\s+(\S*)/,
        format => "I2.1,6X",
    }
};

sub print_output {
    my ( $date, $data, $fortran ) = @_;

    my @data    = @$data;
    my %fortran = %$fortran;

    my $output =
      join( " ", $date, @data[ 0 .. 2 ], @fortran{qw( depth hdd rain s
+now )} )
      . "\n";

    print $output;
    print OUTPUT $output;
}

#### end configuration

# Open file for writing
open( OUTPUT, '>', $filename ) or die "open: $!\n";

# Initiate browsing agent
my $mech = WWW::Mechanize::Cached->new( keep_alive => 1 );

# Create date list
my $date     = Date::Simple::D8->new($start_date)->prev;
my $end_date = Date::Simple::D8->new($last_date);

$mech->get($root_url);
while ( $date->next <= $end ) {

    # Submit the first form
    my $resp = $mech->submit_form(
        form_number => 1,
        fields      => { dtg => $date }
    );

    # Download the resulting page, text only, and scrape for data
    my $page = $mech->content( format => 'text' );
    my @data = ( $page =~ /:\s\s\s\s(\d\d)/g );
    my %fortran;
    foreach $field ( keys %$fields ) {
        my $regexp = $fields->{$field}->{regexp};
        my $format = $fields->{$field}->{format};
        my $fix    = $fields->{$field}->{fix} || {};

        #parse page for this field
        my ($parsed) = $page =~ /$regexp/;

        #fix field
        foreach my $key ( keys %fix ) {
            $parsed = $fix{$key}
              if $parsed eq $key;
        }

        # Format the output for Fortran analysis
        chomp( my $f = Fortran::Format->new($format)->write($parsed) )
+;
        $fortran{$field} = $f;

    }

    # Prepare output for screen and file
    print_output( $date, \@data, \%fortran );

    sleep .1 unless $mech->is_cached();
    $mech->back();
}    # Exit the loop

# Close the written file
close(FH);
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