# Up above your main loop
my $DBH;
my $STH = setup_database();

while (1) {
    . . . SNIP . . .
}

$DBH->disconnect;

sub setup_database {
    my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile" ,"","");
    my $q = "insert into weather_data values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
    return $dbh->prepare($q);
}

sub process_data {
    if ($debug) {
        say "Processing polled data...."
    }
    my $json_line = shift(@_);
    my $dt = DateTime->now();
    $dt->set_time_zone( 'America/Chicago' );
    if ( not exists($json->{'ra'}) ) {
        $json->{ra} = $json->{rr} = 'null';
    }
    if ( not exists($json->{'bbl'}) ) {
        $json->{bbl} = $json->{irl} = $json->{lux} = 'null';
    }
    $STH->execute(undef,$dt->datetime(), $dt->ymd(), $dt->hms(),
                  $json->{'wd'}, $json->{'wv'}, $json->{'tF'}, $json->{'tC'},
                  $json->{'bp'}, $json->{'rh'}, $json->{'li'}, $json->{'ov'},
                  $json->{'lux'}, $json->{'bbl'},  $json->{'irl'}, $json->{'ra'}, $json->{'rr'}
    );
}