I think you are working way too hard :) Convert your dates to epoch seconds

use Time::Local;
my $time = timelocal(0,0,0,$mday,$month,$year);
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then your date comparisons become a simple numeric comparison

also there is no need to make a system call to ls to get the filenames, a file glob would do

@list = <*_weather.*>;
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update: I was working too hard as well :) Your dates are in a sensible format (yyyy-mm-dd), remove the dashes and you can just compare them numerically, much easier :)

update2: thanks to tilly for pointing out I am still working too hard: yyyy-mm-dd can be compared with cmp no need to remove the dashes at all.

--
my $chainsaw = 'Perl';