use strict;
use warnings;

while ( my $line = <DATA> ) {
    $line =~ s{ \s (M?\d{2}) / (M?\d{2}) \s }
              { sprintf ' %d/%d ', convert($1), convert($2) }xeg;
    print $line;
}

sub convert { $_[0] =~ s/M/-/r * 9/5 + 32 };

__DATA__
KSMO 181551Z 00000KT 10SM CLR 14/08 A3009 RMK AO2 SLP189 T01440083
PAFA 190153Z 00000KT 5SM -SN BR FEW012 BKN025 OVC070 M07/M08 A2959 RMK AO2 SLP030 T10671078

##</code><code>##

KSMO 181551Z 00000KT 10SM CLR 57/46 A3009 RMK AO2 SLP189 T01440083
PAFA 190153Z 00000KT 5SM -SN BR FEW012 BKN025 OVC070 19/17 A2959 RMK AO2 SLP030 T10671078