Words and expressions in English.

Hello, everyone. My friend and me are trying to translate the text from Urkainian to English. We've got a lot of troubles with it, dictionaries don't help much really.
It would be great if you could help us. Thank you. )

1. A state of nature before a thunderstorm when the air is thick and humid etc. Is there one word to describe it?
in Russian: предгрозье
in Ukrainian: передгріззя

2. Expression to descibe the movement of placing weapon on your sholder holding the belt of it. Don't know how to describe it with words. Here is the picture http://www.vetrabotnik.narod.ru/Modelizm/Texts/Uniform/USA/USA024.jpg
The dictionary gave us "fling over one's shoulder", but google didn't find any examples, so we considered it to be wrong.
In Russian: "перебрасывать оружие через плечо"
In Ukrainian: "перекидати зброю через плече"

3. Is it alright to say "the death is (up)on my consience"?
In Russian: "смерть на моей совести"
In Ukrainian: "смерть на моїй совісті"