First, I'm not sure "has" or "is" are modal verbs, are they? I thought modal verbs were, for example, could, should, will, etc. What you're referring to are auxillary verbs which help form specific tenses. To your question, we often use the auxillary verb alone (informally). So we might ask, "Is it?" or "Has it?", but never as you've suggested in reverse, without including the auxillary verb. Secondly, with all due respect, I'm not sure Jenna's answer is entirely correct. I've been speaking English longer than both of you collectively have been alive. And, quite honestly, rarely have I heard anyone ask, "Storm passed?" or (worse), "Sun's shining?" So, no, "educated" English speakers (even informally) don't drop the auxillary verb. Be safe. Use them.

Yes, we certainly omit verbs such as 'be' and 'have', but only in some very informal contexts and with people you know well. For example, if you've just taken an exam, it wouldn't be unusual for your friends and family to ask "Exam OK?" afterwards. It's a kind of 'telegraphese', used in casual conversation between people who know each other well. Or if you want to make sure that your child ( or elderly relative!) has paid a visit to the bathroom before you set out on a long car journey, you'd probably check by saying "Been to the loo?". It's a way of being friendly and informal, and making the enquiry seem casual. Or, for example, let's say there are some spiders in a room. You're scared of spiders, but your friend isn't. She offers to remove them. So you go off somewhere else, and then after a while you poke your head tentatively back into the room. In this case, you might say: "Spiders gone?" and your friend might answer: "Yep. Spiders gone!" This is a case where you're using simplified English, almost like 'baby-talk' or 'pidgin English', in order to be deliberately informal and childish. As you can imagine, it suits the situation.

In speech, almost any declarative statement can be made into a question by changing the tone when speaking. There aren’t any omitted verbs (modal or auxiliary) in your examples. (What has been omitted are the articles, which is irregular, and makes them sound very informal and (too) abbreviated.) The storm passed. (statement) The storm passed? (question) The sun’s shining. (statement) The sun’s shining? (question) And in writing, the question mark takes the place of the tone change.

Thank you Jeanna!

Typically, no, unless in very informal conversation. You can make a statement omitting the modal verb, such as “Ah, sun’s shining!” Or “Storm’s passed.” Keep in mind this is used in speech, not formal writing. If you’d like to delve deeper into questions like these, book a lesson with me and I will be happy to help you reach your English goals!