Хоть бы завтра было тепло.

In this sentence, хоть бы expresses a wish or hope, often with a slightly emotional tone: if only, I just hope, let’s hope.

So Хоть бы завтра было тепло means something like:

• If only it’s warm tomorrow
• I just hope tomorrow is warm
• Let’s hope it’s warm tomorrow

This хоть бы is a fixed expression. On its own, хоть often means at least or even, but in хоть бы + past tense, it becomes a wish formula.

This is one of the most common things that confuses learners.

After бы, Russian very often uses a past tense form to talk about something unreal, wished for, hypothetical, or desired — including the future.

So even though the meaning is future, Russian says:

• Хоть бы завтра было тепло
  literally something like If only tomorrow it were warm

This is similar to English using forms like:

• I wish it were warmer
• If only it were sunny tomorrow

So было is not really marking past time here. It is part of a wish / irrealis structure.

Because будет is a normal future-tense statement, while было бы / хоть бы было expresses a wish.

Compare:

• Завтра будет тепло. = Tomorrow it will be warm.
  This is a straightforward prediction or statement.

• Хоть бы завтра было тепло. = If only tomorrow were warm / I hope tomorrow will be warm.
  This expresses desire, not certainty.

So:

• будет = factual future
• было ... бы / хоть бы было = wished-for or hypothetical situation

Because this is an impersonal weather expression.

Russian often talks about weather without a subject:

• Холодно. = It’s cold.
• Тепло. = It’s warm.
• Было тепло. = It was warm.

English needs it as a dummy subject, but Russian usually does not.

So in Хоть бы завтра было тепло, there is no hidden pronoun that you need to supply in normal Russian. The sentence is naturally subjectless.

Because тепло here is not describing a noun. It is a predicative word meaning warm in the sense of the weather / conditions are warm.

Compare:

• тёплый день = a warm day
  Here тёплый is an adjective describing day.

• Сегодня тепло. = It’s warm today.
  Here тепло describes the general condition, not a noun.

So in your sentence:

• Хоть бы завтра было тепло = If only it were warm tomorrow

You are talking about the weather in general, so тепло is the natural choice.

Because завтра sets the time frame early: tomorrow.

Russian word order is flexible, and this placement sounds very natural. It helps the listener immediately understand that the wish concerns tomorrow.

Possible variants are:

• Хоть бы завтра было тепло.
• Хоть бы было завтра тепло.
• Завтра хоть бы было тепло.

But the first one is the most natural neutral version.

So the order is mainly about focus and natural flow, not a strict grammar rule.

Yes, бы is a particle, and it is very important in Russian.

It often marks:

• hypothetical situations
• wishes
• conditional meaning
• unreal or non-factual situations

In this sentence, it helps create the feeling of if only / I wish.

With хоть, it forms the wish expression хоть бы.

A useful thing to remember is that бы often appears with a past tense form, but the meaning does not have to be past.

No — that would be misleading.

Even though хоть can mean at least in other contexts, хоть бы here is not functioning that way. It is a set expression of wishing.

So you should understand the whole phrase хоть бы as something like:

• if only
• I hope
• let’s hope

Not as at least in this sentence.

It is completely natural in everyday speech and sounds conversational, but not rude or sloppy.

It is the kind of thing a person might say when talking about plans, weather, a trip, or an event:

• Хоть бы завтра было тепло. А то мы на пикник собираемся.
  I hope it’s warm tomorrow. We’re planning a picnic.

So it is common spoken Russian, and it also works fine in informal writing.

They are similar in meaning, but the tone is different.

• Хоть бы завтра было тепло = If only tomorrow were warm / I really hope tomorrow is warm
  This sounds like a personal wish or hope.

• Пусть завтра будет тепло = Let it be warm tomorrow
  This can sound more like a request, exhortation, or even a kind of dramatic or poetic statement.

For everyday hoping, Хоть бы завтра было тепло is often the more natural choice.

This is a very useful contrast.

• Хоть бы завтра было тепло = If only tomorrow is warm / I hope tomorrow is warm
  A straightforward wish.

• Лишь бы завтра было тепло = As long as tomorrow is warm
  This means that this one condition is what matters most.

So:

• хоть бы = expressing hope
• лишь бы = expressing that one condition is enough

Example difference:

• Хоть бы завтра было тепло.
  I just hope it’s warm tomorrow.

• Лишь бы завтра было тепло, а остальное неважно.
  As long as it’s warm tomorrow, the rest doesn’t matter.

Yes, but that is a different structure.

• Хоть бы завтра было тепло = I hope it’s warm tomorrow
  General weather/atmosphere

• Хоть бы завтра был тёплый день = I hope tomorrow is a warm day
  More noun-based, with day explicitly mentioned

Both are grammatical, but the original sentence is more idiomatic for simply talking about the weather.

A rough literal breakdown is:

• Хоть бы = if only / I wish / let’s hope
• завтра = tomorrow
• было = were / would be in this wish structure
• тепло = warm

So very literally:

• If only tomorrow were warm

But in natural English, depending on context, you would usually say:

• I hope it’s warm tomorrow
• If only it’s warm tomorrow
• Let’s hope tomorrow is warm