dāngshí tiānqì hěn lěng.

In Mandarin, time words often come near the beginning of the sentence, before the main description.

So:

• 当时 = at that time / then
• 天气 = the weather
• 很冷 = was cold

The basic pattern is:

Time + topic/subject + comment

So 当时天气很冷 literally feels like:

At that time, the weather was cold.

This word order is very natural in Chinese.

当时 means at that time, then, or at that moment, depending on context.

It refers to a specific time already understood from the conversation or story.

For example:

• 当时天气很冷。 = The weather was cold at that time.
• 我当时不明白。 = I didn’t understand at that time.

A learner should know that 当时 is not just a general before or in the past. It usually points to a particular past situation.

This is one of the most common questions in Mandarin.

In a sentence like this, 很 does not always mean very in a strong way. Very often, it is just used to link the subject with an adjective naturally.

So:

• 天气很冷 usually just means The weather is cold
• not necessarily The weather is very cold

In Mandarin, adjectives can act like verbs, but when making a simple descriptive statement, Chinese often uses 很 before the adjective.

So 很 here is often more grammatical than emphatic.

If you really want to stress very cold, context and tone matter, or you can use stronger words like:

• 非常冷 = extremely cold
• 特别冷 = especially cold

Yes, but it changes the feeling.

天气冷 is grammatically possible, but in many situations it can sound like a contrast, comparison, or a more marked statement.

For example, it may sound closer to:

• The weather was cold (as opposed to something else)
• The weather was indeed cold

For a neutral statement, learners are usually taught:

• 天气很冷

So if you are just describing the weather in a normal way, 很 is the safest and most natural choice.

Because in Mandarin, adjectives can directly describe the subject without 是.

English says:

• The weather was cold

Chinese says:

• 天气很冷

Here, 冷 works like a stative verb or adjective-predicate, so you do not use 是.

So these are correct:

• 天气很冷。
• 天气不冷。

But this is usually wrong:

• 天气是很冷。

You only use 是 in special emphatic structures, not in a basic sentence like this.

天气 specifically means weather.

• 天气很冷。 = The weather is cold.

天 can mean several things, such as:

• sky
• day
• part of words related to nature or time

In everyday speech, people do sometimes say things like:

• 今天很冷。 = Today is cold.

But if you want to talk directly about the weather, 天气 is clearer and more standard.

In Mandarin, words like 冷 are often called adjectives, but they behave differently from English adjectives.

They can function directly as the predicate of a sentence:

• 天气很冷。
• 我很累。
• 他很高。

So in English grammar terms, it may feel like an adjective, but in Chinese sentence structure it behaves a bit like a verb.

That is why Chinese does not need is/are/was here.

The pinyin is:

dāngshí tiānqì hěn lěng

A few pronunciation notes:

• 当时: first tone + second tone
• 天气: first tone + neutral-ish/fourth-tone feeling depending on speech style, but standard pinyin is tiānqì
• 很: third tone
• 冷: third tone

A natural rhythm is:

dāngshí / tiānqì / hěn lěng

In connected speech, two third tones together can affect how they sound. Since 很 and 冷 are both third tone, 很冷 is often pronounced more like:

• hén lěng

That is normal tone sandhi.

Yes, often you can.

• 当时天气很冷。
• 那时候天气很冷。

Both can mean The weather was cold at that time.

But there is a slight difference:

• 当时 often sounds a bit more tied to a specific moment or situation in a story
• 那时候 often feels a little broader, like back then or at that time

In many everyday contexts, they are interchangeable, but 当时 is especially common when narrating events.

The structure is:

当时 + 天气 + 很 + 冷

You can think of it as:

• 当时 = time expression
• 天气 = subject/topic
• 很冷 = description

So the full pattern is:

Time + subject + adjective predicate

This is a very common Mandarin pattern, and you can make many similar sentences with it:

• 今天我很忙。 = Today I’m busy.
• 昨天他很高兴。 = Yesterday he was happy.
• 那时候房间很安静。 = At that time, the room was quiet.