きのうの天気はすずしかったです。
- The weather was cool yesterday.

きのうの天気はすずしかったです。 meaning: Yesterday's weather was cool.

The sentence follows a basic Japanese sentence structure: Subject + は (topic marker) + Description. In this case, the subject is きのうの天気 (yesterday's weather), which is followed by the topic marker は, and then the descriptive word すずしかったです (was cool). ⚫︎ The subject, きのうの天気, is the topic of the sentence. ⚫︎ は indicates the topic. ⚫︎ The description, すずしかったです, is an adjective in the past tense, describing the topic.

は is a particle that marks the topic of the sentence. It indicates what the sentence is about. ⚫︎ It's placed after the subject of the sentence. ⚫︎ It often translates to "as for..." or "speaking of..." but is not always directly translated. ⚫︎ In this sentence, は marks きのうの天気 as the topic.

すずしい (cool) is an い-adjective. Japanese い-adjectives change their form to indicate tense and politeness. ⚫︎ To make an い-adjective past tense and polite, you change the final い to かった and add です. ⚫︎ The base form is すずしい. ⚫︎ Past tense form (plain): すずしかった (was cool). ⚫︎ Past tense form (polite): すずしかったです (was cool). This is the form used in the example sentence.

すずしい is an い-adjective meaning "cool." It describes a temperature that is comfortably low, or the weather conditions. ⚫︎ In this sentence, it describes the weather 天気. ⚫︎ It is important to know the meaning of adjectives to understand the sentence. ⚫︎ すずしい is the dictionary form of the adjective, meaning "cool."

きのう means "yesterday". It specifies when the weather was cool. ⚫︎ It is used to indicate the time of the action or state. ⚫︎ It is usually placed at the beginning of the sentence, but can also come before or after は. ⚫︎ This provides context for the sentence and tells us when the weather was cool.