ame ga hurisou nanode, kyou ha tyuurinzyou ni zitensya wo oite basu de kaerimasu

雨が is natural here because the sentence is talking about the specific event rain falling as the thing that seems likely.

• 雨が降りそう = it looks like it’s going to rain
• が marks 雨 as the subject of 降る

If you said 雨は, it would sound more contrastive or topical, as if you were setting rain up as a topic and possibly comparing it with something else. In this sentence, が is the normal choice.

降りそう means looks like it will rain or seems likely to rain.

It comes from:

• 降る = to fall, to rain
• ます-stem: 降り
• そう = looks like / seems likely to

So:

• 降る → 降りそう
• 雨が降りそう = It looks like it’s going to rain

This そう is used for something that appears likely based on the current situation, like dark clouds or the weather.

No, they are different.

• 降りそう = it looks like it will rain
  • based on appearance or signs
• 降るそう = I hear that it will rain
  • based on hearsay or reported information

So in your sentence, 降りそう suggests the speaker thinks rain seems likely from what they see or feel.

Both ので and から can mean because, but they feel a little different.

• ので sounds a bit softer, more explanatory, and slightly more formal
• から can sound more direct or more like the speaker’s personal reason

So:

• 雨が降りそうなので = because it looks like it’s going to rain
• 雨が降りそうだから would also be possible, but it feels a bit more direct

In polite speech like this sentence, ので fits very naturally.

今日は makes today the topic.

The sentence is basically saying: As for today, because it looks like rain, I’ll leave my bicycle in the bicycle parking area and go home by bus.

Using は here highlights today as the time frame being discussed. It can also imply contrast, such as today is different from usual.

For example, the hidden nuance may be:

• usually I go home by bicycle
• today, I’ll go by bus

Japanese often leaves out subjects when they are obvious from context.

In this sentence, 帰ります tells us someone is going home, and the natural interpretation is that the speaker means I.

So even though 私 is not written, the meaning is still understood:

• (私は) 今日 は ... 帰ります

This is very normal in Japanese and happens constantly.

Here, に marks the place where the bicycle will be placed/left.

• 置く = to put / place / leave
• The location where something ends up is often marked with に

So:

• 駐輪場に自転車を置く = leave/put the bicycle in the bicycle parking area

If you used で, it would focus more on the place where an action happens, but with 置く, に is the standard choice when marking where the object is placed.

置いて is the て-form of 置く.

置く can mean:

• to put
• to place
• to leave something somewhere

In this sentence, 置いて links two actions:

1. 駐輪場に自転車を置いて
2. バスで帰ります

So the meaning is:

• I’ll leave my bicycle in the bicycle parking area and go home by bus

The て-form often works like and, especially when actions happen in sequence.

Yes, in context it naturally means something like leave or park the bicycle.

Japanese often uses a more general verb where English uses a more specific one.

• 自転車を置く literally = put/leave the bicycle
• Natural English = park the bicycle or leave the bicycle there

So although the verb is 置く, the real-life meaning here is very close to park.

を marks 自転車 as the direct object of 置く.

• 自転車を置く = to leave/put the bicycle

So:

• 駐輪場に = where the bike is left
• 自転車を = the thing being left

That is why を is used.

Here, で marks the means/method used to go home.

• バスで帰ります = go home by bus

This is a very common use of で:

• 電車で行きます = go by train
• 車で来ました = came by car
• バスで帰ります = go home by bus

So this で does not mean location; it means by means of.

Japanese non-past forms often cover both present and future.

So 帰ります can mean:

• go home
• will go home

In this sentence, because it refers to what the speaker is going to do today, it is understood as future:

• I’ll go home by bus

This is very normal in Japanese.

It breaks down like this:

• 雨が降りそうなので、
  • because it looks like it’s going to rain
• 今日は
  • as for today
• 駐輪場に自転車を置いて
  • leave my bicycle in the bicycle parking area
• バスで帰ります
  • and go home by bus

So the pattern is:

reason + topic/time + action 1 + action 2

This is a very common Japanese sentence structure.

It very likely does, even if it does not say so directly.

Because the sentence says:

• today I’ll leave the bicycle and go home by bus

the listener may naturally infer:

• on other days, I might normally ride the bicycle home

That nuance comes especially from 今日は, which can sound contrastive:

• today is different from usual

But this is an implication, not something explicitly stated.