とあって
(To atte)
because it's / given that it's (special situation).
Connection rules
- +Plain-form clause / noun + とあって.
- +Causal — the X situation is unusual / notable and explains the main clause.
- +Main clause often describes crowds, atmosphere, or unusual behavior.
Examples
1.
休日とあって、公園は大勢の人で賑わった。

Kyuujitsu to a te, kouen wa oozei no hito de nigiwa ta.
Being a holiday, the park was crowded with many people.
「because it's / given that it's (special situation)」
2.
有名な歌手が来るとあって、会場は満員だった。

Yuumei na kashu ga kuru to a te, kaijou wa man'in da ta.
Because a famous singer was coming, the venue was full.
「because it's / given that it's (special situation)」